ladybird/Libraries/LibMedia/FFmpeg/FFmpegDemuxer.cpp

/*
 * Copyright (c) 2025, Luke Wilde <luke@ladybird.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Math.h>
#include <AK/Stream.h>
#include <AK/Time.h>
#include <LibMedia/FFmpeg/FFmpegDemuxer.h>
#include <LibMedia/FFmpeg/FFmpegHelpers.h>

namespace Media::FFmpeg {

FFmpegDemuxer::FFmpegDemuxer(NonnullOwnPtr<SeekableStream> stream, NonnullOwnPtr<Media::FFmpeg::FFmpegIOContext> io_context)
    : m_stream(move(stream))
    , m_io_context(move(io_context))
{
}

FFmpegDemuxer::~FFmpegDemuxer()
{
    if (m_packet != nullptr)
        av_packet_free(&m_packet);
    if (m_codec_context != nullptr)
        avcodec_free_context(&m_codec_context);
    if (m_format_context != nullptr)
        avformat_close_input(&m_format_context);
}

ErrorOr<NonnullOwnPtr<FFmpegDemuxer>> FFmpegDemuxer::create(NonnullOwnPtr<SeekableStream> stream)
{
    auto io_context = TRY(Media::FFmpeg::FFmpegIOContext::create(*stream));
    auto demuxer = make<FFmpegDemuxer>(move(stream), move(io_context));

    // Open the container
    demuxer->m_format_context = avformat_alloc_context();
    if (demuxer->m_format_context == nullptr)
        return Error::from_string_literal("Failed to allocate format context");
    demuxer->m_format_context->pb = demuxer->m_io_context->avio_context();
    if (avformat_open_input(&demuxer->m_format_context, nullptr, nullptr, nullptr) < 0)
        return Error::from_string_literal("Failed to open input for format parsing");

    // Read stream info; doing this is required for headerless formats like MPEG
    if (avformat_find_stream_info(demuxer->m_format_context, nullptr) < 0)
        return Error::from_string_literal("Failed to find stream info");

    demuxer->m_packet = av_packet_alloc();
    if (demuxer->m_packet == nullptr)
        return Error::from_string_literal("Failed to allocate packet");

    return demuxer;
}

static inline AK::Duration time_units_to_duration(i64 time_units, int numerator, int denominator)
{
    VERIFY(numerator != 0);
    VERIFY(denominator != 0);
    auto seconds = time_units * numerator / denominator;
    auto seconds_in_time_units = seconds * denominator / numerator;
    auto remainder_in_time_units = time_units - seconds_in_time_units;
    auto nanoseconds = ((remainder_in_time_units * 1'000'000'000 * numerator) + (denominator / 2)) / denominator;
    return AK::Duration::from_seconds(seconds) + AK::Duration::from_nanoseconds(nanoseconds);
}

static inline AK::Duration time_units_to_duration(i64 time_units, AVRational const& time_base)
{
    return time_units_to_duration(time_units, time_base.num, time_base.den);
}

DecoderErrorOr<AK::Duration> FFmpegDemuxer::total_duration()
{
    if (m_format_context->duration < 0) {
        return DecoderError::format(DecoderErrorCategory::Unknown, "Negative stream duration");
    }

    return time_units_to_duration(m_format_context->duration, 1, AV_TIME_BASE);
}

DecoderErrorOr<AK::Duration> FFmpegDemuxer::duration_of_track(Track const& track)
{
    VERIFY(track.identifier() < m_format_context->nb_streams);
    auto* stream = m_format_context->streams[track.identifier()];

    if (stream->duration >= 0) {
        return time_units_to_duration(stream->duration, stream->time_base);
    }

    // If the stream doesn't specify the duration, fallback to what the container says the duration is.
    return total_duration();
}

DecoderErrorOr<Track> FFmpegDemuxer::get_track_for_stream_index(u32 stream_index)
{
    VERIFY(stream_index < m_format_context->nb_streams);

    auto& stream = *m_format_context->streams[stream_index];
    auto type = track_type_from_ffmpeg_media_type(stream.codecpar->codec_type);
    Track track(type, stream_index);

    if (type == TrackType::Video) {
        track.set_video_data({
            .pixel_width = static_cast<u64>(stream.codecpar->width),
            .pixel_height = static_cast<u64>(stream.codecpar->height),
        });
    }

    return track;
}

DecoderErrorOr<Vector<Track>> FFmpegDemuxer::get_tracks_for_type(TrackType type)
{
    auto media_type = ffmpeg_media_type_from_track_type(type);
    Vector<Track> tracks = {};
    for (u32 i = 0; i < m_format_context->nb_streams; i++) {
        auto& stream = *m_format_context->streams[i];
        if (stream.codecpar->codec_type != media_type)
            continue;

        tracks.append(TRY(get_track_for_stream_index(i)));
    }
    return tracks;
}

DecoderErrorOr<Optional<Track>> FFmpegDemuxer::get_preferred_track_for_type(TrackType type)
{
    auto media_type = ffmpeg_media_type_from_track_type(type);
    auto best_stream_index = av_find_best_stream(m_format_context, media_type, -1, -1, nullptr, 0);
    if (best_stream_index < 0)
        return OptionalNone();

    return get_track_for_stream_index(best_stream_index);
}

DecoderErrorOr<Optional<AK::Duration>> FFmpegDemuxer::seek_to_most_recent_keyframe(Track track, AK::Duration timestamp, Optional<AK::Duration> earliest_available_sample)
{
    // FIXME: What do we do with this here?
    (void)earliest_available_sample;

    VERIFY(track.identifier() < m_format_context->nb_streams);
    auto* stream = m_format_context->streams[track.identifier()];
    auto time_base = av_q2d(stream->time_base);
    auto time_in_seconds = static_cast<double>(timestamp.to_milliseconds()) / 1000.0 / time_base;
    auto sample_timestamp = AK::round_to<int64_t>(time_in_seconds);

    if (av_seek_frame(m_format_context, stream->index, sample_timestamp, AVSEEK_FLAG_BACKWARD) < 0)
        return DecoderError::format(DecoderErrorCategory::Unknown, "Failed to seek");

    return timestamp;
}

DecoderErrorOr<CodecID> FFmpegDemuxer::get_codec_id_for_track(Track track)
{
    VERIFY(track.identifier() < m_format_context->nb_streams);
    auto* stream = m_format_context->streams[track.identifier()];
    return media_codec_id_from_ffmpeg_codec_id(stream->codecpar->codec_id);
}

DecoderErrorOr<ReadonlyBytes> FFmpegDemuxer::get_codec_initialization_data_for_track(Track track)
{
    VERIFY(track.identifier() < m_format_context->nb_streams);
    auto* stream = m_format_context->streams[track.identifier()];
    return ReadonlyBytes { stream->codecpar->extradata, static_cast<size_t>(stream->codecpar->extradata_size) };
}

DecoderErrorOr<Sample> FFmpegDemuxer::get_next_sample_for_track(Track track)
{
    VERIFY(track.identifier() < m_format_context->nb_streams);
    auto* stream = m_format_context->streams[track.identifier()];

    for (;;) {
        auto read_frame_error = av_read_frame(m_format_context, m_packet);
        if (read_frame_error < 0) {
            if (read_frame_error == AVERROR_EOF)
                return DecoderError::format(DecoderErrorCategory::EndOfStream, "End of stream");

            return DecoderError::format(DecoderErrorCategory::Unknown, "Failed to read frame");
        }
        if (m_packet->stream_index != stream->index) {
            av_packet_unref(m_packet);
            continue;
        }

        auto color_primaries = static_cast<ColorPrimaries>(stream->codecpar->color_primaries);
        auto transfer_characteristics = static_cast<TransferCharacteristics>(stream->codecpar->color_trc);
        auto matrix_coefficients = static_cast<MatrixCoefficients>(stream->codecpar->color_space);
        auto color_range = [stream] {
            switch (stream->codecpar->color_range) {
            case AVColorRange::AVCOL_RANGE_MPEG:
                return VideoFullRangeFlag::Studio;
            case AVColorRange::AVCOL_RANGE_JPEG:
                return VideoFullRangeFlag::Full;
            default:
                return VideoFullRangeFlag::Unspecified;
            }
        }();

        // Copy the packet data so that we have a permanent reference to it whilst the Sample is alive, which allows us
        // to wipe the packet afterwards.
        auto packet_data = DECODER_TRY_ALLOC(ByteBuffer::copy(m_packet->data, m_packet->size));

        auto sample = Sample(
            time_units_to_duration(m_packet->pts, stream->time_base),
            move(packet_data),
            VideoSampleData(CodingIndependentCodePoints(color_primaries, transfer_characteristics, matrix_coefficients, color_range)));

        // Wipe the packet now that the data is safe.
        av_packet_unref(m_packet);
        return sample;
    }
}

}