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• FFMPEG C++ API audio/video sync, video is longer [closed]

  11 mai 2023, par Gábor Gombor

  I create a video from frames in C++ with a given FPS and supply it to FFMPEG API. I record from an Unreal engine viewport and feed FFMPEG with the images. In this interval I have also an audio track in FLAC which I want sync with the video. When the music ends, I close the video and merge them, but the final video has sync problems, the video is a little bit longer than the audio, so I will have an increasing delay. For example I record 0:55 secs, the audio is ok=same length, but the video from frames will be 0:56 secs.

  


  I think the following code is problematic :

  


  bool MyVideoExporter::writeFrame(OutputStream* oStream, AVFrame* frame, int& framePTS)
{
    auto* packet = oStream->pkt->pkt;
    auto* codecContext = oStream->enc->codecContext;

    frame->pts = framePTS;
    frame->pkt_dts = frame->pts;

    auto ret = avcodec_send_frame(codecContext, frame);
    if (ret >= 0) {
        auto retVal = 0;
        while (retVal >= 0) {
            retVal = avcodec_receive_packet(codecContext, packet);
            if (retVal == AVERROR(EAGAIN) || retVal == AVERROR_EOF) break;
            else if (retVal < 0) {
                return false;
            }

            // rescale to audio, usually 1/44100
            av_packet_rescale_ts(packet, m_audiotimestamp, oStream->st->time_base);
            // rescale to FPS, usually 1/30 or 1/60
            av_packet_rescale_ts(packet, codecContext->time_base, oStream->st->time_base);

            packet->stream_index = oStream->st->index;

            retVal = av_interleaved_write_frame(m_avFormatContext.avFormatContext, packet);
            if (retVal < 0) {
                return false;
            }

            framePTS++;
        }

        return retVal == AVERROR_EOF;
    }

    return false;
}



  


  Any idea what is wrong ?

  


  I tried change the order of av_packet_rescale_ts lines or move the frame increase code to another places, but getting far worse results.

  


• RMPT Stream Startup Dalay on FFMPEG and Gstreamer compared to OBS

  24 mars 2023, par Arruda

  I'm trying to use ffmpeg to stream a video into my RTMP server.
The problem I'm having right now is that FFMPEG seems to take a long time to start streaming the output (from what I see in my Oven Media Engine server).

  


  At the same time, when I use OBS Studio my stream starts almost immediately.
I also tried using Gstreamer, and got the same amount of delay when using FFMPEG.

  


  After a long process, I finally saw that if I added an empty audio track, then FFMPEG would start as quickly as OBS.

  


  This is my final FFMPEG command (using the empty audio track) :

  


  ffmpeg -f v4l2 -i /dev/video0 -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=44100 -profile:v main -pix_fmt yuv420p -preset ultrafast -tune zerolatency -vcodec libx264 -r 10 -g 10 -keyint_min 10 -sc_threshold 0 -b:v 2000k -maxrate 2000k -bufsize 2000k -s 768x432 -acodec aac  -f flv rtmp://localhost:1935/app/mystream


  


  I'm streaming my webcam at 768x432, at 10FPS.

  


  Now, is this a bad solution in the case where there is no need for an audio in the output video ?

  


  There is no problem, nor noticible delay in the videstream if I remove the audio, the only downside is the startup time that is about 30-40 seconds.

  


  Is this delay when not using a audio track a FFMPEG issue ? or is this related to how the Oven Media Engine ingest the RTMP stream ?

  


• Need to install ffmpeg (non static) for my discord bot (node.js) hosted on Heroku

  23 mars 2023, par febkosq8

  I host my Discord Bot on Heroku.

  


  I was using the static ffmpeg buildpack by jonathanong until now.

  


  Due to some issues with Discord-Player package that I use to play music, I will have to use non static version of ffmpeg (See Issue #1639 for more info).

  


  I tried using the aptFile buildpack to install ffmpeg directly.
The build process takes place without any issues. See build log (Pastebin Logs).

  


  But after deploy, I am not able to access ffmpeg.

  


  I keep getting
ffmpeg: error while loading shared libraries: libusb-1.0.so.0: cannot open shared object file: No such file or directory when i try to run ffmpeg thro heroku run command. The bot is also not able to pickup ffmpeg.

  


  ffmpeg fails to run

  


  I am using heroku stack-20 because it was a workaround to the github issue mentioned earlier. The issue exists in stack-22 also.

  


  Need help to figure out a solution for this problem or a way to install non static versions of ffmpeg