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• Changing video encoding quality : Raspberry pi+v4l2 (ffmpeg or direct v4l2 API)

  24 octobre 2023, par Bill Shubert

  We are using a raspberry pi 4 to acquire video. Using the x264 library for software encoding, we were able to select a usable quality level (generally in the 16-20 range), but the compression speed was much too slow to keep up with the video feed. We switched to ffmpeg's v4l2 hardware encoder, and it's plenty fast enough to keep up with the incoming video, but now the output is poor quality, too low to be usable for our application. We have tried the ffmpeg -crf flag from 20 all the way down to 5, and it seems to have little or no effect on the video quality. I dug through the ffmpeg source code and can't find any references to "crf", "quality", or even compression rate in the v4l2 codec of ffmpeg.

  


  Is there a way to change the quality level of your encoded video using the PI's v4l2 hardware video encoder ? If so, does ffmpeg support it in some way ? Hopefully I just missed how to pass it in. If raspi+video4linux does support selecting output quality, but ffmpeg doesn't use it, then I could either patch ffmpeg or write my own code to drive v4l2, but it's not a simple API to use so I'd rather stay with ffmpeg if I can.

  


• Merge video files having audio using ffmpeg

  25 mai 2015, par Utkarsh Srivastav

  So here is my problem.
  I have 2 video files :

  • a.mp4 (2 seconds)
  • b.mp4 (4 seconds).

  I have 2 audio files :

  • c.mp3 (6 seconds)
  • d.mp3 (4 seconds).

  I created a file x.mp4 by merging a.mp4 and c.mp3 by following command

  ffmpeg  -i a.mp4 -i c.mp3 -c:v copy -c:a aac -strict experimental -map 0:v:0 -map 1:a:0 x.mp4

  The resulting file x.mp4 is of length 6 seconds in which I see first 2 seconds of video and 6 seconds of audio.

  Similarly I merged b.mp4 and d.mp3 to create y.mp4 which is of 4 seconds in which both audio and video are of 4 seconds.

  I now want to merge x.mp4 and y.mp4 to create z.mp4. I follow these commands.

  ffmpeg -i x.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts p.ts
  
  
  
  ffmpeg -i y.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts q.ts
  
  
  
  ffmpeg-0 -i "concat:p.ts|q.ts" -c copy -bsf:a aac_adtstoasc z.mp4

  But the resulting file z.mp4 shows first 2 seconds ofa.mp4 and then it starts b.mp4 but c.mp3 is still being played. I want that till c.mp3 is played a.mp4’s last frame should stay.

• Can't get video output on avi to mp4 conversion using ffmpeg

  15 avril 2019, par davecgs

  I am so frustrated with this problem. Any time I convert avi files to mp4 files, I can get the audio, but NO video. Here are the various switches I’ve tried. I don’t know how to resolve the situation. I’ve never had this problem with mpg, mov or any other format, but AVI is frustrating.

  Doing this in php but I’ve also done it from the command line.

  (NOTE : I’ve also tried it with NO extra parameters letting ffmpeg do the full conversion).

  (NOTE : It does play the original avi file in any desired Windows or Linux player as is so I know there are is no damage to the original file, but I want to convert to mp4 for the web).

  (Final Note* : when using aac it warns of too many bits ...clamping to max if that helps)

  Here’s the code :

  $InputFile - some avi file. I have a ton of them and they all do the same thing.
  
  
  
  $OutputFile - same name but with an mp4 extension
  
  
  
  $Parameters are various switches I've used. 
  
  
  
  shell_exec ("ffmpeg -i  " . $InputFile . ' ' . $Parameters . ' ' . $OutputFile);
  
  
  
  $Parameters =  " -profile:v baseline -pix_fmt yuv420p ";
  
  
  
  $Parameters = " -acodec copy -vcodec copy ";
  
  
  
  $Parameters = " -c:v libx264 -c:a libfaac -movflags +faststart ";
  
  
  
  $Parameters = " -c:v libx264 -c:a aac -strict experimental -movflags +faststart ";
  
  
  
  $Parameters = " -c:v libx264 -c:a -acodec aac libfdk_aac -movflags +faststart ";
  
  
  
  $Parameters = " -c:v libx264 -preset slow -crf 18 -c:a libmp3lame -b:a 128k -f mp4 ";
  
  
  
  $Parameters =  " -c:v libx264 -crf 19 -preset slow -c:a aac -strict experimental -b:a 192k -ac 2 ";  

  I really don’t get why I only get an audio output. I can see it in VLC player, but, of course that’s not my goal. I want it to mp4 to see it on a webpage.

  I welcome any help !