ladybird/Libraries/LibMedia/FFmpeg/FFmpegAudioDecoder.cpp

/*
 * Copyright (c) 2025, Gregory Bertilson <gregory@ladybird.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibCore/System.h>
#include <LibMedia/AudioBlock.h>
#include <LibMedia/FFmpeg/FFmpegHelpers.h>

#include "FFmpegAudioDecoder.h"

namespace Media::FFmpeg {

DecoderErrorOr<NonnullOwnPtr<FFmpegAudioDecoder>> FFmpegAudioDecoder::try_create(CodecID codec_id, ReadonlyBytes codec_initialization_data)
{
    AVCodecContext* codec_context = nullptr;
    AVPacket* packet = nullptr;
    AVFrame* frame = nullptr;
    ArmedScopeGuard memory_guard {
        [&] {
            avcodec_free_context(&codec_context);
            av_packet_free(&packet);
            av_frame_free(&frame);
        }
    };

    auto ff_codec_id = ffmpeg_codec_id_from_media_codec_id(codec_id);
    auto const* codec = avcodec_find_decoder(ff_codec_id);
    if (!codec)
        return DecoderError::format(DecoderErrorCategory::NotImplemented, "Could not find FFmpeg decoder for codec {}", codec_id);

    codec_context = avcodec_alloc_context3(codec);
    if (!codec_context)
        return DecoderError::format(DecoderErrorCategory::Memory, "Failed to allocate FFmpeg codec context for codec {}", codec_id);

    codec_context->time_base = { 1, 1'000'000 };
    codec_context->thread_count = static_cast<int>(min(Core::System::hardware_concurrency(), 4));

    if (!codec_initialization_data.is_empty()) {
        if (codec_initialization_data.size() > NumericLimits<int>::max())
            return DecoderError::corrupted("Codec initialization data is too large"sv);

        codec_context->extradata = static_cast<u8*>(av_malloc(codec_initialization_data.size() + AV_INPUT_BUFFER_PADDING_SIZE));
        if (!codec_context->extradata)
            return DecoderError::with_description(DecoderErrorCategory::Memory, "Failed to allocate codec initialization data buffer for FFmpeg codec"sv);

        memcpy(codec_context->extradata, codec_initialization_data.data(), codec_initialization_data.size());
        codec_context->extradata_size = static_cast<int>(codec_initialization_data.size());
    }

    if (avcodec_open2(codec_context, codec, nullptr) < 0)
        return DecoderError::format(DecoderErrorCategory::Unknown, "Unknown error occurred when opening FFmpeg codec {}", codec_id);

    packet = av_packet_alloc();
    if (!packet)
        return DecoderError::with_description(DecoderErrorCategory::Memory, "Failed to allocate FFmpeg packet"sv);

    frame = av_frame_alloc();
    if (!frame)
        return DecoderError::with_description(DecoderErrorCategory::Memory, "Failed to allocate FFmpeg frame"sv);

    memory_guard.disarm();
    return DECODER_TRY_ALLOC(try_make<FFmpegAudioDecoder>(codec_context, packet, frame));
}

FFmpegAudioDecoder::FFmpegAudioDecoder(AVCodecContext* codec_context, AVPacket* packet, AVFrame* frame)
    : m_codec_context(codec_context)
    , m_packet(packet)
    , m_frame(frame)
{
}

FFmpegAudioDecoder::~FFmpegAudioDecoder()
{
    av_packet_free(&m_packet);
    av_frame_free(&m_frame);
    avcodec_free_context(&m_codec_context);
}

DecoderErrorOr<void> FFmpegAudioDecoder::receive_coded_data(AK::Duration timestamp, ReadonlyBytes coded_data)
{
    VERIFY(coded_data.size() < NumericLimits<int>::max());

    m_packet->data = const_cast<u8*>(coded_data.data());
    m_packet->size = static_cast<int>(coded_data.size());
    m_packet->pts = timestamp.to_microseconds();
    m_packet->dts = m_packet->pts;

    auto result = avcodec_send_packet(m_codec_context, m_packet);
    switch (result) {
    case 0:
        return {};
    case AVERROR(EAGAIN):
        return DecoderError::with_description(DecoderErrorCategory::NeedsMoreInput, "FFmpeg decoder cannot decode any more data until frames have been retrieved"sv);
    case AVERROR_EOF:
        return DecoderError::with_description(DecoderErrorCategory::EndOfStream, "FFmpeg decoder has been flushed"sv);
    case AVERROR(EINVAL):
        return DecoderError::with_description(DecoderErrorCategory::Invalid, "FFmpeg codec has not been opened"sv);
    case AVERROR(ENOMEM):
        return DecoderError::with_description(DecoderErrorCategory::Memory, "FFmpeg codec ran out of internal memory"sv);
    default:
        return DecoderError::with_description(DecoderErrorCategory::Corrupted, "FFmpeg codec reports that the data is corrupted"sv);
    }
}

template<typename T>
static float float_sample_from_frame_data(u8** data, size_t plane, size_t index);

template<>
float float_sample_from_frame_data<u8>(u8** data, size_t plane, size_t index)
{
    return static_cast<float>(data[plane][index] - 127) / 255;
}

template<typename T>
requires(IsSigned<T>)
static float float_sample_from_frame_data(u8** data, size_t plane, size_t index)
{
    auto* pointer = reinterpret_cast<T*>(data[plane]);
    return pointer[index] / static_cast<float>(NumericLimits<T>::max());
}

template<typename T>
requires(IsFloatingPoint<T>)
static float float_sample_from_frame_data(u8** data, size_t plane, size_t index)
{
    auto* pointer = reinterpret_cast<T*>(data[plane]);
    return pointer[index];
}

DecoderErrorOr<void> FFmpegAudioDecoder::write_next_block(AudioBlock& block)
{
    auto result = avcodec_receive_frame(m_codec_context, m_frame);

    switch (result) {
    case 0: {
        auto timestamp = AK::Duration::from_microseconds(m_frame->pts);

        if (m_frame->ch_layout.nb_channels > 2)
            return DecoderError::not_implemented();

        VERIFY(m_frame->sample_rate > 0);
        VERIFY(m_frame->ch_layout.nb_channels > 0);

        block.emplace(m_frame->sample_rate, m_frame->ch_layout.nb_channels, timestamp, [&](AudioBlock::Data& data) {
            auto format = static_cast<AVSampleFormat>(m_frame->format);
            auto is_planar = av_sample_fmt_is_planar(format) != 0;
            auto planar_format = av_get_planar_sample_fmt(format);

            VERIFY(m_frame->nb_samples >= 0);
            auto sample_count = static_cast<size_t>(m_frame->nb_samples);
            auto channel_count = static_cast<size_t>(m_frame->ch_layout.nb_channels);
            auto count = sample_count * channel_count;
            data = MUST(AudioBlock::Data::create(count));

            auto sample_size = [&] {
                switch (planar_format) {
                case AV_SAMPLE_FMT_U8P:
                    return sizeof(u8);
                case AV_SAMPLE_FMT_S16P:
                    return sizeof(i16);
                case AV_SAMPLE_FMT_S32P:
                    return sizeof(i32);
                case AV_SAMPLE_FMT_FLTP:
                    return sizeof(float);
                case AV_SAMPLE_FMT_DBLP:
                    return sizeof(double);
                case AV_SAMPLE_FMT_S64P:
                    return sizeof(i64);
                default:
                    VERIFY_NOT_REACHED();
                }
            }();

            VERIFY(m_frame->linesize[0] > 0);
            if (is_planar)
                VERIFY(static_cast<size_t>(m_frame->linesize[0]) >= sample_count * sample_size);
            else
                VERIFY(static_cast<size_t>(m_frame->linesize[0]) >= sample_count * channel_count * sample_size);

            for (size_t i = 0; i < count; i++) {
                size_t plane = 0;
                size_t index_in_plane = i;
                if (is_planar) {
                    plane = i % channel_count;
                    index_in_plane = i / channel_count;
                }

                auto float_sample = [&] {
                    switch (planar_format) {
                    case AV_SAMPLE_FMT_U8P:
                        return float_sample_from_frame_data<u8>(m_frame->extended_data, plane, index_in_plane);
                    case AV_SAMPLE_FMT_S16P:
                        return float_sample_from_frame_data<i16>(m_frame->extended_data, plane, index_in_plane);
                    case AV_SAMPLE_FMT_S32P:
                        return float_sample_from_frame_data<i32>(m_frame->extended_data, plane, index_in_plane);
                    case AV_SAMPLE_FMT_FLTP:
                        return float_sample_from_frame_data<float>(m_frame->extended_data, plane, index_in_plane);
                    case AV_SAMPLE_FMT_DBLP:
                        return float_sample_from_frame_data<double>(m_frame->extended_data, plane, index_in_plane);
                    case AV_SAMPLE_FMT_S64P:
                        return float_sample_from_frame_data<i64>(m_frame->extended_data, plane, index_in_plane);
                    default:
                        VERIFY_NOT_REACHED();
                    }
                }();
                data[i] = float_sample;
            }
        });

        return {};
    }
    case AVERROR(EAGAIN):
        return DecoderError::with_description(DecoderErrorCategory::NeedsMoreInput, "FFmpeg decoder has no frames available, send more input"sv);
    case AVERROR_EOF:
        return DecoderError::with_description(DecoderErrorCategory::EndOfStream, "FFmpeg decoder has been flushed"sv);
    case AVERROR(EINVAL):
        return DecoderError::with_description(DecoderErrorCategory::Invalid, "FFmpeg codec has not been opened"sv);
    default:
        return DecoderError::format(DecoderErrorCategory::Unknown, "FFmpeg codec encountered an unexpected error retrieving frames with code {:x}", result);
    }
}

void FFmpegAudioDecoder::flush()
{
    avcodec_flush_buffers(m_codec_context);
}

}