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• How to successfully decode ffmpeg frames with http timeouts without parsers

  28 août 2019, par igal k

  I’m facing a scenario where connectivity issues cause ffmpeg generate false / messed artifacts(frames) contrary to what the manual states.

  We use curl as our http transmitting library and ffmpeg as the processing library. To simulate network timeouts, I place several breakpoints in the AVIOContext which is passed to the AVFormatContext

  avformat_open_input('http://some.com/1.ts')
  
  while(!eof)
  
    av_read_frame
  
    av_send_packet
  
    while(!av_receive_frame)
  
       do_something
  
  close

  av_receive_frame should either return 0 upon success or error -35 for cases where additional data is needed.

  So after timeout-ing the session, ffmpeg can still somehow extract (av_receive_frame) the first frame even though it hadn’t have the chance to download / accumulate enough data.

  

  My question, without using parsers is there a way to validate that the decoder can successfully decode the packet ?

  "EDIT" : i saw that av_read_frame use parsing if AVStream::need_parsing attribute is anything than NONE, any ideas on how setting it up ?

• Conversion of mp3 to flac results in file with longer duration

  18 juin 2019, par ThaDon

  I’ve noticed that when I convert an mp3 file to flac, the duration reported in the flac file will often differ from that of the source mp3 file. Mostly this difference is negligible and can be ignored (perhaps a fraction of a second).

  However, there are times when the timing is off by several seconds, and this causes my processing pipeline quite a bit of problem.

  For instance, take this podcast episode for example. If I run it through ffmpeg, I can see that it has a duration of :

  Duration: 00:52:38.39, start: 0.000000, bitrate: 128 kb/s

  If I then convert it to flac using the following command :

  ffmpeg -i startups-for-the-rest-of-us-448.mp3 -ac 1 -ar 16000 -f flac output.flac

  I can see that the duration of the flac file is :

  Duration: 00:52:45.65, start: 0.000000, bitrate: 133 kb/s

  Note there is an error message during conversion that states :

  [mp3 @ 0x7fffd16d6780] Header missing
  
  Error while decoding stream #0:0: Invalid data found when processing input

  Does the difference in duration have have to do with the bitrate difference ? When I listen to the file it sounds identical, I’m assuming the flac version must be ever so slightly slower as to gain the extra 7 seconds over the course of the podcast.

• ffmpeg with "-pattern_type glob" and variable in bash script

  20 juin 2019, par KlausPeter

  I’m trying to let ffmpeg make a video of all pictures in a directory using the -pattern_type glob switch and "/foo/bar/*.jpg". This works well, if I execute the command manually für just one directory. For example :

  ffmpeg -framerate 35 -pattern_type glob -i '/root/webcam_test/2018-07-21/*.jpg' -vf scale=1280:-1 -c -c:v libx264 -pix_fmt yuv420p /root/clips/out01_cut.mp4

  However, if I do it in a bash script and set the path via a variable, according to ffmpegs output, the variable gets substituted correctly, but ffmpeg states that

  ’/root/webcam_test/2018-07-21/*.jpg’ : No such file or directory

  The part of the script looks like this :

  for D in `find /root/webcam_test/ -type d`
  
  do
  
      [...]
  
      cmd="ffmpeg -framerate 35 -pattern_type glob -i '$D/*.jpg' -vf scale=1280:-1 -c -c:v libx264 -pix_fm                                 t yuv420p /root/clips/$d_cut.mp4"
  
      echo $cmd
  
  [...]
  
  done

  Does anyone know how to make ffmpeg do its wildcard interpretation even if the path is constructed by a script and not just try to plainly use the given path ?
  Best regards and thanks in advance