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• How does ffmpeg read stdin pipe ?

  17 novembre 2017, par ciclopez

  I’m working on a Python script that generates an image sequence based on user real time remote interaction, and uses ffmpeg to compress and stream this image sequence over the network for the user to watch it.
  As soon as an image is generated the script writes it to ffmpeg’s stdin and this action is repeated inside a loop to form a video.

  I was wondering what happens when ffmpeg is busy processing the previous image when I write to stdin.

  • Does the .stdin.write() command block execution until ffmpeg finishes processing the previous image ? (Consequence of the pipe buffer filling up)
  • What’s the buffer size of subprocess.PIPE ?
  • Is it editable ?
  • Is it possible to overwrite this buffer if it’s full, instead of blocking execution ?
  • Does ffmpeg continually read it’s input in a parallel process and buffers it until it’s free to take care of it ?
  • If that’s the case, what’s the size of ffmpeg’s input buffer and how can I change it ?

  I’m asking this because I want to fully understand how the data travels between Python and ffmpeg to reduce the latency to its minimum.

  Here is the part of the code I’m using to start ffmpeg :

  cmd = ['ffmpeg',
  
      '-f', 'rawvideo',
  
      '-s', '%dx%d'%(width, height),
  
      '-pix_fmt', 'rgba',
  
      '-r', '%d'%fps,
  
      '-i', '-',
  
      '-an',
  
      '-vcodec', 'libx264',
  
      '-tune', 'zerolatency',
  
      '-preset', 'ultrafast',
  
      '-bf', '0',
  
      '-f', 'mpegts',
  
      'udp://xxx.xxx.xxx.xxx:xxxxx']
  
  
  
  proc = subprocess.Popen(cmd, stdin=subprocess.PIPE)

  And this is what I call inside a loop when I want to pass an image to ffmpeg :

  proc.stdin.write(image)

• Making youtube-dl download mp3's faster

  12 novembre 2017, par sciencelord

  It takes a long time to download mp3 songs using youtube-dl, and it takes even longer when downloading a bunch of mp3 songs. Is there a way to make it significantly faster ? I don’t mind reducing quality. I’ve been using the command below.

  youtube-dl --extract-audio --audio-format "mp3" --output "%(title)s.%(ext)s" "https://www.youtube.com/watch?v={videoid}

  I also took a look at this post :
  ffmpeg command for faster encoding at a decent bitrate with smaller file size

  But I wasn’t sure how to change the above command using the ffmpeg modifications.

  Thanks !

• Ffmpeg stream rtsp via h264 with low quality

  9 novembre 2017, par dscsdc

  When i stream rtsp with ffmpeg via upd i got lot of errors of error while decoding MB 48 31, bytestream. and i see the video with low quality.

  I stream with ffmpeg according to this command :ffmpeg -i rtsp://x.x.x.x/... http://y.y.y.y:zzzz

  On this way I send the data to ffserver and then I can watch the video via ffplay or vlc according to url :rtsp://w.w.w.w:(port)/live.h264
  (I have ffserve conf that stream to h264 file).

  When i stream via rtsp tcp all is fine, and i see the video well. but when i stream with rtsp udp i got video with very low quality, freezes or gets stuck.

  I want to understand 2 stuff :

  1. I know that udp is less reliability then tcp, but when i watch on stream from another streaming via rtsp udp i see the video with much more quality.
     is ffmpeg has a problem to stream udp or is that because i stream h264 with rtsp udp.
     What can i do to improve performance of ffmpeg with rtsp udp ?

  2. What does it matter witch type of file i stream (on rtsp udp) if this will be h264 or avi or mp4 or ffm or amp ?
     i see lot of streaming that stream amp , and another that streaming h264