mxwrite.cpp

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#include "mxwrite.hpp"
#include <algorithm>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <thread>
#include <utility>
#ifdef MXWRITE_HAS_CUDA_COPY
#include <cuda_runtime.h>
#endif
extern "C" {
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/imgutils.h>
#include <libavutil/mastering_display_metadata.h>
#include <libavutil/mathematics.h>
#include <libavutil/opt.h>
#include <libavutil/pixdesc.h>
#include <libswscale/swscale.h>
}
 
namespace {
 
    // --- HDR helpers -----------------------------------------------------------
    // SMPTE ST.2084 (PQ) constants.
    constexpr float kPqM1 = 2610.0f / 16384.0f;
    constexpr float kPqM2 = (2523.0f / 4096.0f) * 128.0f;
    constexpr float kPqC1 = 3424.0f / 4096.0f;
    constexpr float kPqC2 = (2413.0f / 4096.0f) * 32.0f;
    constexpr float kPqC3 = (2392.0f / 4096.0f) * 32.0f;
    // SDR reference white as a fraction of PQ peak (100 nits / 10000 nits).
    constexpr float kSdrRefFraction = 100.0f / 10000.0f;
 
    inline float srgbEotf(float v) {
        // sRGB non-linear -> linear light.
        return (v <= 0.04045f) ? (v / 12.92f) : std::pow((v + 0.055f) / 1.055f, 2.4f);
    }
 
    inline float pqOetf(float L) {
        // L in [0,1] where 1.0 == 10000 nits; returns PQ code value in [0,1].
        const float Lm = std::pow(std::max(0.0f, L), kPqM1);
        const float num = kPqC1 + kPqC2 * Lm;
        const float den = 1.0f + kPqC3 * Lm;
        return std::pow(num / den, kPqM2);
    }
 
    inline uint16_t clamp10(float v) {
        if (v < 0.0f)
            v = 0.0f;
        if (v > 1023.0f)
            v = 1023.0f;
        return static_cast<uint16_t>(v + 0.5f);
    }
 
    // Convert one RGBA8 row pair + 2 UV rows into BT.2020 PQ YUV420P10LE.
    // Assumes RGBA input is sRGB-gamma-encoded BT.709 SDR (which is what the
    // shader pipeline produces for HDR inputs after the 8-bit swscale path).
    // Output is limited-range 10-bit. Y: [64..940], UV: [64..960] centered at 512.
    void convertRgbaToBt2020PqYuv420p10(const uint8_t *rgba, int src_stride_bytes, uint16_t *y_plane, int y_stride_shorts, uint16_t *u_plane, int u_stride_shorts, uint16_t *v_plane, int v_stride_shorts, int width, int height) {
        // BT.2020 non-constant luminance RGB->YUV (limited range).
        // E'Y = 0.2627*R + 0.6780*G + 0.0593*B
        // E'Pb = (B - Y) / 1.8814
        // E'Pr = (R - Y) / 1.4746
        // Limited 10-bit: Y: 0..1 -> 64..940 (range 876), UV: -0.5..0.5 -> 64..960 (range 896, center 512).
        constexpr float kKr = 0.2627f;
        constexpr float kKg = 0.6780f;
        constexpr float kKb = 0.0593f;
        constexpr float kPbDiv = 1.0f / 1.8814f;
        constexpr float kPrDiv = 1.0f / 1.4746f;
 
        for (int y = 0; y < height; y += 2) {
            const int y1 = std::min(y + 1, height - 1);
            const uint8_t *row0 = rgba + y * src_stride_bytes;
            const uint8_t *row1 = rgba + y1 * src_stride_bytes;
            uint16_t *yr0 = y_plane + y * y_stride_shorts;
            uint16_t *yr1 = y_plane + y1 * y_stride_shorts;
            uint16_t *ur = u_plane + (y / 2) * u_stride_shorts;
            uint16_t *vr = v_plane + (y / 2) * v_stride_shorts;
 
            for (int x = 0; x < width; x += 2) {
                const int x1 = std::min(x + 1, width - 1);
 
                // Load 2x2 block of sRGB 8-bit pixels.
                auto loadPq = [](const uint8_t *px, float &Y, float &U, float &V) {
                    // sRGB 8-bit -> linear [0,1]
                    const float r = srgbEotf(px[0] * (1.0f / 255.0f));
                    const float g = srgbEotf(px[1] * (1.0f / 255.0f));
                    const float b = srgbEotf(px[2] * (1.0f / 255.0f));
                    // Scale SDR linear [0,1] (reference 100 nits) to PQ fractional.
                    const float rL = r * kSdrRefFraction;
                    const float gL = g * kSdrRefFraction;
                    const float bL = b * kSdrRefFraction;
                    // PQ encode per channel (RGB PQ).
                    const float rp = pqOetf(rL);
                    const float gp = pqOetf(gL);
                    const float bp = pqOetf(bL);
                    // BT.2020 RGB' -> YUV'.
                    Y = kKr * rp + kKg * gp + kKb * bp;
                    U = (bp - Y) * kPbDiv;
                    V = (rp - Y) * kPrDiv;
                };
 
                float Y00, U00, V00;
                float Y01, U01, V01;
                float Y10, U10, V10;
                float Y11, U11, V11;
                loadPq(row0 + x * 4, Y00, U00, V00);
                loadPq(row0 + x1 * 4, Y01, U01, V01);
                loadPq(row1 + x * 4, Y10, U10, V10);
                loadPq(row1 + x1 * 4, Y11, U11, V11);
 
                // Y: per-pixel, limited-range 10-bit.
                yr0[x] = clamp10(Y00 * 876.0f + 64.0f);
                yr0[x1] = clamp10(Y01 * 876.0f + 64.0f);
                yr1[x] = clamp10(Y10 * 876.0f + 64.0f);
                yr1[x1] = clamp10(Y11 * 876.0f + 64.0f);
 
                // UV: 4:2:0 average of 2x2 block.
                const float Uavg = 0.25f * (U00 + U01 + U10 + U11);
                const float Vavg = 0.25f * (V00 + V01 + V10 + V11);
                ur[x / 2] = clamp10(Uavg * 896.0f + 512.0f);
                vr[x / 2] = clamp10(Vavg * 896.0f + 512.0f);
            }
        }
    }
 
    // Convert 16-bit RGBA (already BT.2020-primaries, PQ- or HLG-encoded) into
    // BT.2020 YUV420P10LE limited-range. No transfer conversion is applied here
    // because the GPU HDR encode pass already produced the non-linear signal.
    // @c rgba is tightly-packed 16-bit (8 bytes/pixel), @c src_stride_shorts is
    // the row stride in 16-bit samples (i.e. bytes/2).
    void convertBt2020Rgba16EncodedToYuv420p10(const uint16_t *rgba, int src_stride_shorts, uint16_t *y_plane, int y_stride_shorts, uint16_t *u_plane, int u_stride_shorts, uint16_t *v_plane, int v_stride_shorts, int width, int height) {
        constexpr float kKr = 0.2627f;
        constexpr float kKg = 0.6780f;
        constexpr float kKb = 0.0593f;
        constexpr float kPbDiv = 1.0f / 1.8814f;
        constexpr float kPrDiv = 1.0f / 1.4746f;
        constexpr float kInv65535 = 1.0f / 65535.0f;
 
        for (int y = 0; y < height; y += 2) {
            const int y1 = std::min(y + 1, height - 1);
            const uint16_t *row0 = rgba + y * src_stride_shorts;
            const uint16_t *row1 = rgba + y1 * src_stride_shorts;
            uint16_t *yr0 = y_plane + y * y_stride_shorts;
            uint16_t *yr1 = y_plane + y1 * y_stride_shorts;
            uint16_t *ur = u_plane + (y / 2) * u_stride_shorts;
            uint16_t *vr = v_plane + (y / 2) * v_stride_shorts;
 
            for (int x = 0; x < width; x += 2) {
                const int x1 = std::min(x + 1, width - 1);
 
                auto load = [&](const uint16_t *px, float &Y, float &U, float &V) {
                    const float rp = px[0] * kInv65535;
                    const float gp = px[1] * kInv65535;
                    const float bp = px[2] * kInv65535;
                    Y = kKr * rp + kKg * gp + kKb * bp;
                    U = (bp - Y) * kPbDiv;
                    V = (rp - Y) * kPrDiv;
                };
 
                float Y00, U00, V00;
                float Y01, U01, V01;
                float Y10, U10, V10;
                float Y11, U11, V11;
                load(row0 + x * 4, Y00, U00, V00);
                load(row0 + x1 * 4, Y01, U01, V01);
                load(row1 + x * 4, Y10, U10, V10);
                load(row1 + x1 * 4, Y11, U11, V11);
 
                yr0[x] = clamp10(Y00 * 876.0f + 64.0f);
                yr0[x1] = clamp10(Y01 * 876.0f + 64.0f);
                yr1[x] = clamp10(Y10 * 876.0f + 64.0f);
                yr1[x1] = clamp10(Y11 * 876.0f + 64.0f);
 
                const float Uavg = 0.25f * (U00 + U01 + U10 + U11);
                const float Vavg = 0.25f * (V00 + V01 + V10 + V11);
                ur[x / 2] = clamp10(Uavg * 896.0f + 512.0f);
                vr[x / 2] = clamp10(Vavg * 896.0f + 512.0f);
            }
        }
    }
 
} // namespace
 
std::mutex transfer_audio_mutex;
 
bool is_format_supported(const char *filename) {
    const char *ext = strrchr(filename, '.');
    if (!ext)
        return false;
    // Lowercase the extension for case-insensitive comparison.
    std::string lower_ext(ext);
    std::transform(lower_ext.begin(), lower_ext.end(), lower_ext.begin(), [](unsigned char c) { return std::tolower(c); });
    static const char *kSupported[] = {".mp4", ".mkv", ".mov", ".avi", ".m4v", ".ts", ".mts", ".m2ts", ".mpg", ".mpeg", ".flv", ".f4v", ".3gp", ".3g2", ".wmv", ".asf", ".vob"};
    for (const char *s : kSupported) {
        if (lower_ext == s)
            return true;
    }
    return false;
}
 
void cleanup_contexts(AVFormatContext *source_ctx, AVFormatContext *dest_ctx, AVFormatContext *output_ctx) {
    if (source_ctx)
        avformat_close_input(&source_ctx);
    if (dest_ctx)
        avformat_close_input(&dest_ctx);
    if (output_ctx) {
        if (!(output_ctx->oformat->flags & AVFMT_NOFILE))
            avio_closep(&output_ctx->pb);
        avformat_free_context(output_ctx);
    }
}
 
void transfer_audio(std::string_view sourceAudioFile, std::string_view destVideoFile) {
    std::lock_guard<std::mutex> lock(transfer_audio_mutex);
    if (!is_format_supported(destVideoFile.data())) {
        std::cerr << "Unsupported output format. Supported formats: .mp4, .mkv, .avi, .mov\n";
        return;
    }
 
    AVFormatContext *source_ctx = nullptr, *dest_ctx = nullptr, *output_ctx = nullptr;
    int source_audio_idx = -1, dest_video_idx = -1, dest_audio_idx = -1;
    std::string temp_output = std::string(destVideoFile) + ".tmp";
 
    if (avformat_open_input(&source_ctx, sourceAudioFile.data(), nullptr, nullptr) != 0 || avformat_open_input(&dest_ctx, destVideoFile.data(), nullptr, nullptr) != 0) {
        std::cerr << "Failed to open input files\n";
        cleanup_contexts(source_ctx, dest_ctx, output_ctx);
        return;
    }
 
    if (avformat_find_stream_info(source_ctx, nullptr) < 0 || avformat_find_stream_info(dest_ctx, nullptr) < 0) {
        std::cerr << "Failed to find stream info\n";
        cleanup_contexts(source_ctx, dest_ctx, output_ctx);
        return;
    }
 
    for (unsigned i = 0; i < source_ctx->nb_streams; ++i) {
        if (source_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
            source_audio_idx = i;
            break;
        }
    }
 
    for (unsigned i = 0; i < dest_ctx->nb_streams; ++i) {
        AVMediaType type = dest_ctx->streams[i]->codecpar->codec_type;
        if (type == AVMEDIA_TYPE_VIDEO)
            dest_video_idx = i;
        else if (type == AVMEDIA_TYPE_AUDIO)
            dest_audio_idx = i;
    }
 
    if (source_audio_idx == -1 || dest_video_idx == -1) {
        std::cerr << "Required streams not found\n";
        cleanup_contexts(source_ctx, dest_ctx, output_ctx);
        return;
    }
 
    const AVOutputFormat *output_fmt = av_guess_format(nullptr, destVideoFile.data(), nullptr);
    if (!output_fmt) {
        output_fmt = av_guess_format("mp4", nullptr, nullptr);
        if (!output_fmt) {
            std::cerr << "Failed to determine output format\n";
            cleanup_contexts(source_ctx, dest_ctx, output_ctx);
            return;
        }
    }
 
    if (avformat_alloc_output_context2(&output_ctx, output_fmt, nullptr, temp_output.c_str()) < 0) {
        std::cerr << "Failed to create output context\n";
        cleanup_contexts(source_ctx, dest_ctx, output_ctx);
        return;
    }
 
    const AVCodec *audio_codec = avcodec_find_decoder(source_ctx->streams[source_audio_idx]->codecpar->codec_id);
    if (!audio_codec) {
        std::cerr << "Failed to find audio decoder\n";
        cleanup_contexts(source_ctx, dest_ctx, output_ctx);
        return;
    }
 
    for (unsigned i = 0; i < dest_ctx->nb_streams; ++i) {
        if (dest_ctx->streams[i]->codecpar->codec_type != AVMEDIA_TYPE_VIDEO) {
            continue;
        }
 
        AVStream *dest_stream = dest_ctx->streams[i];
        AVStream *out_stream = avformat_new_stream(output_ctx, nullptr);
        if (!out_stream) {
            std::cerr << "Failed to create output stream\n";
            cleanup_contexts(source_ctx, dest_ctx, output_ctx);
            return;
        }
 
        if (avcodec_parameters_copy(out_stream->codecpar, dest_stream->codecpar) < 0) {
            std::cerr << "Failed to copy video parameters\n";
            cleanup_contexts(source_ctx, dest_ctx, output_ctx);
            return;
        }
 
        out_stream->time_base = dest_stream->time_base;
        out_stream->codecpar->codec_tag = 0;
    }
 
    AVStream *out_stream = avformat_new_stream(output_ctx, audio_codec);
    if (!out_stream) {
        std::cerr << "Failed to create audio stream\n";
        cleanup_contexts(source_ctx, dest_ctx, output_ctx);
        return;
    }
 
    AVCodecParameters *source_params = source_ctx->streams[source_audio_idx]->codecpar;
    if (avcodec_parameters_copy(out_stream->codecpar, source_params) < 0) {
        std::cerr << "Failed to copy audio parameters\n";
        cleanup_contexts(source_ctx, dest_ctx, output_ctx);
        return;
    }
 
    if (source_params->frame_size == 0) {
        out_stream->codecpar->frame_size = 1024;
    } else {
        out_stream->codecpar->frame_size = source_params->frame_size;
    }
 
    out_stream->time_base = source_ctx->streams[source_audio_idx]->time_base;
    out_stream->codecpar->codec_tag = 0;
    dest_audio_idx = out_stream->index;
 
    if (!(output_ctx->oformat->flags & AVFMT_NOFILE)) {
        if (avio_open(&output_ctx->pb, temp_output.c_str(), AVIO_FLAG_WRITE) < 0) {
            std::cerr << "Failed to open output file\n";
            cleanup_contexts(source_ctx, dest_ctx, output_ctx);
            return;
        }
    }
    if (avformat_write_header(output_ctx, nullptr) < 0) {
        std::cerr << "Failed to write header\n";
        cleanup_contexts(source_ctx, dest_ctx, output_ctx);
        return;
    }
    AVPacket packet;
    while (av_read_frame(dest_ctx, &packet) >= 0) {
        if (packet.stream_index == dest_audio_idx) {
            av_packet_unref(&packet);
            continue;
        }
 
        AVStream *in_stream = dest_ctx->streams[packet.stream_index];
        AVStream *out_stream = output_ctx->streams[packet.stream_index];
        av_packet_rescale_ts(&packet, in_stream->time_base, out_stream->time_base);
 
        if (av_interleaved_write_frame(output_ctx, &packet) < 0) {
            std::cerr << "Failed to write packet\n";
            av_packet_unref(&packet);
            cleanup_contexts(source_ctx, dest_ctx, output_ctx);
            return;
        }
        av_packet_unref(&packet);
    }
 
    int64_t video_duration_ts = 0;
    {
        AVStream *vid_stream = dest_ctx->streams[0];
        if (vid_stream->duration > 0) {
            video_duration_ts = av_rescale_q(vid_stream->duration, vid_stream->time_base, source_ctx->streams[source_audio_idx]->time_base);
        } else if (dest_ctx->duration > 0) {
            AVRational av_tb = {1, AV_TIME_BASE};
            video_duration_ts = av_rescale_q(dest_ctx->duration, av_tb, source_ctx->streams[source_audio_idx]->time_base);
        }
    }
 
    av_seek_frame(source_ctx, source_audio_idx, 0, AVSEEK_FLAG_BACKWARD);
    while (av_read_frame(source_ctx, &packet) >= 0) {
        if (packet.stream_index == source_audio_idx) {
            if (video_duration_ts > 0 && packet.pts != AV_NOPTS_VALUE && packet.pts > video_duration_ts) {
                av_packet_unref(&packet);
                break;
            }
            AVStream *in_stream = source_ctx->streams[packet.stream_index];
            AVStream *out_stream = output_ctx->streams[dest_audio_idx];
            av_packet_rescale_ts(&packet, in_stream->time_base, out_stream->time_base);
            packet.stream_index = dest_audio_idx;
 
            if (av_interleaved_write_frame(output_ctx, &packet) < 0) {
                std::cerr << "Failed to write audio packet\n";
                av_packet_unref(&packet);
                cleanup_contexts(source_ctx, dest_ctx, output_ctx);
                return;
            }
        }
        av_packet_unref(&packet);
    }
    av_write_trailer(output_ctx);
    cleanup_contexts(source_ctx, dest_ctx, output_ctx);
    std::remove(destVideoFile.data());
    std::rename(temp_output.c_str(), destVideoFile.data());
}
 
void Writer::calculateFPSFraction(float fps, int &fps_num, int &fps_den) {
    const float epsilon = 0.001f;
    if (std::fabs(fps - 23.976f) < epsilon) {
        fps_num = 24000;
        fps_den = 1001;
    } else if (std::fabs(fps - 29.97f) < epsilon) {
        fps_num = 30000;
        fps_den = 1001;
    } else if (std::fabs(fps - 47.952f) < epsilon) {
        fps_num = 48000;
        fps_den = 1001;
    } else if (std::fabs(fps - 59.94f) < epsilon) {
        fps_num = 60000;
        fps_den = 1001;
    } else if (std::fabs(fps - 119.88f) < epsilon) {
        fps_num = 120000;
        fps_den = 1001;
    } else {
        float precision = 1000.0f;
        fps_num = static_cast<int>(std::round(fps * precision));
        fps_den = static_cast<int>(precision);
        int gcd = std::gcd(fps_num, fps_den);
        fps_num /= gcd;
        fps_den /= gcd;
    }
}
 
namespace {
 
    // Map an x264-style preset name to an NVENC preset (p1..p7).
    // p1 = fastest/lowest quality, p7 = slowest/highest quality.
    const char *x264_preset_to_nvenc(const std::string &p) {
        if (p == "ultrafast")
            return "p1";
        if (p == "superfast")
            return "p2";
        if (p == "veryfast" || p == "faster")
            return "p3";
        if (p == "fast")
            return "p4";
        if (p == "medium" || p.empty())
            return "p5";
        if (p == "slow" || p == "slower")
            return "p6";
        if (p == "veryslow")
            return "p7";
        // Allow passing NVENC preset names through directly.
        return p.c_str();
    }
 
    bool is_valid_x264_preset(const std::string &p) {
        static const char *presets[] = {"ultrafast", "superfast", "veryfast", "faster", "fast", "medium", "slow", "slower", "veryslow", "placebo"};
        for (const char *n : presets)
            if (p == n)
                return true;
        return false;
    }
 
    std::string lowercase_ascii(std::string text) {
        std::transform(text.begin(), text.end(), text.begin(), [](unsigned char ch) { return static_cast<char>(std::tolower(ch)); });
        return text;
    }
 
    struct FfmpegOption {
        std::string name;
        std::string value;
    };
 
    int option_base_type(AVOptionType type) {
#if LIBAVUTIL_VERSION_MAJOR >= 60
        return static_cast<int>(type) & ~AV_OPT_TYPE_FLAG_ARRAY;
#else
        return static_cast<int>(type);
#endif
    }
 
    bool looks_like_option(const std::string &token) {
        if (token.size() < 2 || token.front() != '-') {
            return false;
        }
        const unsigned char next = static_cast<unsigned char>(token[1]);
        return !std::isdigit(next) && token[1] != '.';
    }
 
    bool tokenize_ffmpeg_options(const std::string &text, std::vector<std::string> &tokens, std::string &error) {
        std::string token;
        bool token_started = false;
        bool escaped = false;
        char quote = '\0';
 
        for (char ch : text) {
            if (escaped) {
                token.push_back(ch);
                token_started = true;
                escaped = false;
                continue;
            }
            if (ch == '\\' && quote != '\'') {
                escaped = true;
                token_started = true;
                continue;
            }
            if (quote != '\0') {
                if (ch == quote) {
                    quote = '\0';
                } else {
                    token.push_back(ch);
                }
                token_started = true;
                continue;
            }
            if (ch == '\'' || ch == '"') {
                quote = ch;
                token_started = true;
            } else if (std::isspace(static_cast<unsigned char>(ch))) {
                if (token_started) {
                    tokens.push_back(token);
                    token.clear();
                    token_started = false;
                }
            } else {
                token.push_back(ch);
                token_started = true;
            }
        }
 
        if (escaped) {
            error = "trailing escape character";
            return false;
        }
        if (quote != '\0') {
            error = "unterminated quote";
            return false;
        }
        if (token_started) {
            tokens.push_back(token);
        }
        return true;
    }
 
    std::string normalize_ffmpeg_option_name(std::string name) {
        while (!name.empty() && name.front() == '-') {
            name.erase(name.begin());
        }
 
        const size_t stream_specifier = name.find(':');
        if (stream_specifier != std::string::npos) {
            const std::string suffix = name.substr(stream_specifier + 1);
            if (suffix == "v" || suffix.starts_with("v:")) {
                name.erase(stream_specifier);
            }
        }
        return name;
    }
 
    bool is_codec_name(const std::string &value) {
        const std::string codec = lowercase_ascii(value);
        return codec == "h265_nvenc" || codec == "h264" || codec == "h265" || codec == "hevc" || codec == "nvenc" || codec == "software" || codec == "auto" || avcodec_find_encoder_by_name(codec.c_str()) != nullptr;
    }
 
    bool parse_ffmpeg_options(const std::string &text, std::vector<FfmpegOption> &options) {
        std::vector<std::string> tokens;
        std::string error;
        if (!tokenize_ffmpeg_options(text, tokens, error)) {
            std::cerr << "MXWrite: invalid extra FFmpeg parameters: " << error << ".\n";
            return false;
        }
 
        for (size_t index = 0; index < tokens.size(); ++index) {
            std::string token = tokens[index];
            if (!looks_like_option(token)) {
                if (index == 0 && is_codec_name(token)) {
                    options.push_back({"codec", token});
                } else {
                    std::cerr << "MXWrite: ignoring non-option extra parameter '" << token << "' (filenames are selected by Writer::open).\n";
                }
                continue;
            }
 
            while (!token.empty() && token.front() == '-') {
                token.erase(token.begin());
            }
            const size_t equals = token.find('=');
            std::string name = normalize_ffmpeg_option_name(token.substr(0, equals));
            std::string value;
            if (equals != std::string::npos) {
                value = token.substr(equals + 1);
            } else if (index + 1 < tokens.size() && !looks_like_option(tokens[index + 1])) {
                value = tokens[++index];
            } else {
                value = "1";
            }
 
            if (name.empty()) {
                std::cerr << "MXWrite: invalid empty FFmpeg option name.\n";
                return false;
            }
            options.push_back({std::move(name), std::move(value)});
        }
        return true;
    }
 
    const std::string *find_ffmpeg_option(const std::vector<FfmpegOption> &options, const std::string &name) {
        for (auto option = options.rbegin(); option != options.rend(); ++option) {
            if (option->name == name) {
                return &option->value;
            }
        }
        return nullptr;
    }
 
    bool is_reserved_ffmpeg_option(const std::string &name) { return name == "c" || name == "codec" || name == "vcodec" || name == "pix_fmt" || name == "pixel_format"; }
 
    bool apply_ffmpeg_options(const std::vector<FfmpegOption> &options, AVCodecContext *context, AVFormatContext *output_context) {
        for (const FfmpegOption &option : options) {
            if (is_reserved_ffmpeg_option(option.name)) {
                continue;
            }
 
            int result = AVERROR_OPTION_NOT_FOUND;
            if (context->priv_data) {
                result = av_opt_set(context->priv_data, option.name.c_str(), option.value.c_str(), 0);
            }
            if (result == AVERROR_OPTION_NOT_FOUND) {
                result = av_opt_set(context, option.name.c_str(), option.value.c_str(), 0);
            }
            if (result == AVERROR_OPTION_NOT_FOUND && output_context->priv_data) {
                result = av_opt_set(output_context->priv_data, option.name.c_str(), option.value.c_str(), 0);
            }
            if (result < 0) {
                char error_text[AV_ERROR_MAX_STRING_SIZE] = {};
                av_strerror(result, error_text, sizeof(error_text));
                std::cerr << "MXWrite: FFmpeg option '-" << option.name << " " << option.value << "' was rejected: " << error_text << ".\n";
                return false;
            }
        }
        return true;
    }
 
    bool set_named_encoder_option(void *object, const char *name, const std::string &value) {
        if (!object || value.empty()) {
            return false;
        }
        const AVOption *option = av_opt_find(object, name, nullptr, 0, 0);
        if (!option) {
            return false;
        }
        const int base_type = option_base_type(option->type);
        const bool textual = base_type == AV_OPT_TYPE_STRING || base_type == AV_OPT_TYPE_DICT || base_type == AV_OPT_TYPE_BINARY;
        const bool numeric_text = std::isdigit(static_cast<unsigned char>(value.front())) || value.front() == '-' || value.front() == '+' || value.front() == '.';
        if (!textual && !numeric_text) {
            const AVOption *named_value = av_opt_find(object, value.c_str(), option->unit, 0, 0);
            if (!named_value || named_value->type != AV_OPT_TYPE_CONST) {
                return false;
            }
        }
        return av_opt_set(object, name, value.c_str(), 0) >= 0;
    }
 
    bool is_nvenc_tune(const std::string &tune) { return tune == "hq" || tune == "uhq" || tune == "ll" || tune == "ull" || tune == "lossless"; }
 
    std::string nvenc_preset_to_software(const std::string &preset) {
        if (preset == "p1")
            return "ultrafast";
        if (preset == "p2")
            return "superfast";
        if (preset == "p3")
            return "veryfast";
        if (preset == "p4")
            return "fast";
        if (preset == "p5")
            return "medium";
        if (preset == "p6")
            return "slow";
        if (preset == "p7")
            return "veryslow";
        return preset;
    }
 
    std::vector<FfmpegOption> software_fallback_options(const std::vector<FfmpegOption> &options, bool use_hevc_codec) {
        std::vector<FfmpegOption> translated;
        bool enable_lossless = false;
 
        for (const FfmpegOption &option : options) {
            FfmpegOption value = option;
            if (value.name == "preset") {
                value.value = nvenc_preset_to_software(lowercase_ascii(value.value));
            } else if (value.name == "tune") {
                const std::string tune = lowercase_ascii(value.value);
                if (tune == "lossless") {
                    enable_lossless = true;
                    continue;
                }
                if (tune == "hq" || tune == "uhq") {
                    continue;
                }
                if (tune == "ll" || tune == "ull") {
                    value.value = "zerolatency";
                }
            } else if (value.name == "profile" && lowercase_ascii(value.value) == "rext") {
                value.value = use_hevc_codec ? "main444-8" : "high444";
            } else if (value.name == "rgb_mode" || value.name == "rc") {
                continue;
            } else if (value.name == "cq") {
                value.name = "crf";
            }
            translated.push_back(std::move(value));
        }
 
        if (enable_lossless) {
            if (use_hevc_codec) {
                bool appended = false;
                for (FfmpegOption &option : translated) {
                    if (option.name == "x265-params") {
                        if (!option.value.empty())
                            option.value += ':';
                        option.value += "lossless=1";
                        appended = true;
                    }
                }
                if (!appended) {
                    translated.push_back({"x265-params", "lossless=1"});
                }
            } else {
                translated.push_back({"qp", "0"});
            }
        }
        return translated;
    }
 
    std::vector<AVPixelFormat> supported_pixel_formats(const AVCodec *codec) {
        std::vector<AVPixelFormat> formats;
        if (!codec) {
            return formats;
        }
 
#if LIBAVCODEC_VERSION_MAJOR >= 61
        const void *configurations = nullptr;
        int configuration_count = 0;
        if (avcodec_get_supported_config(nullptr, codec, AV_CODEC_CONFIG_PIX_FORMAT, 0, &configurations, &configuration_count) >= 0 && configurations) {
            const auto *pixel_formats = static_cast<const AVPixelFormat *>(configurations);
            formats.assign(pixel_formats, pixel_formats + configuration_count);
        }
#else
        if (codec->pix_fmts) {
            for (const AVPixelFormat *format = codec->pix_fmts; *format != AV_PIX_FMT_NONE; ++format) {
                formats.push_back(*format);
            }
        }
#endif
        return formats;
    }
 
    bool is_hardware_pixel_format(AVPixelFormat format) {
        const AVPixFmtDescriptor *descriptor = av_pix_fmt_desc_get(format);
        return descriptor && (descriptor->flags & AV_PIX_FMT_FLAG_HWACCEL) != 0;
    }
 
    AVPixelFormat choose_software_pixel_format(const AVCodec *codec, AVPixelFormat requested_format) {
        const std::vector<AVPixelFormat> formats = supported_pixel_formats(codec);
        auto is_usable = [](AVPixelFormat format) { return !is_hardware_pixel_format(format) && sws_isSupportedOutput(format); };
 
        if (requested_format != AV_PIX_FMT_NONE) {
            if (!is_usable(requested_format)) {
                return AV_PIX_FMT_NONE;
            }
            if (formats.empty() || std::find(formats.begin(), formats.end(), requested_format) != formats.end()) {
                return requested_format;
            }
            return AV_PIX_FMT_NONE;
        }
 
        static constexpr AVPixelFormat preferred_formats[] = {AV_PIX_FMT_YUV420P, AV_PIX_FMT_NV12, AV_PIX_FMT_YUV422P, AV_PIX_FMT_YUV444P, AV_PIX_FMT_YUV420P10LE, AV_PIX_FMT_YUV422P10LE, AV_PIX_FMT_YUV444P10LE, AV_PIX_FMT_BGRA, AV_PIX_FMT_RGBA};
        if (formats.empty()) {
            return AV_PIX_FMT_YUV420P;
        }
        for (AVPixelFormat preferred : preferred_formats) {
            if (std::find(formats.begin(), formats.end(), preferred) != formats.end() && is_usable(preferred)) {
                return preferred;
            }
        }
        for (AVPixelFormat format : formats) {
            if (is_usable(format)) {
                return format;
            }
        }
        return AV_PIX_FMT_NONE;
    }
 
    bool codec_uses_hardware(const AVCodec *codec) {
        if (!codec) {
            return false;
        }
        if ((codec->capabilities & (AV_CODEC_CAP_HARDWARE | AV_CODEC_CAP_HYBRID)) != 0) {
            return true;
        }
        for (int index = 0; avcodec_get_hw_config(codec, index); ++index) {
            return true;
        }
        const std::string name = codec->name ? lowercase_ascii(codec->name) : std::string{};
        static constexpr std::string_view hardware_markers[] = {"_nvenc", "_qsv", "_vaapi", "_amf", "_v4l2m2m", "_videotoolbox", "_mediafoundation", "_vulkan"};
        return std::any_of(std::begin(hardware_markers), std::end(hardware_markers), [&name](std::string_view marker) { return name.find(marker) != std::string::npos; });
    }
 
    std::string option_type_name(AVOptionType type) {
        const int base_type = option_base_type(type);
        switch (base_type) {
        case AV_OPT_TYPE_FLAGS:
            return "flags";
        case AV_OPT_TYPE_INT:
            return "integer";
        case AV_OPT_TYPE_INT64:
            return "integer64";
        case AV_OPT_TYPE_DOUBLE:
            return "double";
        case AV_OPT_TYPE_FLOAT:
            return "float";
        case AV_OPT_TYPE_STRING:
            return "string";
        case AV_OPT_TYPE_RATIONAL:
            return "rational";
        case AV_OPT_TYPE_BINARY:
            return "binary";
        case AV_OPT_TYPE_DICT:
            return "dictionary";
        case AV_OPT_TYPE_UINT64:
            return "unsigned64";
        case AV_OPT_TYPE_IMAGE_SIZE:
            return "size";
        case AV_OPT_TYPE_PIXEL_FMT:
            return "pixel-format";
        case AV_OPT_TYPE_SAMPLE_FMT:
            return "sample-format";
        case AV_OPT_TYPE_VIDEO_RATE:
            return "frame-rate";
        case AV_OPT_TYPE_DURATION:
            return "duration";
        case AV_OPT_TYPE_COLOR:
            return "color";
        case AV_OPT_TYPE_BOOL:
            return "boolean";
#if LIBAVUTIL_VERSION_MAJOR >= 57
        case AV_OPT_TYPE_CHLAYOUT:
#else
        case AV_OPT_TYPE_CHANNEL_LAYOUT:
#endif
            return "channel-layout";
#if LIBAVUTIL_VERSION_MAJOR >= 60
        case AV_OPT_TYPE_UINT:
            return "unsigned";
#endif
        default:
            return "value";
        }
    }
 
    bool option_has_numeric_range(AVOptionType type) {
        const int base_type = option_base_type(type);
        return base_type == AV_OPT_TYPE_FLAGS || base_type == AV_OPT_TYPE_INT || base_type == AV_OPT_TYPE_INT64 || base_type == AV_OPT_TYPE_DOUBLE || base_type == AV_OPT_TYPE_FLOAT || base_type == AV_OPT_TYPE_UINT64 || base_type == AV_OPT_TYPE_BOOL
#if LIBAVUTIL_VERSION_MAJOR >= 60
               || base_type == AV_OPT_TYPE_UINT
#endif
            ;
    }
 
    std::string number_text(double value) {
        std::ostringstream stream;
        stream << std::setprecision(12) << value;
        return stream.str();
    }
 
    void append_encoder_options(void *object, std::vector<EncoderOptionInfo> &result, std::set<std::string> &seen) {
        if (!object) {
            return;
        }
        for (const AVOption *option = nullptr; (option = av_opt_next(object, option));) {
            if (option->type == AV_OPT_TYPE_CONST || (option->flags & AV_OPT_FLAG_ENCODING_PARAM) == 0 || (option->flags & AV_OPT_FLAG_VIDEO_PARAM) == 0 || (option->flags & (AV_OPT_FLAG_READONLY | AV_OPT_FLAG_DEPRECATED)) != 0 || !option->name || !seen.insert(option->name).second) {
                continue;
            }
 
            EncoderOptionInfo info;
            info.name = option->name;
            info.type = option_type_name(option->type);
            info.help = option->help ? option->help : "";
            if (option_has_numeric_range(option->type)) {
                info.minimum = number_text(option->min);
                info.maximum = number_text(option->max);
            }
 
            uint8_t *value = nullptr;
            if (av_opt_get(object, option->name, 0, &value) >= 0 && value) {
                info.default_value = reinterpret_cast<char *>(value);
            }
            av_free(value);
 
            if (option->unit) {
                std::vector<std::string> choices;
                for (const AVOption *choice = nullptr; (choice = av_opt_next(object, choice));) {
                    if (choice->type == AV_OPT_TYPE_CONST && choice->unit && choice->name && std::string_view(choice->unit) == option->unit) {
                        choices.emplace_back(choice->name);
                    }
                }
                for (size_t index = 0; index < choices.size(); ++index) {
                    if (index > 0) {
                        info.choices += ", ";
                    }
                    info.choices += choices[index];
                }
            }
            result.push_back(std::move(info));
        }
    }
 
} // namespace
 
std::vector<EncoderInfo> available_video_encoders() {
    std::vector<EncoderInfo> result;
    void *iterator = nullptr;
    while (const AVCodec *codec = av_codec_iterate(&iterator)) {
        if (!av_codec_is_encoder(codec) || codec->type != AVMEDIA_TYPE_VIDEO || !codec->name) {
            continue;
        }
        EncoderInfo info;
        info.name = codec->name;
        info.long_name = codec->long_name ? codec->long_name : codec->name;
        info.codec_name = avcodec_get_name(codec->id);
        info.hardware = codec_uses_hardware(codec);
        info.experimental = (codec->capabilities & AV_CODEC_CAP_EXPERIMENTAL) != 0;
        const std::vector<AVPixelFormat> formats = supported_pixel_formats(codec);
        for (AVPixelFormat format : formats) {
            const char *name = av_get_pix_fmt_name(format);
            if (!name) {
                continue;
            }
            if (!info.pixel_formats.empty()) {
                info.pixel_formats += ", ";
            }
            info.pixel_formats += name;
        }
        result.push_back(std::move(info));
    }
    std::sort(result.begin(), result.end(), [](const EncoderInfo &left, const EncoderInfo &right) {
        if (left.codec_name != right.codec_name) {
            return left.codec_name < right.codec_name;
        }
        if (left.hardware != right.hardware) {
            return left.hardware > right.hardware;
        }
        return left.name < right.name;
    });
    return result;
}
 
std::vector<EncoderOptionInfo> video_encoder_options(std::string_view encoder_name) {
    const std::string name(encoder_name);
    const AVCodec *codec = avcodec_find_encoder_by_name(name.c_str());
    if (!codec || codec->type != AVMEDIA_TYPE_VIDEO) {
        return {};
    }
    AVCodecContext *context = avcodec_alloc_context3(codec);
    if (!context) {
        return {};
    }
    std::vector<EncoderOptionInfo> result;
    std::set<std::string> seen;
    append_encoder_options(context->priv_data, result, seen);
    append_encoder_options(context, result, seen);
    avcodec_free_context(&context);
    std::sort(result.begin(), result.end(), [](const EncoderOptionInfo &left, const EncoderOptionInfo &right) { return left.name < right.name; });
    return result;
}
 
bool Writer::open(const std::string &filename, int w, int h, float fps, const char *crf) {
    std::lock_guard<std::mutex> lock(writer_mutex);
    EncodeOptions opts;
    if (crf && *crf) {
        try {
            opts.crf = std::stoi(crf);
        } catch (...) {
        }
    }
    // Preserve legacy low-latency behaviour for old callers.
    opts.preset = "ultrafast";
    opts.tune = "zerolatency";
    opts.realtime = true;
    return openInternal(filename, w, h, fps, opts, false);
}
 
bool Writer::open(const std::string &filename, int w, int h, float fps, const EncodeOptions &opts) {
    std::lock_guard<std::mutex> lock(writer_mutex);
    return openInternal(filename, w, h, fps, opts, false);
}
 
bool Writer::open_ts(const std::string &filename, int w, int h, float fps, const char *crf) {
    std::lock_guard<std::mutex> lock(writer_mutex);
    EncodeOptions opts;
    if (crf && *crf) {
        try {
            opts.crf = std::stoi(crf);
        } catch (...) {
        }
    }
    opts.preset = "ultrafast";
    opts.tune = "zerolatency";
    opts.realtime = true;
    return openInternal(filename, w, h, fps, opts, true);
}
 
bool Writer::open_ts(const std::string &filename, int w, int h, float fps, const EncodeOptions &opts) {
    std::lock_guard<std::mutex> lock(writer_mutex);
    return openInternal(filename, w, h, fps, opts, true);
}
 
bool Writer::initHardwareEncoding(const AVCodec *codec, AVPixelFormat requested_format, bool prefer_cuda_rgba) {
    const AVCodecHWConfig *hardware_config = nullptr;
    for (int index = 0; const AVCodecHWConfig *config = avcodec_get_hw_config(codec, index); ++index) {
        if ((config->methods & AV_CODEC_HW_CONFIG_METHOD_HW_FRAMES_CTX) == 0 || config->device_type == AV_HWDEVICE_TYPE_NONE || config->pix_fmt == AV_PIX_FMT_NONE) {
            continue;
        }
        if (!hardware_config || (prefer_cuda_rgba && config->device_type == AV_HWDEVICE_TYPE_CUDA)) {
            hardware_config = config;
        }
        if (prefer_cuda_rgba && config->device_type == AV_HWDEVICE_TYPE_CUDA) {
            break;
        }
    }
    if (!hardware_config || av_hwdevice_ctx_create(&hw_device_ctx, hardware_config->device_type, nullptr, nullptr, 0) < 0) {
        return false;
    }
 
    codec_ctx->hw_device_ctx = av_buffer_ref(hw_device_ctx);
    codec_ctx->pix_fmt = hardware_config->pix_fmt;
 
    hw_frames_ctx = av_hwframe_ctx_alloc(hw_device_ctx);
    if (!hw_frames_ctx) {
        return false;
    }
 
    auto *frames_ctx = reinterpret_cast<AVHWFramesContext *>(hw_frames_ctx->data);
    frames_ctx->format = hardware_config->pix_fmt;
 
    AVHWFramesConstraints *constraints = av_hwdevice_get_hwframe_constraints(hw_device_ctx, nullptr);
    auto valid_software_format = [constraints](AVPixelFormat format) {
        if (format == AV_PIX_FMT_NONE || is_hardware_pixel_format(format) || !sws_isSupportedOutput(format)) {
            return false;
        }
        if (!constraints || !constraints->valid_sw_formats) {
            return true;
        }
        for (const AVPixelFormat *valid = constraints->valid_sw_formats; *valid != AV_PIX_FMT_NONE; ++valid) {
            if (*valid == format) {
                return true;
            }
        }
        return false;
    };
 
    AVPixelFormat upload_format = AV_PIX_FMT_NONE;
    if (prefer_cuda_rgba && valid_software_format(AV_PIX_FMT_RGBA)) {
        upload_format = AV_PIX_FMT_RGBA;
    } else if (valid_software_format(requested_format)) {
        upload_format = requested_format;
    } else {
        static constexpr AVPixelFormat preferred_upload_formats[] = {AV_PIX_FMT_NV12, AV_PIX_FMT_YUV420P, AV_PIX_FMT_P010LE, AV_PIX_FMT_YUV420P10LE, AV_PIX_FMT_YUV422P, AV_PIX_FMT_BGRA, AV_PIX_FMT_RGBA};
        for (AVPixelFormat format : preferred_upload_formats) {
            if (valid_software_format(format)) {
                upload_format = format;
                break;
            }
        }
        if (upload_format == AV_PIX_FMT_NONE && constraints && constraints->valid_sw_formats) {
            for (const AVPixelFormat *valid = constraints->valid_sw_formats; *valid != AV_PIX_FMT_NONE; ++valid) {
                if (valid_software_format(*valid)) {
                    upload_format = *valid;
                    break;
                }
            }
        }
    }
    av_hwframe_constraints_free(&constraints);
    if (upload_format == AV_PIX_FMT_NONE) {
        return false;
    }
 
    frames_ctx->sw_format = upload_format;
    frames_ctx->width = width;
    frames_ctx->height = height;
    // Pool must comfortably exceed MAX_QUEUE_SIZE so av_hwframe_get_buffer()
    // on the producer thread never becomes the throttle.  A few extra slots
    // cover frames currently in-flight inside the encoder.
    frames_ctx->initial_pool_size = static_cast<int>(MAX_QUEUE_SIZE) + 8;
 
    if (av_hwframe_ctx_init(hw_frames_ctx) < 0) {
        return false;
    }
 
    codec_ctx->hw_frames_ctx = av_buffer_ref(hw_frames_ctx);
    codec_ctx->sw_pix_fmt = upload_format;
 
    upload_sw_frame = av_frame_alloc();
    if (!upload_sw_frame) {
        return false;
    }
    upload_sw_frame->format = upload_format;
    upload_sw_frame->width = width;
    upload_sw_frame->height = height;
    if (av_frame_get_buffer(upload_sw_frame, 32) < 0) {
        return false;
    }
 
    if (upload_format != AV_PIX_FMT_RGBA) {
        sws_ctx = sws_getContext(width, height, AV_PIX_FMT_RGBA, width, height, upload_format, SWS_FAST_BILINEAR, nullptr, nullptr, nullptr);
        if (!sws_ctx) {
            return false;
        }
    }
 
    direct_cuda_upload = hardware_config->device_type == AV_HWDEVICE_TYPE_CUDA && upload_format == AV_PIX_FMT_RGBA;
 
#ifdef MXWRITE_HAS_CUDA_COPY
    // Non-blocking stream so device-to-device uploads from write_cuda_rgba()
    // do not serialise against the renderer's CUDA work on the default stream.
    if (direct_cuda_upload && !cuda_upload_stream) {
        if (cudaStreamCreateWithFlags(&cuda_upload_stream, cudaStreamNonBlocking) != cudaSuccess) {
            cuda_upload_stream = nullptr;
        }
    }
#endif
 
    return true;
}
 
bool Writer::openInternal(const std::string &filename, int w, int h, float fps, const EncodeOptions &opts, bool ts_mode) {
    avformat_network_init();
    av_log_set_level(AV_LOG_ERROR);
    opened = false;
    active_encoder_hardware = false;
    stop_requested = false;
    frame_count = 0;
    last_duration = 0.0;
    bytes_written.store(0, std::memory_order_relaxed);
    block_when_full.store(opts.block_when_full, std::memory_order_relaxed);
 
    while (!encode_queue.empty()) {
        releaseFrame(encode_queue.front());
        encode_queue.pop();
    }
 
    std::vector<FfmpegOption> extra_options;
    if (!opts.ffmpeg_options.empty() && !parse_ffmpeg_options(opts.ffmpeg_options, extra_options)) {
        return false;
    }
 
    const std::string *codec_override = find_ffmpeg_option(extra_options, "c");
    if (!codec_override) {
        codec_override = find_ffmpeg_option(extra_options, "codec");
    }
    if (!codec_override) {
        codec_override = find_ffmpeg_option(extra_options, "vcodec");
    }
 
    const std::string *pixel_format_option = find_ffmpeg_option(extra_options, "pix_fmt");
    if (!pixel_format_option) {
        pixel_format_option = find_ffmpeg_option(extra_options, "pixel_format");
    }
    AVPixelFormat requested_pixel_format = AV_PIX_FMT_NONE;
    if (pixel_format_option) {
        requested_pixel_format = av_get_pix_fmt(pixel_format_option->c_str());
        if (requested_pixel_format == AV_PIX_FMT_NONE) {
            std::cerr << "MXWrite: unknown pixel format '" << *pixel_format_option << "'.\n";
            return false;
        }
    }
 
    // Pass nullptr for format_name so libavformat picks the container based
    // on the filename extension (mp4, mkv, mov, avi...).
    if (avformat_alloc_output_context2(&format_ctx, nullptr, nullptr, filename.c_str()) < 0) {
        std::cerr << "Could not allocate output context.\n";
        return false;
    }
 
    width = w;
    height = h;
    hdr_output = opts.hdr.enabled;
    hdr_info = opts.hdr;
 
    // ---- HDR (HEVC Main10 + BT.2020/PQ) path ------------------------------
    // Short-circuits the normal SDR codec selection when opts.hdr.enabled is
    // true. Forces software libx265 + YUV420P10LE + PQ metadata, writes the
    // color tags and mastering/content-light side data, and bypasses NVENC.
    if (hdr_output) {
        const AVCodec *hdr_codec = avcodec_find_encoder_by_name("libx265");
        if (!hdr_codec) {
            std::cerr << "MXWrite: HDR output requested but libx265 encoder not available.\n";
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
 
        stream = avformat_new_stream(format_ctx, hdr_codec);
        if (!stream) {
            std::cerr << "MXWrite: could not create HDR stream.\n";
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
 
        calculateFPSFraction(fps, fps_num, fps_den);
        AVRational tb_hdr = {fps_den, fps_num};
        stream->time_base = tb_hdr;
 
        codec_ctx = avcodec_alloc_context3(hdr_codec);
        if (!codec_ctx) {
            std::cerr << "MXWrite: could not allocate HDR codec context.\n";
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
 
        codec_ctx->width = width;
        codec_ctx->height = height;
        codec_ctx->time_base = stream->time_base;
        codec_ctx->framerate = AVRational{fps_num, fps_den};
        codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P10LE;
        codec_ctx->profile = AV_PROFILE_HEVC_MAIN_10;
        codec_ctx->bits_per_raw_sample = 10;
        codec_ctx->gop_size = 30;
        codec_ctx->max_b_frames = 0;
        codec_ctx->thread_count = std::max(1u, std::thread::hardware_concurrency());
        codec_ctx->thread_type = FF_THREAD_SLICE;
        codec_ctx->delay = 0;
        codec_ctx->bit_rate = std::max<std::int64_t>(0, opts.bit_rate);
 
        // Tag the stream with BT.2020 + PQ (or whatever the input used).
        codec_ctx->color_primaries = static_cast<AVColorPrimaries>(hdr_info.color_primaries ? hdr_info.color_primaries : AVCOL_PRI_BT2020);
        codec_ctx->color_trc = static_cast<AVColorTransferCharacteristic>(hdr_info.color_trc ? hdr_info.color_trc : AVCOL_TRC_SMPTE2084);
        codec_ctx->colorspace = static_cast<AVColorSpace>(hdr_info.color_space ? hdr_info.color_space : AVCOL_SPC_BT2020_NCL);
        codec_ctx->color_range = static_cast<AVColorRange>(hdr_info.color_range ? hdr_info.color_range : AVCOL_RANGE_MPEG);
        codec_ctx->chroma_sample_location = AVCHROMA_LOC_LEFT;
 
        // Encoder options: Main10, matching x265-params for color volume.
        std::string preset_hdr = opts.preset.empty() ? std::string("medium") : opts.preset;
        av_opt_set(codec_ctx->priv_data, "preset", preset_hdr.c_str(), 0);
        if (opts.bit_rate <= 0) {
            int crf_val_hdr = opts.crf;
            if (crf_val_hdr < 0)
                crf_val_hdr = 0;
            if (crf_val_hdr > 51)
                crf_val_hdr = 51;
            const std::string crf_hdr = std::to_string(crf_val_hdr);
            av_opt_set(codec_ctx->priv_data, "crf", crf_hdr.c_str(), 0);
        }
 
        // x265 params: colorprim, transfer, colormatrix, range, hdr flag.
        // These drive the stream VUI + SEI so players recognise the file as HDR.
        std::string x265_params = "profile=main10:colorprim=bt2020:transfer=smpte2084:colormatrix=bt2020nc:range=limited:repeat-headers=1";
        // When HLG transfer is requested, swap transfer + mark hlg.
        if (codec_ctx->color_trc == AVCOL_TRC_ARIB_STD_B67) {
            x265_params = "profile=main10:colorprim=bt2020:transfer=arib-std-b67:colormatrix=bt2020nc:range=limited:repeat-headers=1";
        }
        av_opt_set(codec_ctx->priv_data, "x265-params", x265_params.c_str(), 0);
 
        if (pixel_format_option && requested_pixel_format != AV_PIX_FMT_YUV420P10LE) {
            std::cerr << "MXWrite: HDR output forces yuv420p10le; ignoring requested pixel format '" << *pixel_format_option << "'.\n";
        }
        if (!apply_ffmpeg_options(extra_options, codec_ctx, format_ctx)) {
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
 
        time_base = tb_hdr;
        if (format_ctx->oformat->flags & AVFMT_GLOBALHEADER) {
            codec_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
        }
        if (avcodec_open2(codec_ctx, hdr_codec, nullptr) < 0) {
            std::cerr << "MXWrite: could not open libx265 for HDR output.\n";
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
        if (avcodec_parameters_from_context(stream->codecpar, codec_ctx) < 0) {
            std::cerr << "MXWrite: could not copy HDR codec parameters.\n";
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
 
        // Attach mastering-display / content-light side data to the stream
        // codec parameters. Uses the modern AVCodecParameters coded_side_data
        // API. Failures are logged but non-fatal.
        auto attach_side = [&](AVPacketSideDataType type, const std::vector<uint8_t> &payload) {
            if (payload.empty())
                return;
            uint8_t *buf = static_cast<uint8_t *>(av_malloc(payload.size()));
            if (!buf)
                return;
            std::memcpy(buf, payload.data(), payload.size());
            const AVPacketSideData *added = av_packet_side_data_add(&stream->codecpar->coded_side_data, &stream->codecpar->nb_coded_side_data, type, buf, payload.size(), 0);
            if (!added) {
                av_free(buf);
                std::cerr << "MXWrite: failed to attach HDR side data (type " << (int)type << ").\n";
            }
        };
        attach_side(AV_PKT_DATA_MASTERING_DISPLAY_METADATA, hdr_info.mastering_display);
        attach_side(AV_PKT_DATA_CONTENT_LIGHT_LEVEL, hdr_info.content_light);
 
        if (!(format_ctx->oformat->flags & AVFMT_NOFILE)) {
            if (avio_open(&format_ctx->pb, filename.c_str(), AVIO_FLAG_WRITE) < 0) {
                std::cerr << "MXWrite: could not open HDR output file: " << filename << "\n";
                avcodec_free_context(&codec_ctx);
                avformat_free_context(format_ctx);
                format_ctx = nullptr;
                return false;
            }
        }
        if (avformat_write_header(format_ctx, nullptr) < 0) {
            std::cerr << "MXWrite: error writing HDR MP4 header.\n";
            avio_closep(&format_ctx->pb);
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
        updateBytesWritten();
 
        // Allocate the 10-bit YUV staging frame used by encodeAndWriteFrame.
        frame10 = av_frame_alloc();
        if (!frame10) {
            std::cerr << "MXWrite: could not allocate YUV420P10LE frame.\n";
            avio_closep(&format_ctx->pb);
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
        frame10->format = AV_PIX_FMT_YUV420P10LE;
        frame10->width = width;
        frame10->height = height;
        if (av_frame_get_buffer(frame10, 32) < 0) {
            std::cerr << "MXWrite: could not allocate YUV420P10LE buffer.\n";
            av_frame_free(&frame10);
            avio_closep(&format_ctx->pb);
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
 
        opened = true;
        use_hw_encode = false;
        recordingStart = std::chrono::steady_clock::now();
        startEncoderThread();
        std::cout << "MXWrite: HDR output active (libx265 Main10, BT.2020, " << (codec_ctx->color_trc == AVCOL_TRC_ARIB_STD_B67 ? "HLG" : "PQ") << ")\n";
        return true;
    }
    // ---- End HDR path -----------------------------------------------------
 
    const bool is_high_res = (width > 3840 || height > 2160);
    std::string codec_pref = lowercase_ascii(codec_override ? *codec_override : opts.codec);
    if (codec_pref.empty()) {
        codec_pref = "auto";
    }
    const bool explicit_hevc_nvenc = (codec_pref == "hevc_nvenc" || codec_pref == "h265_nvenc");
    const bool explicit_h264_nvenc = (codec_pref == "h264_nvenc");
    const bool explicit_hevc_software = (codec_pref == "hevc" || codec_pref == "h265" || codec_pref == "libx265");
    const bool explicit_h264_software = (codec_pref == "h264" || codec_pref == "libx264");
    const bool use_hevc_codec = explicit_hevc_nvenc || explicit_hevc_software || (!explicit_h264_nvenc && !explicit_h264_software && is_high_res);
    std::string hw_codec_name = use_hevc_codec ? "hevc_nvenc" : "h264_nvenc";
    AVCodecID sw_codec_id = use_hevc_codec ? AV_CODEC_ID_HEVC : AV_CODEC_ID_H264;
 
    // Codec selection based on user preference.
    const AVCodec *codec = nullptr;
    bool wants_hw = false;
    if (codec_pref == "software" || codec_pref == "x264" || codec_pref == "cpu" || explicit_hevc_software || explicit_h264_software) {
        if (codec_pref == "libx264" || codec_pref == "libx265") {
            codec = avcodec_find_encoder_by_name(codec_pref.c_str());
        } else {
            codec = avcodec_find_encoder(sw_codec_id);
        }
        wants_hw = false;
    } else if (codec_pref == "auto" || codec_pref == "nvenc" || explicit_hevc_nvenc || explicit_h264_nvenc) {
        // "auto" or "nvenc" keeps the resolution-based default; concrete
        // names like "hevc_nvenc" and "h264_nvenc" select that NVENC codec.
        codec = avcodec_find_encoder_by_name(hw_codec_name.c_str());
        wants_hw = (codec != nullptr);
        if (!codec) {
            if (codec_pref == "nvenc" || explicit_hevc_nvenc || explicit_h264_nvenc) {
                std::cerr << "MXWrite: NVENC requested but " << hw_codec_name << " not available; falling back to software.\n";
            }
            codec = avcodec_find_encoder(sw_codec_id);
        }
    } else {
        // Concrete FFmpeg encoder names are kept distinct. This permits all
        // linked encoders that accept system-memory frames (for example AV1,
        // VP9, ProRes, FFV1, QSV, AMF, VideoToolbox, and V4L2 M2M) instead of
        // collapsing the request to the default H.264 encoder.
        codec = avcodec_find_encoder_by_name(codec_pref.c_str());
        wants_hw = codec && (codec_pref.ends_with("_nvenc"));
        if (wants_hw) {
            hw_codec_name = codec_pref;
            sw_codec_id = codec->id;
        }
    }
 
    if (!codec) {
        std::cerr << "MXWrite: could not find requested video encoder '" << codec_pref << "'. Use acmx2 --list-encoders to see this FFmpeg build.\n";
        avformat_free_context(format_ctx);
        format_ctx = nullptr;
        return false;
    }
 
    // Validate / sanitise preset and CRF.
    std::string preset = opts.preset.empty() ? std::string("medium") : opts.preset;
    if (!is_valid_x264_preset(preset)) {
        // Accept unknown names; forward as-is. If empty, medium.
    }
    int crf_val = opts.crf;
    if (crf_val < 0)
        crf_val = 0;
    if (crf_val > 51)
        crf_val = 51;
    const std::string crf_str = std::to_string(crf_val);
 
    stream = avformat_new_stream(format_ctx, codec);
    if (!stream) {
        std::cerr << "Could not create new stream.\n";
        avformat_free_context(format_ctx);
        format_ctx = nullptr;
        return false;
    }
 
    calculateFPSFraction(fps, fps_num, fps_den);
 
    AVRational tb = {fps_den, fps_num};
    stream->time_base = tb;
 
    codec_ctx = avcodec_alloc_context3(codec);
    if (!codec_ctx) {
        std::cerr << "Could not allocate codec context.\n";
        avformat_free_context(format_ctx);
        format_ctx = nullptr;
        return false;
    }
 
    codec_ctx->width = width;
    codec_ctx->height = height;
    codec_ctx->time_base = stream->time_base;
    codec_ctx->framerate = AVRational{fps_num, fps_den};
    AVPixelFormat software_pixel_format = choose_software_pixel_format(wants_hw ? avcodec_find_encoder(sw_codec_id) : codec, requested_pixel_format);
    const bool requires_hardware_frames = !wants_hw && software_pixel_format == AV_PIX_FMT_NONE && codec_uses_hardware(codec);
    if (software_pixel_format == AV_PIX_FMT_NONE && !requires_hardware_frames) {
        const char *requested_name = requested_pixel_format == AV_PIX_FMT_NONE ? "an automatic system-memory format" : av_get_pix_fmt_name(requested_pixel_format);
        std::cerr << "MXWrite: encoder '" << codec->name << "' does not accept " << (requested_name ? requested_name : "the requested pixel format")
                  << " that MXWrite can convert from RGBA. Choose a supported -pix_fmt; "
                     "hardware-frame-only encoders require a device-specific upload path.\n";
        avcodec_free_context(&codec_ctx);
        avformat_free_context(format_ctx);
        format_ctx = nullptr;
        return false;
    }
    codec_ctx->pix_fmt = wants_hw ? AV_PIX_FMT_CUDA : software_pixel_format;
    codec_ctx->gop_size = 30;
    codec_ctx->max_b_frames = 0;
    codec_ctx->thread_count = std::max(1u, std::thread::hardware_concurrency());
    // Frame threading scales much better than slice threading for x264 when
    // latency is not a concern; switch only to slice threading in realtime/ts.
    if (ts_mode || opts.realtime) {
        codec_ctx->thread_type = FF_THREAD_SLICE;
        codec_ctx->slices = 4;
    } else {
        codec_ctx->thread_type = FF_THREAD_FRAME | FF_THREAD_SLICE;
    }
    codec_ctx->delay = 0;
    codec_ctx->bit_rate = std::max<std::int64_t>(0, opts.bit_rate);
 
    if (ts_mode || opts.realtime) {
        codec_ctx->flags |= AV_CODEC_FLAG_LOW_DELAY;
    }
 
    bool extra_options_applied = false;
    bool fell_back_from_hardware = false;
    if (requires_hardware_frames) {
        set_named_encoder_option(codec_ctx->priv_data, "preset", preset);
        if (!opts.tune.empty() && opts.tune != "none") {
            set_named_encoder_option(codec_ctx->priv_data, "tune", opts.tune);
        }
        if (opts.bit_rate <= 0) {
            set_named_encoder_option(codec_ctx->priv_data, "crf", crf_str);
        }
        if (!apply_ffmpeg_options(extra_options, codec_ctx, format_ctx)) {
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
        extra_options_applied = true;
        if (!initHardwareEncoding(codec, requested_pixel_format, false)) {
            std::cerr << "MXWrite: encoder '" << codec->name
                      << "' requires hardware frames, but its FFmpeg hardware device "
                         "could not be initialized.\n";
            av_buffer_unref(&hw_frames_ctx);
            av_buffer_unref(&hw_device_ctx);
            av_frame_free(&upload_sw_frame);
            sws_freeContext(sws_ctx);
            sws_ctx = nullptr;
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
        use_hw_encode = true;
        std::cout << "MXWrite: hardware encoder selected (" << codec->name << ")\n";
    }
    if (wants_hw) {
        const char *nv_preset = x264_preset_to_nvenc(preset);
        av_opt_set(codec_ctx->priv_data, "preset", nv_preset, 0);
        // NVENC "tune": hq (high quality), ll (low latency), ull (ultra low latency), lossless.
        const std::string requested_tune = lowercase_ascii(opts.tune);
        const std::string nv_tune = opts.realtime ? std::string("ll") : (is_nvenc_tune(requested_tune) ? requested_tune : std::string("hq"));
        av_opt_set(codec_ctx->priv_data, "tune", nv_tune.c_str(), 0);
        const std::string *custom_tune = find_ffmpeg_option(extra_options, "tune");
        const bool lossless_tune = nv_tune == "lossless" || (custom_tune && lowercase_ascii(*custom_tune) == "lossless");
        if (!lossless_tune) {
            av_opt_set(codec_ctx->priv_data, "rc", "vbr", 0);
            if (opts.bit_rate <= 0) {
                av_opt_set(codec_ctx->priv_data, "cq", crf_str.c_str(), 0);
            }
        }
        if (opts.realtime) {
            av_opt_set(codec_ctx->priv_data, "zerolatency", "1", 0);
        }
        if (use_hevc_codec) {
            av_opt_set(codec_ctx->priv_data, "tier", "high", 0);
        }
 
        if (requested_pixel_format == AV_PIX_FMT_YUV444P) {
            if (av_opt_set(codec_ctx->priv_data, "rgb_mode", "yuv444", 0) < 0) {
                std::cerr << "MXWrite: this NVENC build cannot convert RGBA input to yuv444p.\n";
                avcodec_free_context(&codec_ctx);
                avformat_free_context(format_ctx);
                format_ctx = nullptr;
                return false;
            }
            if (!find_ffmpeg_option(extra_options, "profile")) {
                const char *profile = use_hevc_codec ? "rext" : "high444p";
                av_opt_set(codec_ctx->priv_data, "profile", profile, 0);
            }
        } else if (requested_pixel_format != AV_PIX_FMT_NONE && requested_pixel_format != AV_PIX_FMT_YUV420P && requested_pixel_format != AV_PIX_FMT_RGBA) {
            std::cerr << "MXWrite: NVENC RGBA ingestion supports custom -pix_fmt yuv420p, "
                         "yuv444p, or rgba; requested '"
                      << av_get_pix_fmt_name(requested_pixel_format) << "'.\n";
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
 
        if (!apply_ffmpeg_options(extra_options, codec_ctx, format_ctx)) {
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
        extra_options_applied = true;
 
        if (initHardwareEncoding(codec, requested_pixel_format, true)) {
            use_hw_encode = true;
            std::cout << "MXWrite: hardware encoder selected (" << hw_codec_name << ")\n";
        } else {
            std::cerr << "MXWrite: " << hw_codec_name << " present but CUDA context failed, falling back to software encoder\n";
            fell_back_from_hardware = true;
            av_buffer_unref(&hw_frames_ctx);
            av_buffer_unref(&hw_device_ctx);
            av_frame_free(&upload_sw_frame);
            sws_freeContext(sws_ctx);
            sws_ctx = nullptr;
            direct_cuda_upload = false;
            avcodec_free_context(&codec_ctx);
 
            codec = avcodec_find_encoder(sw_codec_id);
            if (!codec) {
                std::cerr << "Could not find software fallback encoder.\n";
                avformat_free_context(format_ctx);
                format_ctx = nullptr;
                return false;
            }
 
            codec_ctx = avcodec_alloc_context3(codec);
            if (!codec_ctx) {
                std::cerr << "Could not allocate fallback codec context.\n";
                avformat_free_context(format_ctx);
                format_ctx = nullptr;
                return false;
            }
 
            codec_ctx->width = width;
            codec_ctx->height = height;
            codec_ctx->time_base = stream->time_base;
            codec_ctx->framerate = AVRational{fps_num, fps_den};
            codec_ctx->pix_fmt = software_pixel_format;
            codec_ctx->gop_size = 30;
            codec_ctx->max_b_frames = 0;
            codec_ctx->thread_count = std::max(1u, std::thread::hardware_concurrency());
            if (ts_mode || opts.realtime) {
                codec_ctx->thread_type = FF_THREAD_SLICE;
                codec_ctx->slices = 4;
            } else {
                codec_ctx->thread_type = FF_THREAD_FRAME | FF_THREAD_SLICE;
            }
            codec_ctx->delay = 0;
            codec_ctx->bit_rate = std::max<std::int64_t>(0, opts.bit_rate);
 
            if (ts_mode || opts.realtime) {
                codec_ctx->flags |= AV_CODEC_FLAG_LOW_DELAY;
            }
            extra_options_applied = false;
        }
    }
 
    if (!use_hw_encode) {
        const std::string software_preset = fell_back_from_hardware ? nvenc_preset_to_software(lowercase_ascii(preset)) : preset;
        set_named_encoder_option(codec_ctx->priv_data, "preset", software_preset);
        // Apply tune: realtime forces zerolatency; otherwise honour user value.
        std::string tune = opts.realtime ? std::string("zerolatency") : opts.tune;
        if (fell_back_from_hardware) {
            const std::string lowered_tune = lowercase_ascii(tune);
            if (lowered_tune == "hq" || lowered_tune == "uhq") {
                tune.clear();
            } else if (lowered_tune == "ll" || lowered_tune == "ull") {
                tune = "zerolatency";
            } else if (lowered_tune == "lossless") {
                tune.clear();
                if (use_hevc_codec) {
                    av_opt_set(codec_ctx->priv_data, "x265-params", "lossless=1", 0);
                } else {
                    av_opt_set(codec_ctx->priv_data, "qp", "0", 0);
                }
            }
        }
        if (!tune.empty() && tune != "none") {
            set_named_encoder_option(codec_ctx->priv_data, "tune", tune);
        }
        if (opts.bit_rate <= 0) {
            set_named_encoder_option(codec_ctx->priv_data, "crf", crf_str);
        }
        if (opts.realtime && codec->id == AV_CODEC_ID_H264) {
            // Legacy low-latency parameters kept for realtime path to avoid
            // pipeline stalls during live capture.
            av_opt_set(codec_ctx->priv_data, "x264-params", "bframes=0:ref=1:me=dia:subme=0", 0);
            av_opt_set(codec_ctx->priv_data, "force_cfr", "1", 0);
        }
    }
 
    const std::vector<FfmpegOption> translated_fallback_options = fell_back_from_hardware ? software_fallback_options(extra_options, use_hevc_codec) : std::vector<FfmpegOption>{};
    const std::vector<FfmpegOption> &options_to_apply = fell_back_from_hardware ? translated_fallback_options : extra_options;
    if (!extra_options_applied && !apply_ffmpeg_options(options_to_apply, codec_ctx, format_ctx)) {
        avcodec_free_context(&codec_ctx);
        avformat_free_context(format_ctx);
        format_ctx = nullptr;
        return false;
    }
 
    time_base = tb;
 
    if (format_ctx->oformat->flags & AVFMT_GLOBALHEADER) {
        codec_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    }
    if (avcodec_open2(codec_ctx, codec, nullptr) < 0) {
        std::cerr << "MXWrite: could not open encoder '" << codec->name << "'. The encoder may require unavailable hardware or options.\n";
        avcodec_free_context(&codec_ctx);
        avformat_free_context(format_ctx);
        format_ctx = nullptr;
        return false;
    }
    active_encoder_hardware = codec_uses_hardware(codec);
    if (avcodec_parameters_from_context(stream->codecpar, codec_ctx) < 0) {
        std::cerr << "Could not copy codec parameters.\n";
        avcodec_free_context(&codec_ctx);
        avformat_free_context(format_ctx);
        format_ctx = nullptr;
        return false;
    }
    if (!(format_ctx->oformat->flags & AVFMT_NOFILE)) {
        if (avio_open(&format_ctx->pb, filename.c_str(), AVIO_FLAG_WRITE) < 0) {
            std::cerr << "Could not open output file: " << filename << "\n";
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
    }
    if (avformat_write_header(format_ctx, nullptr) < 0) {
        std::cerr << "Error writing MP4 header.\n";
        avio_closep(&format_ctx->pb);
        avcodec_free_context(&codec_ctx);
        avformat_free_context(format_ctx);
        format_ctx = nullptr;
        return false;
    }
    updateBytesWritten();
 
    if (!use_hw_encode) {
        frameYUV = av_frame_alloc();
        if (!frameYUV) {
            std::cerr << "Could not allocate YUV frame.\n";
            avio_closep(&format_ctx->pb);
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
        frameYUV->format = software_pixel_format;
        frameYUV->width = width;
        frameYUV->height = height;
        if (av_frame_get_buffer(frameYUV, 32) < 0) {
            std::cerr << "Could not allocate frame buffer for YUV frame.\n";
            av_frame_free(&frameYUV);
            avio_closep(&format_ctx->pb);
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
 
        sws_ctx = sws_getContext(width, height, AV_PIX_FMT_RGBA, width, height, software_pixel_format, SWS_FAST_BILINEAR, nullptr, nullptr, nullptr);
        if (!sws_ctx) {
            std::cerr << "Could not initialize conversion context.\n";
            av_frame_free(&frameYUV);
            avio_closep(&format_ctx->pb);
            avcodec_free_context(&codec_ctx);
            avformat_free_context(format_ctx);
            format_ctx = nullptr;
            return false;
        }
    }
 
    opened = true;
    recordingStart = std::chrono::steady_clock::now();
    startEncoderThread();
    return true;
}
 
void Writer::write(void *rgba_buffer) { write_at_pts(rgba_buffer, AV_NOPTS_VALUE); }
 
void Writer::write_at_pts(void *rgba_buffer, int64_t pts) {
    if (!rgba_buffer) {
        return;
    }
 
    {
        std::lock_guard<std::mutex> lock(writer_mutex);
        if (!opened) {
            return;
        }
    }
 
    AVFrame *queued_frame = av_frame_alloc();
    if (!queued_frame) {
        std::cerr << "Writer: failed to allocate queued frame\n";
        return;
    }
 
    if (use_hw_encode && hdr_output) {
        queued_frame->format = codec_ctx->pix_fmt;
        queued_frame->width = width;
        queued_frame->height = height;
        if (av_hwframe_get_buffer(hw_frames_ctx, queued_frame, 0) < 0) {
            std::cerr << "Writer: failed to allocate frame from hardware pool\n";
            releaseFrame(queued_frame);
            return;
        }
 
        if (av_frame_make_writable(upload_sw_frame) < 0) {
            std::cerr << "Writer: software upload frame not writable\n";
            releaseFrame(queued_frame);
            return;
        }
 
        const auto *src = static_cast<const uint8_t *>(rgba_buffer);
        if (upload_sw_frame->format == AV_PIX_FMT_RGBA) {
            for (int y = 0; y < height; ++y) {
                std::memcpy(upload_sw_frame->data[0] + static_cast<size_t>(y) * upload_sw_frame->linesize[0], src + static_cast<size_t>(y) * static_cast<size_t>(width) * 4, static_cast<size_t>(width) * 4);
            }
        } else {
            const uint8_t *source_data[1] = {src};
            const int source_linesize[1] = {width * 4};
            sws_scale(sws_ctx, source_data, source_linesize, 0, height, upload_sw_frame->data, upload_sw_frame->linesize);
        }
 
        if (av_hwframe_transfer_data(queued_frame, upload_sw_frame, 0) < 0) {
            std::cerr << "Writer: failed to transfer system frame to hardware frame\n";
            releaseFrame(queued_frame);
            return;
        }
    } else {
        queued_frame->format = AV_PIX_FMT_RGBA;
        queued_frame->width = width;
        queued_frame->height = height;
        if (av_frame_get_buffer(queued_frame, 32) < 0) {
            std::cerr << "Writer: failed to allocate queued RGBA frame buffer\n";
            releaseFrame(queued_frame);
            return;
        }
        if (av_frame_make_writable(queued_frame) < 0) {
            std::cerr << "Writer: queued RGBA frame not writable\n";
            releaseFrame(queued_frame);
            return;
        }
 
        const auto *src = static_cast<const uint8_t *>(rgba_buffer);
        for (int y = 0; y < height; ++y) {
            std::memcpy(queued_frame->data[0] + static_cast<size_t>(y) * queued_frame->linesize[0], src + static_cast<size_t>(y) * static_cast<size_t>(width) * 4, static_cast<size_t>(width) * 4);
        }
    }
 
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        if (block_when_full.load(std::memory_order_relaxed)) {
            if (encode_queue.size() >= NO_DROP_QUEUE_SIZE) {
                // Keep file processing paced with the encoder. Wake whenever
                // one queue slot becomes available rather than waiting for a
                // large queue to fill and then drain completely.
                queue_cv.wait(lock, [this] { return stop_requested || encode_queue.size() < NO_DROP_QUEUE_SIZE; });
            }
            if (stop_requested) {
                releaseFrame(queued_frame);
                return;
            }
        } else if (stop_requested || encode_queue.size() >= MAX_QUEUE_SIZE) {
            static int drop_counter = 0;
            if (++drop_counter % 30 == 0) {
                std::cerr << "Writer: dropped " << drop_counter << " SDR frames (encoder queue full)\n";
            }
            releaseFrame(queued_frame);
            return;
        }
        if (pts != AV_NOPTS_VALUE && pts < frame_count) {
            // A timestamped live frame landed in a nominal frame slot that
            // was already filled. Drop it instead of extending the video
            // timeline and allowing it to drift behind the capture clock.
            releaseFrame(queued_frame);
            return;
        }
        queued_frame->pts = pts == AV_NOPTS_VALUE ? frame_count : pts;
        frame_count = queued_frame->pts + 1;
        encode_queue.push(queued_frame);
    }
 
    queue_cv.notify_one();
}
 
void Writer::write_hdr_rgba16(void *rgba16_buffer) { write_hdr_rgba16_at_pts(rgba16_buffer, AV_NOPTS_VALUE); }
 
void Writer::write_hdr_rgba16_at_pts(void *rgba16_buffer, int64_t pts) {
    if (!rgba16_buffer) {
        return;
    }
 
    {
        std::lock_guard<std::mutex> lock(writer_mutex);
        if (!opened) {
            return;
        }
        if (!hdr_output) {
            std::cerr << "Writer: write_hdr_rgba16 called but writer not in HDR mode\n";
            return;
        }
    }
 
    AVFrame *queued_frame = av_frame_alloc();
    if (!queued_frame) {
        std::cerr << "Writer: failed to allocate queued HDR frame\n";
        return;
    }
    queued_frame->format = AV_PIX_FMT_YUV420P10LE;
    queued_frame->width = width;
    queued_frame->height = height;
    if (av_frame_get_buffer(queued_frame, 32) < 0) {
        std::cerr << "Writer: failed to allocate YUV420P10 buffer\n";
        releaseFrame(queued_frame);
        return;
    }
    if (av_frame_make_writable(queued_frame) < 0) {
        std::cerr << "Writer: queued HDR frame not writable\n";
        releaseFrame(queued_frame);
        return;
    }
 
    // Convert the already-PQ/HLG-encoded 16-bit BT.2020 RGBA into the
    // 10-bit limited-range YUV420 plane that libx265 Main10 expects.
    convertBt2020Rgba16EncodedToYuv420p10(reinterpret_cast<const uint16_t *>(rgba16_buffer), width * 4, reinterpret_cast<uint16_t *>(queued_frame->data[0]), queued_frame->linesize[0] / 2, reinterpret_cast<uint16_t *>(queued_frame->data[1]), queued_frame->linesize[1] / 2, reinterpret_cast<uint16_t *>(queued_frame->data[2]), queued_frame->linesize[2] / 2, width, height);
 
    queued_frame->color_primaries = static_cast<AVColorPrimaries>(hdr_info.color_primaries ? hdr_info.color_primaries : AVCOL_PRI_BT2020);
    queued_frame->color_trc = static_cast<AVColorTransferCharacteristic>(hdr_info.color_trc ? hdr_info.color_trc : AVCOL_TRC_SMPTE2084);
    queued_frame->colorspace = static_cast<AVColorSpace>(hdr_info.color_space ? hdr_info.color_space : AVCOL_SPC_BT2020_NCL);
    queued_frame->color_range = static_cast<AVColorRange>(hdr_info.color_range ? hdr_info.color_range : AVCOL_RANGE_MPEG);
 
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        if (block_when_full.load(std::memory_order_relaxed)) {
            if (encode_queue.size() >= NO_DROP_QUEUE_SIZE) {
                queue_cv.wait(lock, [this] { return stop_requested || encode_queue.size() < NO_DROP_QUEUE_SIZE; });
            }
            if (stop_requested) {
                releaseFrame(queued_frame);
                return;
            }
        } else if (stop_requested || encode_queue.size() >= MAX_QUEUE_SIZE) {
            static int drop_counter = 0;
            if (++drop_counter % 30 == 0) {
                std::cerr << "Writer: dropped " << drop_counter << " HDR frames (encoder queue full)\n";
            }
            releaseFrame(queued_frame);
            return;
        }
        if (pts != AV_NOPTS_VALUE && pts < frame_count) {
            releaseFrame(queued_frame);
            return;
        }
        queued_frame->pts = pts == AV_NOPTS_VALUE ? frame_count : pts;
        frame_count = queued_frame->pts + 1;
        encode_queue.push(queued_frame);
    }
 
    queue_cv.notify_one();
}
 
bool Writer::write_cuda_rgba(void *cuda_rgba_buffer, int src_stride, [[maybe_unused]] bool bottom_up) { return write_cuda_rgba_at_pts(cuda_rgba_buffer, src_stride, AV_NOPTS_VALUE, bottom_up); }
 
bool Writer::write_cuda_rgba_at_pts(void *cuda_rgba_buffer, int src_stride, int64_t pts, [[maybe_unused]] bool bottom_up) {
    if (!cuda_rgba_buffer || src_stride <= 0) {
        return false;
    }
 
    {
        std::lock_guard<std::mutex> lock(writer_mutex);
        if (!opened || !use_hw_encode || !direct_cuda_upload) {
            return false;
        }
    }
 
    AVFrame *queued_frame = av_frame_alloc();
    if (!queued_frame) {
        std::cerr << "Writer: failed to allocate queued CUDA frame\n";
        return false;
    }
 
    queued_frame->format = AV_PIX_FMT_CUDA;
    queued_frame->width = width;
    queued_frame->height = height;
 
    if (av_hwframe_get_buffer(hw_frames_ctx, queued_frame, 0) < 0) {
        std::cerr << "Writer: failed to allocate CUDA frame from hardware pool\n";
        releaseFrame(queued_frame);
        return false;
    }
 
#ifdef MXWRITE_HAS_CUDA_COPY
    cudaStream_t stream = cuda_upload_stream;
    const bool use_async_stream = (stream != nullptr);
    if (!bottom_up) {
        const auto copy_err = use_async_stream ? cudaMemcpy2DAsync(queued_frame->data[0], static_cast<size_t>(queued_frame->linesize[0]), cuda_rgba_buffer, static_cast<size_t>(src_stride), static_cast<size_t>(width) * 4, static_cast<size_t>(height), cudaMemcpyDeviceToDevice, stream) : cudaMemcpy2D(queued_frame->data[0], static_cast<size_t>(queued_frame->linesize[0]), cuda_rgba_buffer, static_cast<size_t>(src_stride), static_cast<size_t>(width) * 4, static_cast<size_t>(height), cudaMemcpyDeviceToDevice);
 
        if (copy_err != cudaSuccess) {
            std::cerr << "Writer: cudaMemcpy2D device upload failed: " << cudaGetErrorString(copy_err) << "\n";
            releaseFrame(queued_frame);
            return false;
        }
    } else {
        // Flip vertically by issuing one async row copy per destination row
        // onto a single stream — kept asynchronous so launch overhead overlaps
        // and the producer thread only blocks once at cudaStreamSynchronize.
        auto *src_base = static_cast<unsigned char *>(cuda_rgba_buffer);
        auto *dst_base = queued_frame->data[0];
        const size_t row_bytes = static_cast<size_t>(width) * 4;
 
        for (int y = 0; y < height; ++y) {
            auto *src_row = src_base + static_cast<size_t>(height - 1 - y) * static_cast<size_t>(src_stride);
            auto *dst_row = dst_base + static_cast<size_t>(y) * static_cast<size_t>(queued_frame->linesize[0]);
            const auto row_copy_err = use_async_stream ? cudaMemcpyAsync(dst_row, src_row, row_bytes, cudaMemcpyDeviceToDevice, stream) : cudaMemcpy(dst_row, src_row, row_bytes, cudaMemcpyDeviceToDevice);
            if (row_copy_err != cudaSuccess) {
                std::cerr << "Writer: cudaMemcpy row upload failed: " << cudaGetErrorString(row_copy_err) << "\n";
                releaseFrame(queued_frame);
                return false;
            }
        }
    }
    // Single synchronisation point — NVENC requires the data to be ready when
    // avcodec_send_frame() reads it, and the encoder thread is decoupled by
    // the queue so this sync only serialises this one producer call.
    if (use_async_stream) {
        const auto sync_err = cudaStreamSynchronize(stream);
        if (sync_err != cudaSuccess) {
            std::cerr << "Writer: cudaStreamSynchronize failed: " << cudaGetErrorString(sync_err) << "\n";
            releaseFrame(queued_frame);
            return false;
        }
    }
#else
    std::cerr << "Writer: CUDA copy support disabled at build time\n";
    releaseFrame(queued_frame);
    return false;
#endif
 
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        if (block_when_full.load(std::memory_order_relaxed)) {
            if (encode_queue.size() >= NO_DROP_QUEUE_SIZE) {
                queue_cv.wait(lock, [this] { return stop_requested || encode_queue.size() < NO_DROP_QUEUE_SIZE; });
            }
            if (stop_requested) {
                releaseFrame(queued_frame);
                return false;
            }
        } else if (stop_requested || encode_queue.size() >= MAX_QUEUE_SIZE) {
            static int drop_counter = 0;
            if (++drop_counter % 30 == 0) {
                std::cerr << "Writer: dropped " << drop_counter << " frames (encoder queue full)\n";
            }
            releaseFrame(queued_frame);
            // Return TRUE so the producer does NOT fall back to the slow CPU
            // write() path — we already "handled" the frame (by dropping it).
            // Falling back would double-process every frame and double the drops.
            queue_cv.notify_one();
            return true;
        }
        if (pts != AV_NOPTS_VALUE && pts < frame_count) {
            releaseFrame(queued_frame);
            queue_cv.notify_one();
            return true;
        }
        queued_frame->pts = pts == AV_NOPTS_VALUE ? frame_count : pts;
        frame_count = queued_frame->pts + 1;
        encode_queue.push(queued_frame);
    }
 
    queue_cv.notify_one();
    return true;
}
 
void Writer::write_ts(void *rgba_buffer) { write(rgba_buffer); }
 
void Writer::startEncoderThread() {
    stop_requested = false;
    encode_thread = std::jthread([this](std::stop_token st) { encodeLoop(st); });
}
 
void Writer::stopEncoderThread() {
    {
        std::lock_guard<std::mutex> lock(queue_mutex);
        stop_requested = true;
    }
    queue_cv.notify_all();
 
    if (encode_thread.joinable()) {
        encode_thread.request_stop();
        encode_thread.join();
    }
}
 
void Writer::releaseFrame(AVFrame *f) {
    if (!f) {
        return;
    }
    av_frame_free(&f);
}
 
void Writer::drainEncoderPackets() {
    AVPacket *pkt = av_packet_alloc();
    if (!pkt) {
        std::cerr << "Writer: failed to allocate packet\n";
        return;
    }
 
    while (true) {
        int ret = avcodec_receive_packet(codec_ctx, pkt);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
            break;
        }
        if (ret < 0) {
            std::cerr << "Writer: error receiving packet: " << ret << "\n";
            break;
        }
 
        if (pkt->duration <= 0) {
            pkt->duration = 1;
        }
        av_packet_rescale_ts(pkt, codec_ctx->time_base, stream->time_base);
        pkt->stream_index = stream->index;
 
        if (av_interleaved_write_frame(format_ctx, pkt) < 0) {
            std::cerr << "Writer: error writing frame\n";
            av_packet_unref(pkt);
            break;
        }
        updateBytesWritten();
        av_packet_unref(pkt);
    }
 
    av_packet_free(&pkt);
}
 
void Writer::encodeAndWriteFrame(AVFrame *in_frame) {
    if (!in_frame) {
        return;
    }
 
    AVFrame *encode_frame = in_frame;
    AVFrame *uploaded_frame = nullptr;
    if (hdr_output) {
        if (in_frame->format == AV_PIX_FMT_YUV420P10LE) {
            // Frame has already been converted to BT.2020 PQ YUV420P10LE
            // by write_hdr_rgba16(). Use directly.
            encode_frame = in_frame;
        } else {
            // in_frame is RGBA 8-bit from the shader pipeline. Convert to BT.2020
            // PQ YUV420P10LE in frame10 and submit that instead.
            if (av_frame_make_writable(frame10) < 0) {
                std::cerr << "Writer: HDR frame not writable\n";
                return;
            }
            convertRgbaToBt2020PqYuv420p10(in_frame->data[0], in_frame->linesize[0], reinterpret_cast<uint16_t *>(frame10->data[0]), frame10->linesize[0] / 2, reinterpret_cast<uint16_t *>(frame10->data[1]), frame10->linesize[1] / 2, reinterpret_cast<uint16_t *>(frame10->data[2]), frame10->linesize[2] / 2, width, height);
            frame10->pts = in_frame->pts;
            frame10->color_primaries = static_cast<AVColorPrimaries>(hdr_info.color_primaries ? hdr_info.color_primaries : AVCOL_PRI_BT2020);
            frame10->color_trc = static_cast<AVColorTransferCharacteristic>(hdr_info.color_trc ? hdr_info.color_trc : AVCOL_TRC_SMPTE2084);
            frame10->colorspace = static_cast<AVColorSpace>(hdr_info.color_space ? hdr_info.color_space : AVCOL_SPC_BT2020_NCL);
            frame10->color_range = static_cast<AVColorRange>(hdr_info.color_range ? hdr_info.color_range : AVCOL_RANGE_MPEG);
            encode_frame = frame10;
        }
    } else if (use_hw_encode && in_frame->format == AV_PIX_FMT_RGBA) {
        uploaded_frame = av_frame_alloc();
        if (!uploaded_frame) {
            std::cerr << "Writer: failed to allocate hardware upload frame\n";
            return;
        }
        uploaded_frame->format = codec_ctx->pix_fmt;
        uploaded_frame->width = width;
        uploaded_frame->height = height;
        if (av_hwframe_get_buffer(hw_frames_ctx, uploaded_frame, 0) < 0) {
            std::cerr << "Writer: failed to allocate frame from hardware pool\n";
            releaseFrame(uploaded_frame);
            return;
        }
        if (av_frame_make_writable(upload_sw_frame) < 0) {
            std::cerr << "Writer: software upload frame not writable\n";
            releaseFrame(uploaded_frame);
            return;
        }
 
        if (upload_sw_frame->format == AV_PIX_FMT_RGBA) {
            for (int y = 0; y < height; ++y) {
                std::memcpy(upload_sw_frame->data[0] + static_cast<size_t>(y) * upload_sw_frame->linesize[0], in_frame->data[0] + static_cast<size_t>(y) * in_frame->linesize[0], static_cast<size_t>(width) * 4);
            }
        } else {
            const uint8_t *source_data[1] = {in_frame->data[0]};
            const int source_linesize[1] = {in_frame->linesize[0]};
            sws_scale(sws_ctx, source_data, source_linesize, 0, height, upload_sw_frame->data, upload_sw_frame->linesize);
        }
 
        if (av_hwframe_transfer_data(uploaded_frame, upload_sw_frame, 0) < 0) {
            std::cerr << "Writer: failed to transfer system frame to hardware frame\n";
            releaseFrame(uploaded_frame);
            return;
        }
        uploaded_frame->pts = in_frame->pts;
        encode_frame = uploaded_frame;
    } else if (!use_hw_encode) {
        const uint8_t *src_data[1] = {in_frame->data[0]};
        int src_linesize[1] = {in_frame->linesize[0]};
        sws_scale(sws_ctx, src_data, src_linesize, 0, height, frameYUV->data, frameYUV->linesize);
        frameYUV->pts = in_frame->pts;
        encode_frame = frameYUV;
    }
 
    int ret = avcodec_send_frame(codec_ctx, encode_frame);
    if (ret == AVERROR(EAGAIN)) {
        // Encoder output queue is full; drain and retry this frame once.
        drainEncoderPackets();
        ret = avcodec_send_frame(codec_ctx, encode_frame);
    }
    if (ret < 0) {
        std::cerr << "Writer: error sending frame to encoder: " << ret << "\n";
        releaseFrame(uploaded_frame);
        return;
    }
 
    drainEncoderPackets();
    releaseFrame(uploaded_frame);
}
 
void Writer::encodeLoop(std::stop_token stop_token) {
    while (true) {
        AVFrame *frame = nullptr;
        {
            std::unique_lock<std::mutex> lock(queue_mutex);
            queue_cv.wait(lock, [this, &stop_token]() { return stop_requested || stop_token.stop_requested() || !encode_queue.empty(); });
 
            if ((stop_requested || stop_token.stop_requested()) && encode_queue.empty()) {
                break;
            }
 
            frame = encode_queue.front();
            encode_queue.pop();
        }
        // Wake any producer blocked in write() waiting for queue space.
        queue_cv.notify_one();
 
        encodeAndWriteFrame(frame);
        releaseFrame(frame);
    };
 
    if (codec_ctx) {
        const int flush_ret = avcodec_send_frame(codec_ctx, nullptr);
        if (flush_ret >= 0) {
            drainEncoderPackets();
        }
    }
}
 
void Writer::updateBytesWritten() noexcept {
    if (!format_ctx || !format_ctx->pb) {
        return;
    }
 
    const int64_t position = avio_tell(format_ctx->pb);
    if (position >= 0) {
        bytes_written.store(static_cast<std::uint64_t>(position), std::memory_order_relaxed);
    }
}
 
void Writer::close() {
    std::lock_guard<std::mutex> lock(writer_mutex);
    if (!opened) {
        return;
    }
 
    stopEncoderThread();
 
    if (stream && codec_ctx && frame_count > 0) {
        stream->duration = av_rescale_q(frame_count, codec_ctx->time_base, stream->time_base);
    }
    if (fps_num > 0 && fps_den > 0) {
        last_duration = static_cast<double>(frame_count) * static_cast<double>(fps_den) / static_cast<double>(fps_num);
    } else if (stream && stream->duration > 0) {
        last_duration = static_cast<double>(stream->duration) * av_q2d(stream->time_base);
    }
 
    av_write_trailer(format_ctx);
    updateBytesWritten();
 
    if (!(format_ctx->oformat->flags & AVFMT_NOFILE)) {
        avio_closep(&format_ctx->pb);
    }
 
    av_frame_free(&frameRGBA);
    av_frame_free(&frameYUV);
    av_frame_free(&frame10);
    sws_freeContext(sws_ctx);
    av_frame_free(&upload_sw_frame);
#ifdef MXWRITE_HAS_CUDA_COPY
    // Destroy stream before tearing down FFmpeg CUDA device/frames contexts.
    if (cuda_upload_stream) {
        cudaStreamSynchronize(cuda_upload_stream);
        cudaStreamDestroy(cuda_upload_stream);
        cuda_upload_stream = nullptr;
    }
#endif
    avcodec_free_context(&codec_ctx);
    av_buffer_unref(&hw_frames_ctx);
    av_buffer_unref(&hw_device_ctx);
    avformat_free_context(format_ctx);
 
    while (!encode_queue.empty()) {
        releaseFrame(encode_queue.front());
        encode_queue.pop();
    }
    opened = false;
    format_ctx = nullptr;
    codec_ctx = nullptr;
    sws_ctx = nullptr;
    frameRGBA = nullptr;
    frameYUV = nullptr;
    frame10 = nullptr;
    upload_sw_frame = nullptr;
    use_hw_encode = false;
    active_encoder_hardware = false;
    direct_cuda_upload = false;
    hdr_output = false;
    stop_requested = false;
}
 
double Writer::get_duration() const {
    if (!opened && last_duration > 0.0) {
        return last_duration;
    }
    if (stream && stream->duration > 0) {
        return static_cast<double>(stream->duration) * av_q2d(stream->time_base);
    }
    if (fps_num > 0 && fps_den > 0) {
        return static_cast<double>(frame_count) * static_cast<double>(fps_den) / static_cast<double>(fps_num);
    }
    return 0.0;
}