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• Overlaying one video on another one, and making black pixels transparent

  25 janvier 2023, par Michael A

  I'm trying to use FFMPEG to create a video with one video overlayed on top another.

  



  I have 2 MP4s. I need to make all BLACK pixels in the overlay video transparent so that I can see the main video underneath it.

  



  I found two ways to overlay one video on another :

  



  First, the following positions the overlay in the center, and therefore, hides that portion of the main video beneath it :

  



      ffmpeg -i 1.mp4 -vf "movie=2.mp4 [a]; [in][a] overlay=352:0 [b]" combined.mp4 -y


  



  And, this one, places the overlay video on the left, but it's opacity is set to 50% so at least other one beneath it is visible :

  



  ffmpeg -i 1.mp4 -i 2.mp4 -filter_complex "[0:v]setpts=PTS-STARTPTS[top]; [1:v]setpts=PTS-STARTPTS, format=yuva420p,colorchannelmixer=aa=0.5[bottom]; [top][bottom]overlay=shortest=0" -acodec libvo_aacenc -vcodec libx264 out.mp4 -y


  



  My goal is simply to make all black pixels in the overlay (2.mp4) completely transparent. How can this be done.

  


• How can I extract all the keyframes from an MP4 video using ffmpeg ?

  3 juillet 2013, par Konstantin

  I would like to extract all keyframes from a video in BMP format for further processing. I managed to investigate this command :

  ffmpeg -skip_frame nokey -i videofile.mp4 -vf select='eq(pict_type\,I),setpts=N/(25*TB)' -q 1  ./%09d.bmp

  It works on all video files, except on MP4 and MKV files. Instead of it extracts all frames from the MP4 files, and additionally I got a lot of error messages :

  [h264 @ 0x90d80a0] concealing 1200 DC, 1200 AC, 1200 MV errors in P frame
  
  [h264 @ 0x90c4ce0] concealing 1200 DC, 1200 AC, 1200 MV errors in B frame
  
  [h264 @ 0x90d80a0] concealing 1200 DC, 1200 AC, 1200 MV errors in B frame
  
  [h264 @ 0x90d7500] Cannot use next picture in error concealment
  
  [h264 @ 0x90d7500] concealing 1200 DC, 1200 AC, 1200 MV errors in P frame

  What can I do to make it work also on MP4 files, or what other utility / method (mencoder / vlc) should I use to achieve my goal ?

• Passing variable (streamkey) inside ffmpeg command, wildcard name

  7 septembre 2022, par Kirk

  I want to pass in incoming stream to another server (from RTMP to SRT) and keep using the same streamkey using the following command :

  


  ffmpeg -fflags +genpts -listen 1 -re -i rtmp://0.0.0.0/publish/live/STREAMKEY -acodec copy -vcodec copy -strict -2 -y -f mpegts srt://1.1.1.1:30000?streamid=publish/live/STREAMKEY

  


  If I hard-code the streamkeys it works perfectly. The problem here is that the streamkey should be variable/wildcard. So basically this should work with any streamkey instead of hard-coding the stream key into the command. The incoming RTMP stream key should then be used to stream to the SRT server.

  


  So I guess the steps to check would be :

  


  

  • Is it possible to use wildcard naming in the command for the input RTMP stream ?

  


  • Is it possible to use that wildcard as a variable which is used in the forwarding to the SRT server part of the command ?

  


  


  Combining both would be the goal but not sure if even just one of these steps is possible.

  


  Thanks in advance for any hints.