PTS and DTS calculation for video and audio frames

问题

I am receiving video H264 encoded data and audio G.711 PCM encoded data from two different threads to mux / write into mov multimedia container.

The writer function signatures are like:

bool WriteAudio(const unsigned char *pEncodedData, size_t iLength);
bool WriteVideo(const unsigned char *pEncodedData, size_t iLength, bool const bIFrame);

And the function for adding audio and video streams looks like:

AVStream* AudioVideoRecorder::AddMediaStream(enum AVCodecID codecID) {
    Log("Adding stream: %s.", avcodec_get_name(codecID));
    AVCodecContext* pCodecCtx;
    AVStream* pStream;

    /* find the encoder */
    AVCodec* codec = avcodec_find_encoder(codecID);
    if (!codec) {
        LogErr("Could not find encoder for %s", avcodec_get_name(codecID));
        return NULL;
    }

    pStream = avformat_new_stream(m_pFormatCtx, codec);
    if (!pStream) {
        LogErr("Could not allocate stream.");
        return NULL;
    }
    pStream->id = m_pFormatCtx->nb_streams - 1;
    pStream->time_base = (AVRational){1, VIDEO_FRAME_RATE};
    pCodecCtx = pStream->codec;


    switch(codec->type) {
    case AVMEDIA_TYPE_VIDEO:
        pCodecCtx->codec_id = codecID;
        pCodecCtx->bit_rate = VIDEO_BIT_RATE;
        pCodecCtx->width = PICTURE_WIDTH;
        pCodecCtx->height = PICTURE_HEIGHT;
        pCodecCtx->gop_size = VIDEO_FRAME_RATE;
        pCodecCtx->pix_fmt = PIX_FMT_YUV420P;
        m_pVideoStream = pStream;
        break;

    case AVMEDIA_TYPE_AUDIO:
        pCodecCtx->codec_id = codecID;
        pCodecCtx->sample_fmt = AV_SAMPLE_FMT_S16;
        pCodecCtx->bit_rate = 64000;
        pCodecCtx->sample_rate = 8000;
        pCodecCtx->channels = 1;
        m_pAudioStream = pStream;
        break;

    default:
        break;
    }

    /* Some formats want stream headers to be separate. */
    if (m_pOutputFmt->flags & AVFMT_GLOBALHEADER)
        m_pFormatCtx->flags |= CODEC_FLAG_GLOBAL_HEADER;

    return pStream;
}

Inside WriteAudio(..) and WriteVideo(..) functions, I am creating AVPakcet using av_init_packet(...) and set pEncodedData and iLength as packet.data and packet.size. I printed packet.pts and packet.dts and its equivalent to AV_NOPTS_VALUE.

Now, how do I calculate the PTS, DTS, and packet duration (packet.dts, packet.pts and packet.duration) correctly for both audio and video data so that I can sync audio & video and play it properly? I saw many examples on the internet, but none of them are making sense to me. I am new with ffmpeg, and my conception may not be correct in some context. I want to do it in the appropriate way.

Thanks in advance!

EDIT: In my video streams, there is no B frame. So, I think PTS and DTS can be kept the same here.

回答1:

PTS/DTS are timestamps, they should be set to the timestamps of the input data. I don't know where your date comes from, but any input has some form of timestamps associated with it. Typically, the timestamps of the input media file or a system clock-derived metric if you're recording from your soundcard+webcam, and so on. You should convert these numbers into the form expected, and then assign them to AVPacket.pts/dts.

来源：https://stackoverflow.com/questions/31917032/pts-and-dts-calculation-for-video-and-audio-frames

标签

c++

audio

video

ffmpeg

mux