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• Stretch Subtitles Timing by Factor

  3 août 2022, par Matt McManis

  I'm muxing an mkv video, but the Subtitle .ssa file is out of sync by around 1 second by the end of the video.

  



  Delaying the subtitles by 1 second in the beginning is not enough, the timing needs to be stretched to fix an exponentially growing delay. Sync starts out fine in the beginning, but a few milliseconds delay multiplies for each minute that passes.

  



  I fixed them using MKVToolNix with Stretch 0.999.

  



  ---

  



  How can I stretch Subtitles using FFmpeg ?

  



  I saw here how to stretch audio by a factor the same way. ffmpeg, stretch audio to x seconds

  



  I'm using something like this :

  



  ffmpeg -y 

-fflags +genpts 

-i "video.m4v"  
-i "audio.ac3" 
-i "subs.ssa" 

-c:v copy 
-c:a copy 
-c:s copy 

-map 0:v? 
-map 1:a? 
-map 2:s?

"video.mkv"


  



  I used -itsoffset -00:00:01.000 to remove a gap in the beginning, but it does not stretch.

  


• How the ffmpeg fix is leading to clearing of teletext subtitles ? [closed]

  9 avril 2024, par adarsh

  Im working on the teletext subtitle feature and faced with subs not clearing issue.
https://sourceforge.net/p/zapping/bugs/203/
The player is using ffmpeg and libzvbi library.

  


  Luckily, this issue was fixed in ffmpeg- https://github.com/FFmpeg/FFmpeg/commit/b1e0e216462a989a39e7b413aef6d32f8cedc154

  


  and also in zvbi :
https://github.com/zapping-vbi/zvbi/commit/40a6ab0200c46b67b059b5b1fb15793ce780892a

  


  I know the root cause and fix in zvbi library, and how it is ignoring c4 flag in case the same page no.

  


  But i want to understand how the ffmpeg fix is working ?

  


• Ffmpeg can't convert at 24fps AND burn a subtitles

  14 novembre 2020, par Oshida_BCF

  i like to save my anime but i don't like when the subs are softburned and if the video is in mkv (it's heavier)

  


  so i made some .bat that encode the video and burn the subtitles.

  


  cd To convert
for %%a in ("*.mkv") do ffmpeg -i "%%a" -vf subtitles="%%a" -crf 18 -c:v libx264 -c:a aac -b:a 256k ../Converted/"%%~na.mp4"
pause


  


  this command burn the subtitles and it's perfect

  


  cd To convert
for %%a in ("*.mp4") do ffmpeg -i "%%a" -filter:v fps=fps=24 -crf 18 -c:v libx264 -c:a aac -b:a 256k ../Converted/"%%~na.mp4"
pause


  


  this one encode at 24 fps and it's perfect too

  


  but this one

  


  cd To convert
for %%a in ("*.mkv") do ffmpeg -i "%%a" -vf subtitles="%%a" -crf 18 -c:v libx264 -c:a aac -b:a 256k -filter:v fps=fps=24 ../Converted/"%%~na.mp4"
pause


  


  doesn't work.

  


  and i have no idea

  


  it convert the video in mp4, at 24fps
but it "forgot" the subtitles

  


  do there is some commands that aren't compatible and cancel each other ?

  


  for now i burn the sub on the video and i convert at 24 fps after.
but being able to do the 2 at the same time would save me a lot of time.