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• ffmpeg audio - video sync issue (audio ahead of video) - while screen recording using x11grab

  12 juillet 2023, par maheshg

  While screen-recording using the below ffmpeg options I consistently get audio ahead of video, delay is in the order of few seconds

  


  ffmpeg cmd :

  


  ffmpeg -y -f x11grab -thread_queue_size 1024 -draw_mouse 0 -video_size 1920x1080 -i :0 -f pulse -thread_queue_size 1024 -i default -c:v libx264 -threads 0 -preset faster -c:a flac -async 1 -vsync 1 -crf 30 -crf_max 33 -f matroska output.mkv

  


  ffprobe output below :

  


  $ ffprobe demo.mkv 
ffprobe version 3.4.4-1~16.04.york0 Copyright (c) 2007-2018 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.10) 20160609
  configuration: --prefix=/usr --extra-version='1~16.04.york0' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libavresample   3.  7.  0 /  3.  7.  0
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
Input #0, matroska,webm, from 'demo.mkv':
  Metadata:
    ENCODER         : Lavf57.71.100
  Duration: 01:00:31.93, start: 0.000000, bitrate: 416 kb/s
    Stream #0:0: Video: h264 (High), yuv420p(progressive), 1920x1080, 29.97 fps, 29.97 tbr, 1k tbn, 59.94 tbc (default)
    Metadata:
      ENCODER         : Lavc57.89.100 libx264
      DURATION        : 01:00:31.928000000
    Stream #0:1: Audio: flac, 48000 Hz, stereo, s16 (default)
    Metadata:
      ENCODER         : Lavc57.89.100 flac
      DURATION        : 01:00:30.912000000


  


  I have even tried using avoid_negative_ts flag, but it didnt help with the sync issue.

  


  


  OS : Ubuntu-18.04

  


  ffmpeg version : 3.4

  


  


  Update : (with ffmpeg-4.0)
I have since split this process into 2 parts and tried as shown below (quality is better, but audio/video sync is still an issue)

  


  # STEP-1: screen recording
/usr/bin/ffmpeg -y -f x11grab -thread_queue_size 1024 -draw_mouse 0 \
-video_size 1920x1080 -i :91141925 -f pulse -thread_queue_size 1024 \
-i virtual_sink.monitor -c:v libx264rgb -threads 0 -preset ultrafast \
-c:a flac -ac 1 -crf 0 -f matroska output.mkv

# STEP-2: audio/video encoding
/usr/bin/ffmpeg -y -i output.mkv -c:v libx264 -threads 0 \
-preset faster -pix_fmt yuv420p -c:a copy -ac 1 -crf 25 \
-f matroska final_output.mkv


  


  STEP-1 uses much less CPU during screen recording, but audio is still ahead of video. the display I am using is xvfb one in STEP-1 (since, this is a headless machine in the cloud)

  


  Also, i have tried flags -filter_complex aresample=44100 -vsync 1 in STEP-1 to no avail.

  


  Can someone please help !

  


  


  Update 2 : (with latest ffmpeg from git master)

  


  IT WORKED ! THANKS @llogan for the helpful comments.

  


  


• Ffmpeg - how to ?

  24 novembre 2017, par Jamie Vardy

  I am working on an android app that allows a user to post videos files to an online server I suceeded in doing that but the problem come when uploading large videos. I am thinking of compressing the video before upload and I heard about ffmpeg but the thing is that I am just a beginner and I don’t know where to start. Please what step do I need to follow to start using ffmpeg on android studio and how to use it to compress android videos

• Debugging FFmpeg

  12 juillet 2016, par NadavRub

  I am using FFmpeg @ Android and would like to be able to step-in to the FFmpeg code ( Eclipse + Seqouya ), while compiling FFmpeg I use the --disable-stripping --enable-debug=3 flags, still, stepping in with the debugger throws me at some unrelated line of code.

  What settings should I use to enable FFmpeg debugging ?