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• Parallel transcoding with FFmpeg on M1 Mac

  27 août 2021, par Pushkar

  I'm trying to determine how effective an M1 Mac would be for transcoding video using FFmpeg (specifically resizing and adjusting bitrate). I can do single transcodes using a command like this :

  


  ffmpeg -I in.mp4 -nostdin -c:v h264_videotoolbox -c:a copy -vf scale=1280:720 -b:v 8000k out.mp4


  


  Now, when I run this, I can see the process in Activity Monitor, but it shows significant CPU use but 0% GPU use, although it's certainly using some form of hardware acceleration (using libx264 instead of h264_videotoolbox is much slower).

  


  When I try running multiple processes concurrently, the timings suggest little evidence of parallel execution :

  


  





  


  


  


  


  



  


  


  


  


  


  


  


  


  


  


  


  


  Test	Timing
  convert single test file	6.8s
  convert file 5 times sequentially	33.6s
  convert file 5 times in parallel	31.5s

  


  


  Since the M1 chip is supposed to have 7 or 8 GPUs inside it, I expected to see quite good parallelism, so are there options which I'm missing which would :
  

  


  

  1. ensure that the transcoding is actually running on the GPU ?

  


  2. allow parallel execution across the multiple GPUs ?

  


  


• nested loop in bash shell

  17 juin 2015, par Tareq Suheimat

  I want to stream video using ffserver and then receive and download it using ffmpeg but first I want to add some noise to the link using netem and the wanted noise will be Bit error,so for the transmitter side there’s no problem the problem is at the receiver side
  so the first loop must contain the percentage numbers of the bit error like 0.2 0.4 0.6 0.8 and do the following command :

  tc qdisc change dev eth0 root netem corrupt 0.1%

  then for each one of the bit error values must repeat it for 10 times and for each try I must download the received video using the following command :

  ffmpeg -i rtsp://localhost:7654/test1-rtsp.mpg -acodec copy -vcodec copy output.mp4 

  so later I end up with too many videos to compare them later.

  please people help me it’s urgent !!!

  tell now I have this scratched code but I don’t know how to compile it together

  for i in {0.2 0.4 0.6 0.8}
  
  do
  
      tc qdisc change dev eth0 root netem corrupt ${i}%
  
  
  
      #(must repeat for each i the ffmpeg download command 10 times)
  
  
  
      #The download command
  
      for x in {1..N}
  
      do
  
          ffmpeg -i rtsp://localhost:7654/test-rtsp.mpg -acodec copy -vcodec copy tested${x}.mp4
  
      done

• Add Audio to video with existing audio using FFmpeg and change volume of of both audios

  14 juin 2017, par 1234567

  Add Audio to video with existing audio using FFmpeg and change volume of both audios

  I am using this command from ffmpeg to merge audio to video

  video.mp4 has video and audio, and audio.m4a only has audio

  ffmpeg -i video.mp4 -i audio.m4a -map 0:v -map 1:a -c copy -shortest output.mp4

  I want to merge audio to video but maintain audio from both video and the new audio file

  I also want to change the volume of audio file that I want to add from current file to 1.5 times

  and change the audio from the video file to 0.5 times

  how can we change the volume and still maintain new and old audio in the merged file