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• FFMPEG : audio unsynchronized, losing framerate and strange behavior when pavucontrol is open

  10 mars 2021, par Rik Ferreira

  I'm trying to record my desktop screen with internal audio and mic, but I'm noticing some issues with the output, according to this empirical scale :

  


  

  • If I record only the desktop, the output is GOOD.

  


  • If I record the desktop + mic, the output is GOOD.

  


  • If I record the desktop + internal audio only, the output is BAD.

  


  • If I record the desktop + mic + internal audio, the output is BAD.

  


  • If I record the desktop + mic + internal audio + open pavucontrol, the output is GOOD.

  


  


  Good means the two audio sources and the video are acceptably synchronized and bad means not synchronized at all.

  


  I recorded some samples to show what is going on :

  


  

  • Screen + Mic + Internal audio

  


  • Screen + Mic

  


  • Screen + Mic + Internal audio + pavucontrol

  


  


  I'm snapping my fingers near the microphone when the Beep! message appears along with the sound.

  


  I'm using a simple script to play a sound and show a message in the terminal instead of using pavucontrol because it masks the problem.

  


  FFMPEG call

  


  Although the entire script is visible in the videos, here is the ffmpeg call in plain text :

  


  Dual audio

  


  ffmpeg -y \
    -f x11grab -s 1920x1080 -i :0.0 \
    -f pulse -i 0 \
    -f pulse -i 1 \
    -filter_complex amix=inputs=2 \
    output.mp4


  


  Only microphone

  


  ffmpeg -y \
    -f x11grab -s 1920x1080 -i :0.0 \
    -f pulse -i 1 \
    output.mp4


  


  Other info

  


  SO : Arch Linux

  


  When pavucontrol isn't open, pacmd list-source-outputs returns : 0 source output(s) available., but when pavucontrol is open :

  


  pacmd list-source-outputs | grep source

2 source output(s) available.
        source: 0 
                module-stream-restore.id = "source-output-by-application-id:org.PulseAudio.pavucontrol"
        source: 1 
                module-stream-restore.id = "source-output-by-application-id:org.PulseAudio.pavucontrol"


  


  What am I missing ? Why the ffmpeg works fine when pavucontrol is open ?

  


• OpenCV : Cannot open camera with CAP_FFMPEG even though ffmpeg is installed

  24 février 2021, par cildiracagim

  Initializing a camera video capture using CAP_FFMPEG fails even though I have ffmpeg installed :

  


  cv::VideoCapture vcap;
vcap.open(0, cv::CAP_FFMPEG);

// After these, vcap.isOpened() returns false.


  


  However, it works perfectly when I open a file in the same way :

  


  cv::VideoCapture vcap;
vcap.open(argv[1], cv::CAP_FFMPEG);

/* Correctly opens the video file at path argv[1],
vcap.isOpened() returns true. */


  


  The problem occurs in both OpenCV versions installed in my system : 4.5.1 and 3.2.0. Version 3.2.0 came installed in my Linux distribution but I have compiled 4.5.1 myself. During compilation, I have verified that CMake succesfully recognized the ffmpeg installation in my system. I guess the problem is not related to OpenCV not recognizing ffmpeg since I can open and work on video files without any problems on both OpenCV versions.

  


  Any help is greatly appreciated.

  


• ffmpeg : error while loading shared libraries : libmp3lame.so.0 : cannot open shared object file : No such file or directory

  17 février 2021, par GetItDone

  I am using this buildpack (heroku-python-buildpack-ffmpeg-lame) for my app on heroku that uses ffmpeg to convert uploaded videos to .mp4. I had been using the version without libmp3lame, and since I switched I am getting the error

  



  ffmpeg: error while loading shared libraries: libmp3lame.so.0: cannot open shared object file: No such file or directory


  



  I checked to see where libmp3lame.so.0 is located on my server with heroku run —app myapp find / -name libmp3lame.so.0, and the resulting path was /app/vendor/lame/lib/libmp3lame.so.0. I tried adding /vendor/lame/lib to my heroku path using the heroku config:set command, but even after adding it I still get the same error. Anyone know what the problem could be ?