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• avformat/mov : fix hang while seek on a kind of fragmented mp4

  3 février 2019, par Charles Liu

  avformat/mov : fix hang while seek on a kind of fragmented mp4
  Binary searching would hang if the fragment items do NOT have timestamp for the
  
  specified stream.
  For example, a fmp4 consists of separated 'moof' boxes for each track, and
  
  separated 'sidx' for each segment, but no 'mfra' box.  Then every fragment item
  
  only have the timestamp for one of its tracks.
  Example :
  
  ffmpeg -f lavfi -i testsrc -f lavfi -i sine -movflags dash+frag_keyframe+skip_trailer+separate_moof -t 1 out.mp4
  
  ffmpeg -ss 0.5 -i out.mp4 -f null none
  Also fixes the hang in ticket #7572, but not the reason for having
  
  AV_NOPTS_VALUE timestamps there.
  Signed-off-by : Charles Liu <liuchh83@gmail.com>
  
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavformat/mov.c

• How to specify an offset and a seek position for a video stream of a mp4 container ?

  29 mai 2019, par maximedupre

  It seems like I can have one or the other (-ss or -itsoffset), but never both at the same time, or they kind of cancel each other.

  I create output.mp4 with this command :

  ffmpeg -i input.mp3 -itsoffset 4 -t 4 -ss 3 -i input.mp4 -c:v copy output.mp4

  With this command, I expect the audio to start playing right away, and the video to start playing 4 seconds later, seeked at 3 seconds into the video.

  However, when I play input.mp4, the video starts only one second later than the audio (as opposed to 4 seconds). I suppose it does a "offset - seek = 1" type of thing.

  How can I prevent the seeking from affecting the offset ?

  Cheers !

• ffmpeg fast but accurate seek in avi

  21 mars 2019, par C.M.

  I’ve built a small pipeline to automatically cut and enhance video files which I recorded.

  I detect scenes by using the ffmpeg’s select='gt(scene,0.4)',showinfo filter. After parsing these information I run ffmpeg for each scene to produce single video files for them, for example :

  ffmpeg -y -i test.avi -ss 00:00:00.00 -to 00:00:54.61 -c copy test_1.avi
  
  ffmpeg -y -i test.avi -ss 00:00:54.61 -to 00:01:38.21 -c copy test_2.avi
  
  ffmpeg -y -i test.avi -ss 00:01:38.21 -to 00:01:59.45 -c copy test_3.avi
  
  [...]

  As you can see I use the -ss and -to parameters to specify where the output files should start and end. This is working very well but it becomes very, very slow over time since my original file size is 50 gigabytes.

  I guess that -ss lets ffmpeg seek from the beginning of the original file to the start time as I can observe disk action when seeking.

  Placing the -ss param before the -i input file is faster but very inaccurate (off by some seconds).

  Is there maybe any trick to increase the cut/trim performance without losing the accuracy ?

  I also tried to convert the input file to MP4 which decreases the file size and seek time significantly. But then I had keyframe errors and I want to operate on the original files.

  Thank you !