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• Add buffering to real time input stream with c++ ffmpeg

  7 octobre 2018, par Joel

  I am writing a c++ program in which I am handling a real time udp video stream with the ffmpeg library.

  The video input fps is 25 frames per second in avarage. The gap between two frames can be 10 , 20, 40 milliseconds, but sometimes it can be around 80 milliseconds.
  In those times, when the gap is around 80 milliseconds, the video seems choppy or stuck,

  When I open the same stream with the ffplay player(using the ffplay.exe), using a simple
  "ffplay.exe udp ://ip:port" command, the video has a little delay (around 50 millisends) with respect to the origin stream, but it runs much more smoothly.

  Can I set a buffering time or any minimal delay so that the delay between the frames will be much more steady, in my c++ program ?
  If so, how can I do this ?

  Thanks,
  Joel

• Using an IF-Statement inside a drawtext (FFMPEG)

  22 janvier 2020, par MonsterDruide1

  I’m currently trying to implement a timer on a video with FFMPEG, so it should start at 00.00 and start timing after a number of frames and stop timing again after a set amount of frames. So the timer should work like this :

  00:00 00:00 00.00 (start timing) 00.01 00.02 [...] 05.88 05.89 (stop timing) 05.89 05.89 05.89

  So far I’ve got the following as (minimal) command :

  ffmpeg -i input.mp4 
  
  -filter_complex "[0:v]drawtext=fontfile='C\\:font.ttf':
  
  text='%{eif\\:n/30\\:d\\:2}\\:%{eif\\:((mod(n,30))/30)*100\\:d\\:2}':
  
  fontcolor=black:fontsize=55:x=(1705.5-(text_w/2)):y=(1000.5-(text_h/2)),format=yuv420p" 
  
  -pix_fmt yuv420p -c:a copy out.mp4

  There is some more stuff inside of the filter_complex, so I can’t replace that with -vf or similar.

  Thanks for all of your help !

• Calling ffmpeg kills script in background only

  14 mai 2014, par TimD

  I’ve got a python script that calls ffmpeg via subprocess to do some mp3 manipulations. It works fine in the foreground, but if I run it in the background, it gets as far as the ffmpeg command, which itself gets as far as dumping its config into stderr. At this point, everything stops and the parent task is reported as stopped, without raising an exception anywhere. I’ve tried a few other simple commands in the place of ffmpeg, they execute normally in foreground or background.

  This is the minimal example of the problem :

  import subprocess
  
  
  
  inf = "3HTOSD.mp3"
  
  outf = "out.mp3"
  
  
  
  args = [    "ffmpeg",
  
              "-y",
  
              "-i",   inf,
  
              "-ss",  "0",
  
              "-t",   "20",
  
              outf
  
          ]
  
  
  
  print "About to do"
  
  
  
  result = subprocess.call(args)
  
  
  
  print "Done"

  I really can’t work out why or how a wrapped process can cause the parent to terminate without at least raising an error, and how it only happens in so niche a circumstance. What is going on ?

  Also, I’m aware that ffmpeg isn’t the nicest of packages, but I’m interfacing with something that has using ffmpeg compiled into it, so using it again seems sensible.