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• FFmpeg : Trying to fade out first and later fade back in doesn't work [duplicate]

  6 septembre 2023, par Paul S

  While I just became a registered user on the site, I've been utilizing Stack Overflow for years, virtually always being able to find solutions to problems I've encountered. Unfortunately, not this time ; I have encountered a problem with the ffmpeg video fade filter. There are lots of previously proposed issues along with their solutions, but none (that I can find) that address a twist that I have.

  


  Most questions ask, "how do I fade in", or "how do I fade out", and "how do I fade in at the beginning and fade out at the end." If I want to fade in and later fade out, my below code works just fine.

  


  ffmpeg -ss 00.0 -accurate_seek -to 15.0 -i My.Test.File.mkv -c:v h264 -vf fade=t=in:st=0:d=2,fade=t=out:st=13:d=2 -b:v 825k -s 1280x720 -r 29.97 -c:a aac -ar 44100 -ac 2 -b:a 96k output.mp4


  


  However, I actually want to fade out somewhere in the middle, and then fade back in shortly after, and that doesn't seem to work. I structured the ffmpeg command as so :

  


  ffmpeg -ss 00.0 -accurate_seek -to 15.0 -i My.Test.File.mkv -c:v h264 -vf fade=t=out:st=6:d=2,fade=t=in:st=9:d=2 -b:v 825k -s 1280x720 -r 29.97 -c:a aac -ar 44100 -ac 2 -b:a 96k output.mp4


  


  This fails and yields a completely blank video. I've also tried some -filter_complex variations, but get similar results ; fading in and later fading out works, but fading out and later fading in does not.

  


  I'm using the latest ffmpeg windows version on Windows 10. I would have attached a sample video file but I'm seeing how to do that. It is not the original video file that started my issue, but it does duplicate the issue. Not sure what other info might help in coming up with a solution. Thoughts ?

  


• FFmpeg WebM format not flushing packets after encoding each frame

  27 décembre 2020, par ciclopez

  I'm using FFmpeg to encode into VP9/WebM a raw video input coming from a pipe. Then in my implementation I send encoded frames through a socket in Python as soon as they are available (I need it as closest to realtime as possible), but to make it simpler I will omit that part and just write a file to disk, as the problem I'm having is also reproduced this way.

  


  Ok, let's show the command :

  


  ffmpeg -y -f:v rawvideo -c:v rawvideo -s 640x360 -pix_fmt bgra -r 60 -an -i - \
-b:v 2M -pix_fmt yuv420p -c:v libvpx-vp9 -quality realtime -speed 15 \
-flush_packets 1 -f webm /path/to/some/directory/test.webm


  


  I'm feeding the pipe from Python and checking the file size after each frame. The problem is that the file doesn't grow in size after each frame, but in 'blocks' of 128 frames (except for the first time that it flushes 25 frames at once).

  


  As I understand it, this shouldn't be happening as I'm using the flag -flush_packets 1.

  


  I also tried with other container formats like avi, and then it correctly flushes every frame (except for the first 25 frames like WebM, don't know why is that). So it seems related to how WebM muxes video frames.

  


  I've also tried by using ffmpeg's library directly with the help of pyav and writing to an in-memory file instead of disk, but had exactly the same problem, it flushes the same 128 frame blocks no matter what bitrate, resolution or flags I use.

  


  Does anybody know any flag to avoid flushing in blocks with WebM ?

  


  Where does that 25/128 frame interval come from ?

  


  Thanks !

  


• Concatenate two mp4 files using ffmpeg

  24 mars 2018, par Mark L

  I’m trying to concatenate two mp4 files using ffmpeg. I need this to be an automatic process hence why I chose ffmpeg. I’m converting the two files into .ts files and then concatenating them and then trying to encode that concated .ts file. The files are h264 and aac encoded and I’m hoping to keep the quality the same or as close to original as possible.

  ffmpeg -i part1.mp4 -vcodec copy -vbsf h264_mp4toannexb -acodec copy part1.ts
  
  ffmpeg -i part2.mp4 -vcodec copy -vbsf h264_mp4toannexb -acodec copy part2.ts
  
  cat part1.ts part2.ts > parts.ts
  
  ffmpeg -y -i parts.ts -acodec copy -ar 44100 -ab 96k -coder ac -vbsf h264_mp4toannexb parts.mp4

  Unfortunately I’m getting the following error message coming back from ffmpeg during encoding :

  [h264 @ 0x1012600]sps_id out of range
  
  [h264 @ 0x1012600]non-existing SPS 0 referenced in buffering period
  
  [h264 @ 0x1012600]sps_id out of range
  
  [h264 @ 0x1012600]non-existing SPS 0 referenced in buffering period
  
  [NULL @ 0x101d600]error, non monotone timestamps 13779431 >= 13779431kbits/s    
  
  av_interleaved_write_frame(): Error while opening file

  This happens about half way through encoding which makes me think that you can’t concat two .ts files together and have it work.