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• using ffmpeg scale filter , how to scale a sequence of images with dynamic sizes

  3 avril 2019, par user651177

  as the title asked , I am looking for a method that scales a sequence of images with dynamic sizes ,
  say i have a video stream containing tens or hundreds frames , I want to scale these frames in increasing or decreasing sizes , for example size of frame-1 is 1.25 times of size of frame-0, and size of frame-2 is 1.25 times of size of frame-1, and so on , but the scale filter seems to have no a frame-n parameter in the scaling expression , how can i do this ,

  please help

• ffmpeg extract first subtitle for given language or fix mismapped tracks

  11 mars 2023, par iarwain8a

  I'm developing a server to encode any given video and I need to extract its subtitles.

  


  I've tried something like this which worked :

  


  ffmpeg -i pipe:0 -map 0:s:1 -c:s webvtt -f segment -segment_list_flags +live -segment_time 60 -segment_list subs_eng.m3u8 -segment_format webvtt subs_eng.vtt -loglevel debug


  


  This encodes from srt, into webvtt, the second track which happens to be in this video an English subtitle. But very quickly I ran into a problem in which the tracks mappings are not numbered correctly for this video, for example, the (eng) track should be "-map 0:s:2", but it's "-map 0:s:1" as I've said before, and the (bul) track, which should be "-map 0:s:4" is actually "-map 0:s:2".

  


  Stream #0:0: Video: h264 (High), yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn (default)
  Stream #0:1(eng): Audio: eac3, 48000 Hz, 5.1(side), fltp, 768 kb/s (default)
  Stream #0:2(eng): Subtitle: subrip
    Metadata:
      title           : English
  Stream #0:3(eng): Subtitle: subrip
    Metadata:
      title           : English [SDH]
  Stream #0:4(bul): Subtitle: subrip
    Metadata:
      title           : Bulgarian (Bulgaria)


  


  Given said problem I tried something like this :

  


  ffmpeg -i pipe:0 -map 0:s:m:language:eng -c:s webvtt -f segment -segment_list_flags +live -segment_time 60 -segment_list subs_eng.m3u8 -segment_format webvtt subs_eng.vtt -loglevel debug


  


  Which didn't work because I can't or don't know how, to actually select the first result of this "-map 0:s:m:language:eng" if there is more than 1 "eng" sub track. Is there a way to do this ?
Or the alternative should be : Is there a reason why the metadata of this file is mismapped ? If so is there a way to detect it, to then do something about it ? or have it fixed ?

  


• ffmpeg extract first subtitle for given language or fix missmaped tracks

  11 mars 2023, par iarwain8a

  I'm using developing a server to encode any given video and I need to extract its' subtitles.

  


  I've tried something like this which worked :

  


  ffmpeg -i pipe:0 -map 0:s:1 -c:s webvtt -f segment -segment_list_flags +live -segment_time 60 -segment_list subs_eng.m3u8 -segment_format webvtt subs_eng.vtt -loglevel debug


  


  This encodes from srt, into webvtt, the second track which happens to be in this video an english subtitle. But very quickly I ran into a problem in which the tracks mappings are not numbered correctly for this video, for example, the (eng) track should be "-map 0:s:2", but it's "-map 0:s:1" as I've said before, and the (bul) track, wich should be "-map 0:s:4" is actually "-map 0:s:2".

  


  Stream #0:0: Video: h264 (High), yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn (default)
  Stream #0:1(eng): Audio: eac3, 48000 Hz, 5.1(side), fltp, 768 kb/s (default)
  Stream #0:2(eng): Subtitle: subrip
    Metadata:
      title           : English
  Stream #0:3(eng): Subtitle: subrip
    Metadata:
      title           : English [SDH]
  Stream #0:4(bul): Subtitle: subrip
    Metadata:
      title           : Bulgarian (Bulgaria)


  


  Given said problem I tried something like this :

  


  ffmpeg -i pipe:0 -map 0:s:m:language:eng -c:s webvtt -f segment -segment_list_flags +live -segment_time 60 -segment_list subs_eng.m3u8 -segment_format webvtt subs_eng.vtt -loglevel debug


  


  Which didn't work because I can't or don't know how, to actually select the first result of this "-map 0:s:m:language:eng" if there is more than 1 "eng" sub track. Is there a way to do this ?
Or the alternative should be : Is there a reason why the metadata of this file is missmapped ? If so is there a way to detect it, to then do something about it ? or have it fixed ?