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• Closed Captioned TS to Open Captioned MP4 (w/Accurate Positioning)

  19 décembre 2019, par Cody Greene

  I am attempting to convert closed captioned MPEG TS files to open captioned MP4s using ffmpeg.

  I am having trouble retaining the positioning of the captions.

  The closest I’ve gotten is with this simple script :

  ffmpeg -f lavfi -i movie=input.ts[out+subcc] -map 0:1 output.ass
  
  ffmpeg -i input.ts -vf "subtitles=output.ass" -c:v libx264 -pix_fmt yuv420p -b:v 8000k -c:a aac -b:a 192k target.mp4

  The result of this is the open captions are shifted FAR left and the bounding box draws black over the empty spaces left of wherever text is centered (ssa adds "/h", easily removed with sed, but then it’s left-aligned captions only)

  However, the vertical position, overall size, etc. all look great.

  Most subtitle formats force everything to the bottom center, but I’m trying to mimic the look of an open caption on the mp4 output.

  I’ve tried several formats with ccextractor and ffmpeg, but no luck. Any ideas what I’m doing wrong ?

• configure : Fix debugging on mingw-w64 with gdb

  29 mars 2016, par Alex Smith

  configure : Fix debugging on mingw-w64 with gdb
  The relocation hack broke debugging on mingw-w64 when using gdb.  This
  
  makes the reloc hack dependent on —disable-debug so it’s still enabled
  
  for release builds.
  This is simply an immediate fix for the issue of broken debugging, we
  
  should probably still look at the possibility of reverting it outright
  
  if it proves to be more trouble than it’s worth.  For now keeping it
  
  enabled for release builds is a reasonable trade off.
  Signed-off-by : Alex Smith <theryuu@warpsharp.info>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] configure

• C - FFmpeg changing the output stream codec_tag

  12 octobre 2020, par emdou

  I'm having fun with the FFmpeg library to better undestand it. A came across a hiccup when transmuxing from an mp4 to an mkv format. The error being that the mp4a tag is not supported :

  


  [matroska @ 0000000002f100c0] Tag mp4a incompatible with output codec id '86018' ([255][0][0][0])


  


  Now I handle it simply by changing the codec_tag in the output stream. To do so, I check the supported AVCodeTag structs in the AVOutputFormat of the output AVFormatContext. In my example I have :

  


  Video: avc1  -> Unsupported by mkv but does't make a fuss about it (changed to H264 tag 875967048)
Audio: mp4a  -> Unsupported by mkv and refuses transmuxing if not changed (changed to 0)


  


  For the .ts format neither is a supported codec tag but transmuxing works fine (mostly).

  


  The error is raised when trying to write the output file header.

  


  I'm really having trouble understanding what changing the codec_tag really does during transmuxing. What is really happening under the hood ?