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• Output to pipe and file at the same time even if pipe isn't accepting inputs

  5 juillet 2018, par Eduardo Perez

  So, I made a script for Cygwin that uses Windows’s ImageMagick and FFmpeg, but I am not sure if the results here will also apply for bash on Linux. So, what the script does is I have some cartoon video files and I’m using Waifu2x to enhance and upscale the images to 4K, and then using ImageMagick to pipe it to FFmpeg, which is also used to resize it to 3840x2160 in case the resolution is slightly different. Here’s a small script I wrote for this example to simplify how it outputs to FFmpeg, as the real script is extremely lengthy and complex.

  #!/bin/bash
  
  fun(){
  
  convert out.png JPG:-|tee "$outfile"
  
  }
  
  fun|ffmpeg -f image2pipe -r 60 -i - -c:v libx265 -movflags +faststart "$outputfile"

  Now, what I noticed is that if FFmpeg fails to encode, the function continues but fails to output to $outfile. What I want to do is have it able to output to that file in case the encoding fails since I also write all the images to a cache folder for FFmpeg to run through in case the encoding fails, but I also want to write to both the pipe for FFmpeg and the file at the same time. What seems to be happening is that the command tee appears to be refusing to write to the file if it can’t write to the pipe. I’m not sure if this behavior is intended, and/or if it also does this on Linux bash. How can I get around this and have it write to the file even if it can’t write to the pipe, but write to both at the same time rather than writing to the file and attempting to read it back to the pipe ?

• ffplay : how does it calculate the fps for playback ?

  21 octobre 2020, par Daniel

  I'm trying to playback a live media (h264) which is produced by a hardware encoder.

  


  The actual desired FPS on the encoder is set to 20, and when checking the logs of the encoder it prints "FPS statistics" every minute :

  


  2020-10-21 17:26:54.787 [  info] video_stream_thread(),video chn 0, fps: 19.989270
2020-10-21 17:27:54.836 [  info] video_stream_thread(),video chn 0, fps: 19.989270
2020-10-21 17:28:54.837 [  info] video_stream_thread(),video chn 0, fps: 20.005924
2020-10-21 17:29:54.837 [  info] video_stream_thread(),video chn 0, fps: 19.989270
2020-10-21 17:30:54.888 [  info] video_stream_thread(),video chn 0, fps: 19.989274
2020-10-21 17:31:54.918 [  info] video_stream_thread(),video chn 0, fps: 19.989264


  


  You can see it's varying, but not too much around 20.

  


  Question1 : Is this normal ? Or it should be exactly 20 every time ? To avoid confusion : I'd like to know if by the standard of H264, can this be accepted as a valid stream or this violates some
rule ?

  


  I'm trying to playback this stream with ffplay :

  


  $ ffplay rtsp://this_stream
Input #0, rtsp, from 'xyz'
  Metadata:
    title           : 
    comment         : substream
  Duration: N/A, start: 0.040000, bitrate: N/A
    Stream #0:0: Video: h264 (Constrained Baseline), yuv420p(progressive), 640x360, 25 fps, 25 tbr, 90k tbn, 180k tbc


  


  The thing is that ffplay thinks this is a stream with 25fps. And it also plays 25 frames each sec, causing the stream to stall and buffer in every few seconds.

  


  I believe the fps is calculated by some pts/dts values in the stream itself, and it's not hardcoded. Am I wrong here ?

  


  If I'm not wrong, why does ffplay thinks this stream runs at 25fps, whereas it only runs at (around) 20 ?

  


• Evolution #2608 (Fermé) : visiteurs

  22 mars 2012, par cedric -

  faut relire le thread de 6 mois sur le bandeau... les visiteurs concernent l’activité publique du site et sont donc rangés dans le menu Activité