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• FFMPEG - force webm clusters duration [closed]

  1er avril 2021, par Vlad Sineok

  in short, i'm modifying a game that uses a VP8 video format.
the original videos are at 25 fps and have all clusters of nice and perfect duration 0.96 seconds and contain 25 blocks each (except for that last cluster, which usually varies). also every cluster starts with a keyframe. (all that information i gathered using webm_info from google's libwebm repo)

  


  unless all of the requirements are met, the game struggles to play the webm file smoothly, so my own webm files stutter most of the time, because ffmpeg fails to create the correct clusters and mkclean doesn't help either.
so my question is : how would i force ffmpeg to make all clusters have that perfect duration ?
here's what my command currently looks like

  


  for %%f in (*.webm) do (
ffmpeg -y -i %%f -vcodec libvpx -cpu-used 1 -pass 1 -reserve_index_space 16384 -fflags +genpts -crf 15 -slices 8 -g 25 -keyint_min 25 -vprofile 1 -auto-alt-ref 1 -arnr-maxframes 5 -arnr-strength 3 -deadline good -vf scale=512:384,setsar=1:1 -vb 4000k -an -r 25 -movflags use_metadata_tags -f webm NUL && ^
ffmpeg -y -i %%f -vcodec libvpx -cpu-used 1 -pass 2 -reserve_index_space 16384 -fflags +genpts -crf 15 -slices 8 -g 25 -keyint_min 25 -vprofile 1 -auto-alt-ref 1 -arnr-maxframes 5 -arnr-strength 3 -deadline good -vf scale=512:384,setsar=1:1 -vb 4000k -an -r 25 -movflags use_metadata_tags -f webm %%~nf.webm
)


  


• problem : FFMPEG seeking with av_seek_frame using byte positions

  16 juillet 2012, par Nick Verlinden

  I am trying to get the av_seek_frame() function to go to a byte position I specify. I am implementing a frame accurate seeking mechanism for my application, and the way I see it, I will scan the entire video file, and store byte positions for each keyframe in a struct. I found out where to get the current byte position : AVPacket.pos. I now test this position with av_seek_frame like this :

  av_seek_frame( pFormatCtx, videoStream, 110285594, AVSEEK_FLAG_BYTE);

  However, this does not seem to do the right thing, when I call av_read_frame, it just starts with frame 23. If I do not seek, it starts at frame 1.

• How to convert messed-up .vtt sub file from youtube-dl —write-auto-sub download ?

  27 septembre 2023, par perry_the_python

  My goal is to download a YouTube video with auto-generated subtitles in a separate file like .vtt,.srt, etc.

  


  I am currently trying to achieve this with youtube-dl but I am open to other solutions if needed.

  


  When I run the following command, it downloads the video as .mp4 (which is fine) and a separate .vtt file, but the .vtt seems to be messed-up somehow and displays all the text for the whole clip at once instead of the specified times.

  


  Command I am running :

  


  youtube-dl --write-auto-sub https://www.youtube.com/watch?v=Roc89oOZOF4&list=PLJBo3iyb1U0eNNN4Dij3N-d0rCJpMyAKQ&index=45


  


  Downloads this .vtt :

  


  WEBVTT&#xA;Kind: captions&#xA;Language: en&#xA;&#xA;00:00:05.960 --> 00:00:08.290 align:start position:0%&#xA; &#xA;thank &lt;00:00:06.003><c>you  </c>&lt;00:00:06.046><c>ah </c>&lt;00:00:06.089><c>crap  </c>&lt;00:00:06.132><c>well </c>&lt;00:00:06.175><c>looks </c>&lt;00:00:06.218><c>like </c>&lt;00:00:06.261><c>the </c>&lt;00:00:06.304><c>good </c>&lt;00:00:06.347><c>Lord </c>&lt;00:00:06.390><c>just </c>&lt;00:00:06.433><c>sent  </c>&lt;00:00:06.476><c>me </c>&lt;00:00:06.519><c>a </c>&lt;00:00:06.562><c>conversation </c>&lt;00:00:06.605><c>starter </c>&lt;00:00:06.648><c>come </c>&lt;00:00:06.691><c>here  </c>&lt;00:00:06.734><c>Jesse </c>&lt;00:00:06.777><c>come </c>&lt;00:00:06.820><c>get </c>&lt;00:00:06.863><c>the </c>&lt;00:00:06.906><c>ball  </c>&lt;00:00:06.949><c>hmm</c>&#xA;&#xA;00:00:08.290 --> 00:00:10.549 align:start position:0%&#xA;thank you  ah crap  well looks like the good Lord just sent  me a conversation starter come here  Jesse come get the ball  hmm&#xA; &#xA;&#xA;00:00:10.549 --> 00:00:13.070 align:start position:0%&#xA; &#xA; &#xA;&#xA;00:00:13.070 --> 00:00:15.470 align:start position:0%&#xA; &#xA; &#xA;&#xA;00:00:15.470 --> 00:00:23.750 align:start position:0%&#xA; &#xA; &#xA;&#xA;00:00:23.750 --> 00:00:23.760 align:start position:0%&#xA; &#xA; &#xA;&#xA;00:00:23.760 --> 00:00:26.480 align:start position:0%&#xA; &#xA;&#xA;&#xA;&#xA;

  


  I have read that this may be done on purpose by YouTube.

  


  Even if this is true, is there any way to convert this .vtt to a usable format or simply download correctly-formatted auto-generated subtitles from YouTube ?

  


  Python, FFMPEG, cmd-line preferred, but anything is helpful !

  


  Thanks ! Any and all assistance is greatly appreciated !