qffmpegcodeccontext.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/qffmpegcodeccontext_p.h"
#include "qffmpegcodecstorage_p.h"
 
#include <QtMultimedia/qplaybackoptions.h>
#include <QtCore/qloggingcategory.h>
 
QT_BEGIN_NAMESPACE
 
using namespace Qt::StringLiterals;
 
Q_STATIC_LOGGING_CATEGORY(qLcPlaybackEngineCodec, "qt.multimedia.playbackengine.codec");
 
namespace QFFmpeg {
 
CodecContext::Data::Data(AVCodecContextUPtr context, AVStream *avStream,
                         AVFormatContext *avFormatContext,
                         std::unique_ptr<QFFmpeg::HWAccel> hwAccel)
    : context(std::move(context)),
      stream(avStream),
      formatContext(avFormatContext),
      hwAccel(std::move(hwAccel))
{
    if (stream->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
        pixelAspectRatio = av_guess_sample_aspect_ratio(formatContext, stream, nullptr);
}
 
q23::expected<CodecContext, QString> CodecContext::create(AVStream *stream,
                                                          AVFormatContext *formatContext,
                                                          const QPlaybackOptions &options)
{
    if (!stream)
        return q23::unexpected{ u"Invalid stream"_s };
 
    if (stream->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
        auto hwCodec = create(stream, formatContext, options, Hw);
        if (hwCodec)
            return hwCodec;
 
        qCInfo(qLcPlaybackEngineCodec) << hwCodec.error();
    }
 
    auto context = create(stream, formatContext, options, Sw);
    if (!context)
        qCWarning(qLcPlaybackEngineCodec) << context.error();
 
    return context;
}
 
AVRational CodecContext::pixelAspectRatio(AVFrame *frame) const
{
    // does the same as av_guess_sample_aspect_ratio, but more efficient
    return d->pixelAspectRatio.num && d->pixelAspectRatio.den ? d->pixelAspectRatio
                                                              : frame->sample_aspect_ratio;
}
 
q23::expected<CodecContext, QString> CodecContext::create(AVStream *stream,
                                                          AVFormatContext *formatContext,
                                                          const QPlaybackOptions &options,
                                                          VideoCodecCreationPolicy videoCodecPolicy)
{
    Q_ASSERT(stream);
 
    if (videoCodecPolicy == Hw && stream->codecpar->codec_type != AVMEDIA_TYPE_VIDEO)
        Q_ASSERT(!"Codec::create has been called with Hw policy on a non-video stream");
 
    std::optional<Codec> decoder;
    std::unique_ptr<QFFmpeg::HWAccel> hwAccel;
 
    if (videoCodecPolicy == Hw)
        std::tie(decoder, hwAccel) = HWAccel::findDecoderWithHwAccel(stream->codecpar->codec_id);
    else
        decoder = QFFmpeg::findAVDecoder(stream->codecpar->codec_id);
 
    if (!decoder)
        return q23::unexpected{ u"No %1 decoder found"_s.arg(videoCodecPolicy == Hw ? "HW"
                                                                                    : "SW") };
 
    qCDebug(qLcPlaybackEngineCodec)
            << "found decoder" << decoder->name() << "for id" << decoder->id();
 
    AVCodecContextUPtr context(avcodec_alloc_context3(decoder->get()));
    if (!context)
        return q23::unexpected{ u"Failed to allocate a FFmpeg codec context"_s };
 
    // Use HW decoding even if the codec level doesn't match the reported capabilities
    // of the hardware. FFmpeg documentation recommendeds setting this flag by default.
    context->hwaccel_flags |= AV_HWACCEL_FLAG_IGNORE_LEVEL;
 
    static const bool allowProfileMismatch = static_cast<bool>(
            qEnvironmentVariableIntValue("QT_FFMPEG_HW_ALLOW_PROFILE_MISMATCH"));
    if (allowProfileMismatch) {
        // Use HW decoding even if the codec profile doesn't match the reported capabilities
        // of the hardware.
        context->hwaccel_flags |= AV_HWACCEL_FLAG_ALLOW_PROFILE_MISMATCH;
    }
 
    if (hwAccel)
        context->hw_device_ctx = av_buffer_ref(hwAccel->hwDeviceContextAsBuffer());
 
    if (context->codec_type != AVMEDIA_TYPE_AUDIO && context->codec_type != AVMEDIA_TYPE_VIDEO
        && context->codec_type != AVMEDIA_TYPE_SUBTITLE) {
        return q23::unexpected{ u"Unknown codec type"_s };
    }
 
    int ret = avcodec_parameters_to_context(context.get(), stream->codecpar);
    if (ret < 0)
        return q23::unexpected{
            QStringLiteral("Failed to set FFmpeg codec parameters: %1").arg(err2str(ret))
        };
 
    // Required so that decoders can rescale packet-side timestamps (e.g. when
    // trimming AAC/Opus priming/padding samples signalled via skip_samples).
    context->pkt_timebase = stream->time_base;
 
    // ### This still gives errors about wrong HW formats (as we accept all of them)
    // But it would be good to get so we can filter out pixel format we don't support natively
    context->get_format = QFFmpeg::getFormat;
 
    /* Init the decoder, with reference counting and threading */
    AVDictionaryHolder opts;
    if (options.playbackIntent() == QPlaybackOptions::PlaybackIntent::LowLatencyStreaming)
        av_dict_set(opts, "flags", "low_delay", 0);
 
    av_dict_set(opts, "refcounted_frames", "1", 0);
    av_dict_set(opts, "threads", "auto", 0);
    applyExperimentalCodecOptions(*decoder, opts);
 
    ret = avcodec_open2(context.get(), decoder->get(), opts);
 
    if (ret < 0)
        return q23::unexpected{
            QStringLiteral("Failed to open FFmpeg codec context: %1").arg(err2str(ret))
        };
 
    return CodecContext(new Data(std::move(context), stream, formatContext, std::move(hwAccel)));
}
 
QT_END_NAMESPACE
 
} // namespace QFFmpeg