LOG_INFO("Compute the video bitrate by decoding the first GOP.")

if(!_codecContext->width || !_codecContext->height)

throw std::runtime_error("cannot compute bit rate: invalid frame size");

if(!_formatContext || !_codec)

throw std::runtime_error("cannot compute bit rate: unknown format or codec");

if(!_codecContext->width || !_codecContext->height)

throw std::runtime_error("cannot compute bit rate: invalid frame size");

// discard no frame type when decode

_codecContext->skip_frame = AVDISCARD_NONE;

Frame frame;

AVPacket pkt;

av_init_packet(&pkt);

avcodec_open2(_codecContext, _codec, NULL);

int gotFrame = 0;

size_t nbDecodedFrames = 0;

int gopFramesSize = 0;

int positionOfFirstKeyFrame = -1;

int positionOfLastKeyFrame = -1;

while(!av_read_frame(const_cast<AVFormatContext*>(_formatContext), &pkt))

{

if(pkt.stream_index == (int)_streamIndex)

{

avcodec_decode_video2(_codecContext, &frame.getAVFrame(), &gotFrame, &pkt);

if(gotFrame)

{

// check distance between key frames

AVFrame& avFrame = frame.getAVFrame();

if(avFrame.pict_type == AV_PICTURE_TYPE_I)

{

if(positionOfFirstKeyFrame == -1)

positionOfFirstKeyFrame = nbDecodedFrames;

else

positionOfLastKeyFrame = nbDecodedFrames;

}

++nbDecodedFrames;

// added size of all frames of the same gop

if(positionOfLastKeyFrame == -1)

{

#if LIBAVUTIL_VERSION_INT >= AV_VERSION_INT(54, 7, 100)

gopFramesSize += frame.getEncodedSize();

#else

gopFramesSize += pkt.size;

#endif

}

}

}

av_free_packet(&pkt);

if(positionOfFirstKeyFrame != -1 && positionOfLastKeyFrame != -1)

break;

}

// Close a given AVCodecContext and free all the data associated with it (but not the AVCodecContext itself)

avcodec_close(_codecContext);

// Returns at the beginning of the stream

const_cast<FormatContext*>(&_fileProperties->getFormatContext())->seek(0, AVSEEK_FLAG_BYTE);

const size_t gopSize = positionOfLastKeyFrame - positionOfFirstKeyFrame;

if(gopSize > 0)

const float fps = av_q2d(_formatContext->streams[_streamIndex]->avg_frame_rate);

return (gopFramesSize / gopSize) * 8 * fps;

return 0;