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• Qt Video Recorder

  11 mai 2014, par Davlog

  I am trying to create a video recorder with Qt. What I did so far was taking a screenshot of a rectangle on the screen and save it. At the end I use ffmpeg to get a video file out of the images.

  I connected a timer’s signal timeout() to my custom slot which takes the snapshot and saves it to my tmp folder. The timer has an intervall of 1000 / 30. That should be 30 times per second. But 1000 / 30 is a little bit more than 33 milliseconds so I cannot really get 30 fps. It’s a bit more.

  I recorded a youtube video with my recorder and everything was smooth but a little bit faster / slower depending on the intervall.

  So my question basically is how do I get really 30 / 40 / 50 / ... fps ?

• While transcoding to mpegts ffmpeg creates the first frame after 1.48 seconds delay

  15 mars 2018, par Biraj B Choudhury

  I have transcoded a file to mpegts using the following command

   ./ffmpeg -y -i big_buck_bunny_720p_5mb.mp4  -vcodec libx264  -x264opts "keyint=48:min-keyint=48:no_scenecut" -r 23.976 -c:a copy  -f mpegts test.mpegts

  When I run ffprobe on it -

  ./ffprobe  -i  test.mpegts  -select_streams v -show_frames -of csv

  I see that the first frame starts at 1.48 seconds why is this so ?

  Input #0, mpegts, from 'test.mpegts':
  
    Duration: 00:00:29.61, start: 1.483422, bitrate: 1964 kb/s
  
    Program 1 
  
      Metadata:
  
        service_name    : Service01
  
        service_provider: FFmpeg
  
      Stream #0:0[0x100]: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
  
      Stream #0:1[0x101](und): Audio: aac (LC) ([15][0][0][0] / 0x000F), 48000 Hz, 5.1, fltp, 406 kb/s
  
  frame,video,0,1,133508,1.483422,133508,1.483422,133508,1.483422,3753,0.041700,564,112008,1280,720,yuv420p,1:1,I,0,0,0,0,0
  
  frame,video,0,0,137262,1.525133,137262,1.525133,137262,1.525133,3753,0.041700,125584,1110,1280,720,yuv420p,1:1,B,2,0,0,0,0

  After some research I added "muxdelay 0" to my command

  ./ffmpeg -y -i big_buck_bunny_720p_5mb.mp4  -vcodec libx264  -x264opts "keyint=48:min-keyint=48:no_scenecut" -r 23.976 -c:a copy  -muxdelay 0 -f mpegts test.mpegts

  And now I get the following in ffprobe

  Input #0, mpegts, from 'test.mpegts':
  
    Duration: 00:00:29.61, start: 0.083422, bitrate: 1987 kb/s
  
    Program 1 
  
      Metadata:
  
        service_name    : Service01
  
        service_provider: FFmpeg
  
      Stream #0:0[0x100]: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
  
      Stream #0:1[0x101](und): Audio: aac (LC) ([15][0][0][0] / 0x000F), 48000 Hz, 5.1, fltp, 406 kb/s
  
  frame,video,0,1,7508,0.083422,7508,0.083422,7508,0.083422,3753,0.041700,564,112008,1280,720,yuv420p,1:1,I,0,0,0,0,0
  
  frame,video,0,0,11262,0.125133,11262,0.125133,11262,0.125133,3753,0.041700,125584,1110,1280,720,yuv420p,1:1,B,2,0,0,0,0

  Can anybody help me understand what is this muxdelay that is contributing to 1.4 seconds of delay and what is contributing to the remaining 0.08 seconds of delay.

  The first frame is at 0.000 when the output is mp4 so this is something particular to mpegts.

• Cannot find installation of real FFmpeg (which comes with ffprobe)

  29 mars 2023, par Asm Goni

  I was trying to fit a generator into a model and I got this error : 
AssertionError: Cannot find installation of real FFmpeg (which comes with ffprobe).

  



  I have looked over many of the solutions on GitHub and other questions on Stack Overflow but none of them worked for me.

  



  Here is one of the commands I ran :

  



  sudo add-apt-repository ppa:mc3man/trusty-media  
sudo apt-get update  
sudo apt-get install ffmpeg  
sudo apt-get install frei0r-plugins  


  



  pip list also indicates the presence of ffmpeg-1.4

  



  In addition, I tried force reinstalling and updating ffmpeg just in case any dependencies were not installed properly.

  



  I also set the skvideo's path for ffmpeg manually :

  



  skvideo.setFFmpegPath('/usr/local/lib/python3.6/dist-packages/ffmpeg/')


  



  This returns : /usr/local/lib/python3.6/dist-packages/skvideo/__init__.py:306: UserWarning: ffmpeg/ffprobe not found in path: /usr/local/lib/python3.6/dist-packages/ffmpeg/
  warnings.warn("ffmpeg/ffprobe not found in path: " + str(path), UserWarning)

  



  By the way, when I try installing, it also returns this error, I don't know what to do about this :

  



  Get:127 http://archive.ubuntu.com/ubuntu bionic/main amd64 vdpau-driver-all amd64 1.1.1-3ubuntu1 [4,674 B]
Fetched 60.4 MB in 7s (8,769 kB/s)
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/w/wavpack/libwavpack1_5.1.0-2ubuntu1.1_amd64.deb  404  Not Found [IP: 91.189.88.149 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?


  



  I ran apt-get update --fix-missing and that didn't make anything better.

  



  Is there a solution to this ?