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• How to create an animated GIF using FFMPEG with an interval ?

  26 octobre 2014, par Jeff Wilbert

  Hello fellow overflowers,

  A brief overview of what I’m trying to accomplish ; I have a site that will accept video uploads, uploads get converted into the mp4 format to be uniformed and playable on the web using one of the many available players. That part is all fine and dandy.

  The problem now is I want to show the user a short scaled preview (animated gif) of the video before they click to play it. The code I’m working with now is

  ffmpeg -i test.mp4 -vf scale=150:-1 -t 10 -r 1 test.gif

  Which works for creating a scaled animated gif with a fixed width of 150px at a rate of 1 frame per second but its only an animation of the first 10 seconds of the video. I’m trying to do something that spreads out the frame gap to cover the whole video length but create an animated gift that’s no more then 10 seconds long.

  For example say I have a video that’s 30 seconds I want the gif to be 10 seconds long but cover frames of the entire 30 seconds so it might start at frame 3 or 3 seconds in and create a frame in the gif, then at 6 seconds in the video create another frame, then 9 seconds in another, and so forth where the final outcome is

      example video 30 seconds long          example video 1 minute 45 second long 
  
  
  
  video position - gif frame/per second      video position - gif frame/per second
  
        00:03:00   1                               00:10:50   1
  
        00:06:00   2                               00:21:00   2
  
        00:09:00   3                               00:31:50   3
  
        00:12:00   4                               00:42:00   4
  
        00:15:00   5                               00:52:50   5
  
        00:18:00   6                               01:03:00   6
  
        00:21:00   7                               01:13:50   7
  
        00:24:00   8                               01:24:00   8
  
        00:27:00   9                               01:34:50   9
  
        00:30:00   10                              01:45:00   10
  
  
  
    3 second interval between frames         10.5 second interval between frames

  Where you end up with an animated gif that’s 10 seconds long showing a preview of the entire video no matter the length of it. Which basically just boils down to
  video length / 10 (length of desired animated gif) = interval to use between frames but I don’t know how I can use that data to accomplish my problem...

  So does anyone have an idea or suggestion on how this can be accomplished with relative ease ? I can probably do it by calculating the length through code and running a command to extract each individual frame from the video that’s needed then generate a gif from the images but I’d like to be able to do it all with just one command. Thanks.

• lavf/matroskaenc : use mkv_check_tag_name consistently

  6 septembre 2016, par Rodger Combs

  lavf/matroskaenc : use mkv_check_tag_name consistently
  Previously, we used a different list of checks when deciding whether to
  
  write a set of tags at all than we did when deciding whether to write an
  
  individual tag in the set. This resulted in sometimes writing an empty
  
  tag master and seekhead. Now we use mkv_check_tag_name everywhere, so
  
  if a dictionary is entirely composed of tags we skip, we don’t write a
  
  tag master at all.
  This affected the test file, since "language" was on one list but not
  
  the other, so we were writing an empty tag master there. The test hash
  
  is updated to reflect that change.
  

  • [DH] libavformat/matroskaenc.c
  • [DH] tests/fate/matroska.mak

• MP4 moof fragment headers

  23 juillet 2019, par Ariana

  I have a MP4 parser software that get’s a fragmented .mp4 video, parses the MOOV and fragment headers and streams it. I have generated a .mp4 file myself using FFMPEG and MP4Box/bento4, but the software has problems processing it.

  ffmpeg -i input.mp4 -g 25 -c:v libx264 -c:a copy out1.mp4
  
  
  
  mp4fragment out1.mp4 --fragment-duration 1000 --track 'video' output.mp4

  Using the MP4 Explorer software, I noticed in my generated .mp4 file, for all moof.traf.trun, sample duration is set to 0, but in the Track Fragment Header box, it sets the default_sample_duration to 512. While in the another .mp4 file which works fine, there is no default_sample_duration field, but each individual sample has a duration of size 512. Looks like this might cause the problem. The right figure shows the working mp4, and the left one is my generated mp4.

  Is this an update in the newer versions of FFMPEG (or MP4Box or bento4) ? Is there any ways to force setting the sample duration in samples ?

  My .mp4 file

  The working .mp4 file