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• How can I create a FULL copy of a decoder ?

  28 avril 2015, par damicolo

  I’m writing a video decoder (using FFMPEG/AVCodec) for a custom implementation of an mpeg4 video stream. The peculiarity of this video stream is that it could split into many "son" streams creating many P frames based on the same parent. The video stream I’m trying to decode is actually a sort of "video tree". Something like this :

  I <--P <--P <---------------------P <-------------- P <------------ P
  
             \ <--P <--P <--P        \ <--P <--P       \ <--P <--P 

  I’ve already wrote a basic decoder which works fine when I decide to follow one path, the problem is when I try to follow more than one path in the video tree. At this point I need to "fork" my decoder to follow two different video streams. the split could occur not only after a key frame, but even after a P frame, so I need to duplicate the AVCodecContext (I use avcodec_copy_context) but it seems to create new decoder from a clean status.. it seems to ignore the previous video status, so the decoded P frames are "applied" to an empty video frame.
  Probably copying the context using avcodec_copy_context is not enough... Any suggestion ? How can I duplicate the context and the complete status of the decoder ?
  Or, is there any other way to decode my stream using references ?
  Thanks !

• SEI type 63 truncated ? Best way to convert non-mp4 to web optimized mp4 ?

  28 mars 2017, par Chris Palmer Breuer

  I am trying to convert any video file to a web optimized mp4 format and I tried this sample mkv file to make some tests.

  The following is a message I keep getting for multiple minutes over and over again :

  [NULL @ 0x7f979c00a600] SEI type 63 size 4208 truncated at 88
  
  [h264 @ 0x7f979b06a000] SEI type 63 size 4208 truncated at 80
  
  [NULL @ 0x7f979c00a600] SEI type 63 size 4208 truncated at 88
  
  [h264 @ 0x7f979b002c00] SEI type 63 size 4208 truncated at 80
  
  [NULL @ 0x7f979c00a600] SEI type 63 size 4208 truncated at 528
  
  [h264 @ 0x7f979b027400] SEI type 63 size 4208 truncated at 520

  The code that I use the convert the mkv file is :

  ffmpeg -i test.mkv -movflags faststart -vcodec h264 -acodec aac -strict -2 test-ffmpeg.mp4

  Now, my question is, am I doing anything wrong ? Should I just ignore those messages as the file gets created ? Is there a more efficient way to create a web optimized mp4 file from a non mp4 file ?

  Thanks so much for the help.

• Repeating images in a ffmpeg -i %04d.png pattern

  2 mars 2021, par Basj

  I'm making a video of 20 seconds at FPS=25, with 500 frames which are 0000.png, 0001.png, ..., 0499.png. This works :

  


  ffmpeg -framerate 25 -i images/%04d.png out.mp4


  


  but in fact there are only a few changes in the video, in my case at frames 0000, 0122, 0288, 0312, 0450. In the meantime the PNG are identical.

  


  Problem : it's always slow to generate 500 PNG files when only 5 different files would be enough ! I would like to generate only those 5 PNG files, and generate the video from them.

  


  When I try the command above with images/ containing only 0000.png, 0122.png, 0288.png, 0312.png, 0450.png and not the 495 others, obviously it fails with :

  


  


  [image2 @ 00000000006d4040] Could not open file : images/0001.png

  


  


  Question : is there a way to tell ffmpeg to ignore missing frames and use the latest available frame instead of failing, when using -i images/%04d.png ?

  


  If not, what alternative is there to generate the video with only these 5 PNG that should arrive at a precise timeframe ?