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• How to compress video with uniform blur being the only side effect of compression ?

  5 janvier 2020, par Kukuster

  The point is to somehow compress a video file, significantly reducing bitrate but somehow without changing its apparent quality, and because it would fit the design, I thought I will blur the video. In raster image processing I guess, it would be closer to the mean blur, or kind of like being behind turbid glass effect.

  Ideally, I would like to be able to choose between compressing more with more strong blur and compressing less with less strong blur, all look pretty in any case.

  I tried some ffmpeg postprocessing libraries including fspp, spp, uspp (takes a long time to render), etc. I almost reached the goal using fspp with parameters 5:60:15. But blur was either very strong for certain objects or left other undesired artifacts. Although uspp does a good job and looks pretty, it leaves about half of the image in frames unblurred, while I’m looking for more uniform blur across the frame. Because sometimes it takes a lot of time, I didn’t try all the features of uspp.

  Here is my ffmpeg input data about the video streams :

    Duration : 00:01:03.02, start : 0.000000, bitrate : 4010 kb/s
      Stream #0:0(und) : Video : h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 3870 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc (default)
      Metadata :
        handler_name : VideoHandler
      Stream #0:1(eng) : Audio : aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 133 kb/s (default)
      Metadata :
        handler_name : SoundHandler
  

  Edit : example input and output :
  
  

• Seek function of HTML5 video and Maximum Keyframe Interval in video encoding compression

  20 décembre 2019, par Sanxofon

  This is a very specific question about how the seek function (of an HTML5 video element) interprets a video, in this case one in WEBM format and what specific relationship it has with the Maximum Keyframe Interval in the process of coding of said video.

  I’ve made this fiddle to show what I mean :

  https://jsfiddle.net/sanxofon/hctuxo3e/

  What it does : The idea is to control the position of a paused video with the scroll wheel of the mouse ... in addition, each frame of the video is copied to a canvas element, but I think that has no relation. I mention it just in case.

  What to watch : In Chrome (v66) and slightly less in Firefox (v59) the scrolling looks pretty good when the video is encoded with a Maximum Keyframe Interval of 6 or less, but jumps are appreciated when the interval is every 24 frames or more. This is noticeable in the video and even more on the canvas.

  FFMPEG : When encoding a video with FFMPEG this is achieved with the option -g6 or -g24 of Maximum Keyframe Interval. However, the file becomes heavier as we decrease the interval. It can be seen that there is no difference between both formats when the video is in play.

  You can switch the video in the snippet with the buttons.

  • Case 1 : When we use the video encoded with -g 6 the video scrolling is acceptable but the size increases : 6.229 Mb.

  FFMPEG string used :

   ffmpeg -i INPUT.MOV -c: v libvpx -qmin 0 -deadline best -qmax 50 -crf 1 -b: v 100K -g 6 test / video_g6.webm

  • Case 2 : When we use the video encoded with -g 24 the displacement is not smooth and suffers from jumps but the size decreases : 4,477 Mb.

  FFMPEG string used :

   ffmpeg -i INPUT.MOV -c: v libvpx -qmin 0 -deadline best -qmax 50 -crf 1 -b: v 100K -g 24 test / video_g24.webm

  Why does this happen ?

  What about -keyint_min or -force_key_frames ? Do they have any positive effect ? Is it better to use something like cgop (closed gop) ?

  I would appreciate some reference of consultation on this subject or a more or less detailed explanation of this relationship for both the WEBM container and for MP4 and OGG video.

  I am not looking so much for a magical ffmpeg chain (although I would appreciate it) but rather an explanation of how this relationship between the keyframes and the seek of a javascript video works.

  Thank you very much for reading here.

  P.S. One more thing, if the seek function only stops in a keyframe, is it possible that this frame has more quality than the others so that the quality increases when the video stops ?

• avformat/matroskadec : Add a fate test for CodecPrivate compression

  7 décembre 2019, par Andreas Rheinhardt

  avformat/matroskadec : Add a fate test for CodecPrivate compression
  This test contains a track with zlib compressed CodecPrivate in addition
  
  to compressed frames ; the former was unchecked before.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] tests/fate/matroska.mak
  • [DH] tests/ref/fate/matroska-zlib-decompression