qffmpegstreamdecoder.cpp

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// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#include "playbackengine/qffmpegstreamdecoder_p.h"
#include "playbackengine/qffmpegmediadataholder_p.h"
#include <qloggingcategory.h>
 
QT_BEGIN_NAMESPACE
 
static Q_LOGGING_CATEGORY(qLcStreamDecoder, "qt.multimedia.ffmpeg.streamdecoder");
 
namespace QFFmpeg {
 
StreamDecoder::StreamDecoder(const Codec &codec, qint64 absSeekPos)
    : m_codec(codec),
      m_absSeekPos(absSeekPos),
      m_trackType(MediaDataHolder::trackTypeFromMediaType(codec.context()->codec_type))
{
    qCDebug(qLcStreamDecoder) << "Create stream decoder, trackType" << m_trackType
                              << "absSeekPos:" << absSeekPos;
    Q_ASSERT(m_trackType != QPlatformMediaPlayer::NTrackTypes);
}
 
StreamDecoder::~StreamDecoder()
{
    avcodec_flush_buffers(m_codec.context());
}
 
void StreamDecoder::onFinalPacketReceived()
{
    decode({});
}
 
void StreamDecoder::decode(Packet packet)
{
    m_packets.enqueue(packet);
 
    scheduleNextStep();
}
 
void StreamDecoder::doNextStep()
{
    auto packet = m_packets.dequeue();
 
    auto decodePacket = [this](Packet packet) {
        if (trackType() == QPlatformMediaPlayer::SubtitleStream)
            decodeSubtitle(packet);
        else
            decodeMedia(packet);
    };
 
    if (packet.isValid() && packet.loopOffset().index != m_offset.index) {
        decodePacket({});
 
        qCDebug(qLcStreamDecoder) << "flush buffers due to new loop:" << packet.loopOffset().index;
 
        avcodec_flush_buffers(m_codec.context());
        m_offset = packet.loopOffset();
    }
 
    decodePacket(packet);
 
    setAtEnd(!packet.isValid());
 
    if (packet.isValid())
        emit packetProcessed(packet);
 
    scheduleNextStep(false);
}
 
QPlatformMediaPlayer::TrackType StreamDecoder::trackType() const
{
    return m_trackType;
}
 
void StreamDecoder::onFrameProcessed(Frame frame)
{
    if (frame.sourceId() != id())
        return;
 
    --m_pendingFramesCount;
    Q_ASSERT(m_pendingFramesCount >= 0);
 
    scheduleNextStep();
}
 
bool StreamDecoder::canDoNextStep() const
{
    constexpr qint32 maxPendingFramesCount = 3;
    constexpr qint32 maxPendingAudioFramesCount = 9;
 
    const auto maxCount = m_trackType == QPlatformMediaPlayer::AudioStream
            ? maxPendingAudioFramesCount
            : m_trackType == QPlatformMediaPlayer::SubtitleStream
            ? maxPendingFramesCount * 2 /*main packet and closing packet*/
            : maxPendingFramesCount;
 
    return !m_packets.empty() && m_pendingFramesCount < maxCount
            && PlaybackEngineObject::canDoNextStep();
}
 
void StreamDecoder::onFrameFound(Frame frame)
{
    if (frame.isValid() && frame.absoluteEnd() < m_absSeekPos)
        return;
 
    Q_ASSERT(m_pendingFramesCount >= 0);
    ++m_pendingFramesCount;
    emit requestHandleFrame(frame);
}
 
void StreamDecoder::decodeMedia(Packet packet)
{
    auto sendPacketResult = sendAVPacket(packet);
 
    if (sendPacketResult == AVERROR(EAGAIN)) {
        // Doc says:
        //  AVERROR(EAGAIN): input is not accepted in the current state - user
        //                   must read output with avcodec_receive_frame() (once
        //                   all output is read, the packet should be resent, and
        //                   the call will not fail with EAGAIN).
        receiveAVFrames();
        sendPacketResult = sendAVPacket(packet);
 
        if (sendPacketResult != AVERROR(EAGAIN))
            qWarning() << "Unexpected ffmpeg behavior";
    }
 
    if (sendPacketResult == 0)
        receiveAVFrames();
}
 
int StreamDecoder::sendAVPacket(Packet packet)
{
    return avcodec_send_packet(m_codec.context(), packet.isValid() ? packet.avPacket() : nullptr);
}
 
void StreamDecoder::receiveAVFrames()
{
    while (true) {
        auto avFrame = makeAVFrame();
 
        const auto receiveFrameResult = avcodec_receive_frame(m_codec.context(), avFrame.get());
 
        if (receiveFrameResult == AVERROR_EOF || receiveFrameResult == AVERROR(EAGAIN))
            break;
 
        if (receiveFrameResult < 0) {
            emit error(QMediaPlayer::FormatError, err2str(receiveFrameResult));
            break;
        }
 
        onFrameFound({ m_offset, std::move(avFrame), m_codec, 0, id() });
    }
}
 
void StreamDecoder::decodeSubtitle(Packet packet)
{
    if (!packet.isValid())
        return;
    //    qCDebug(qLcDecoder) << "    decoding subtitle" << "has delay:" <<
    //    (codec->codec->capabilities & AV_CODEC_CAP_DELAY);
    AVSubtitle subtitle;
    memset(&subtitle, 0, sizeof(subtitle));
    int gotSubtitle = 0;
 
    const int res =
            avcodec_decode_subtitle2(m_codec.context(), &subtitle, &gotSubtitle, packet.avPacket());
    //    qCDebug(qLcDecoder) << "       subtitle got:" << res << gotSubtitle << subtitle.format <<
    //    Qt::hex << (quint64)subtitle.pts;
    if (res < 0 || !gotSubtitle)
        return;
 
    // apparently the timestamps in the AVSubtitle structure are not always filled in
    // if they are missing, use the packets pts and duration values instead
    qint64 start, end;
    if (subtitle.pts == AV_NOPTS_VALUE) {
        start = m_codec.toUs(packet.avPacket()->pts);
        end = start + m_codec.toUs(packet.avPacket()->duration);
    } else {
        auto pts = timeStampUs(subtitle.pts, AVRational{ 1, AV_TIME_BASE });
        start = *pts + qint64(subtitle.start_display_time) * 1000;
        end = *pts + qint64(subtitle.end_display_time) * 1000;
    }
 
    if (end <= start) {
        qWarning() << "Invalid subtitle time";
        return;
    }
    //        qCDebug(qLcDecoder) << "    got subtitle (" << start << "--" << end << "):";
    QString text;
    for (uint i = 0; i < subtitle.num_rects; ++i) {
        const auto *r = subtitle.rects[i];
        //            qCDebug(qLcDecoder) << "    subtitletext:" << r->text << "/" << r->ass;
        if (i)
            text += QLatin1Char('\n');
        if (r->text)
            text += QString::fromUtf8(r->text);
        else {
            const char *ass = r->ass;
            int nCommas = 0;
            while (*ass) {
                if (nCommas == 8)
                    break;
                if (*ass == ',')
                    ++nCommas;
                ++ass;
            }
            text += QString::fromUtf8(ass);
        }
    }
    text.replace(QLatin1String("\\N"), QLatin1String("\n"));
    text.replace(QLatin1String("\\n"), QLatin1String("\n"));
    text.replace(QLatin1String("\r\n"), QLatin1String("\n"));
    if (text.endsWith(QLatin1Char('\n')))
        text.chop(1);
 
    onFrameFound({ m_offset, text, start, end - start, id() });
 
    // TODO: maybe optimize
    onFrameFound({ m_offset, QString(), end, 0, id() });
}
} // namespace QFFmpeg
 
QT_END_NAMESPACE
 
#include "moc_qffmpegstreamdecoder_p.cpp"