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• ffmpeg filter_complex multiple overlays - why are they not syncing properly

  28 décembre 2023, par howdood

  I'm setting up live streaming using three overlaid inputs in ffmpeg. O:v is a webcam directly connected to the streaming box (a headless linux box) while 2:v and 3:v are ultra-low latency UDP streams from two remote R-Pis.

  


  The filter_complex argument I'm using (that works, with all three video inputs perfectly in sync) is
[0:v] fifo [v1] ;[2:v] fifo [v2] ; [3:v] fifo [v3] ;[v1]setpts=PTS-STARTPTS[sync1] ;[v2]setpts=PTS-STARTPTS[sync2] ; [v3]setpts=PTS-STARTPTS+5/TB [sync3] ;[sync1][sync2] overlay=x=W-w:y=H-h [out1] ;[out1][sync3] overlay=x=0:y=H-h [vfinal]

  


  Two questions about this :

  


  


  1. Why am I having to add +5/TB to [sync3] via setpts (in bold above) ? If I omit that, [3:v] is synced in to the stream noticeably ahead of the other two inputs. My best guess is that this may be to compensate for the processing time of the first overlay [sync1][sync2] which is introducing extra latency into that part of the stream. Is that right ?

     


  


  2. Importantly - the value of the extra pts compensation has to be dialed in by hand and will be specific to the underlying hardware used. Is there a way of getting ffmpeg to calculate this automatically so I don't have to worry about keeping in dialed in, in production ?

     


  


  


  Thanks for reading ! I'm at the limit of the ffmpeg docs here...

  


• Make an Alpha Mask video from PNG files

  15 juin 2019, par Archimedes Trajano

  For RenPy it uses the notion of an Alpha Mask video https://www.renpy.org/doc/html/movie.html#movie-displayables-and-movie-sprites

  I can convert the a bunch of PNGs with alpha channel to http://wiki.webmproject.org/howtos/convert-png-frames-to-webm-video I was wondering how to do the same sort of thing without creating another set of PNG files with just the alpha frame.

  I’ll be okay with something that uses imagemagik in the middle if needed.

• what is the best way to append a video file to multiple video files using batch file [on hold]

  5 avril 2017, par JAGGADAKU

  i am beginner with computer programming and i have knowledge of c/c++

  from [https://trac.ffmpeg.org/wiki/Concatenate][1] i have learned that how to merge video files using ffmpeg

  To list all video files containing in a folder

  (for %%i in (*.mp4) do @echo %%i) > mylist.txt

  to concatenate files

  ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.mp4

  This merges all files of a list to one single file.
  but How do i append one video file(main.mp4) at the starting of all the video files listed in mylist.txt ?

  can someone help me ?

  Hello there

  i have tried following code i don’t know what’s wrong with it but it is not `

  @echo off
  
  (for %%i in (*.mp4) do @echo %%i) > mylist.txt
  
  
  
  for /F "tokens=*" %%A in (mylist.txt) do (
  
      echo %%A
  
      ffmpeg -i "concat:main.mp4|%%A" -c copy  %%Aoutput.mp4
  
  
  
  )
  
  `