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• FFMPEG : Get the Scene Change Detection value for all frame

  19 novembre 2016, par celacanto

  I’m trying to measure how much a movies is "fast" (more action in the screen and quick scene chances). I don’t want just a single value for the movie, but values along the movie to see how the action varies during it. After normalize the frame rate of the movies (10 fps), my idea is to compare each frame with the previous. I’m not only interest if the scene has changed, but also, if there was no cut, how much movement there is. Not only people/object movement but also, camera movement. In summary the paced (I think that the term) of the scenes.

  My idea was to use the scene function from ffmpeg as a metric. But looking at the document and examples online I’m thinking I can only use the value of the Scene Change Detection as a threshold to return frames informations, but I can’t get ffmpeg to return the value. Is that right ? There is any way I can make it return the value ?

• FFmpeg CRF control using x264 vs libvpx-vp9

  19 octobre 2016, par igon

  I have some experience using ffmpeg with x264 and I wanted to do a comparison with libvpx-vp9. I tested a simple single pass encoding of a raw video, varying the crf settings and presets both with x264 and libvpx-vp9. I am new to libvpx and I followed this and this carefully but I might have still specified wrong combination of parameters since the results I get do not make much sense to me.

  For x264 I did :

  ffmpeg -i test_video.y4m -c:v libx264 -threads 1 -crf <crf> -preset <preset> -y output.mkv 
  
  </preset></crf>

  and obtained the following results :

  codec  , settings                        , time        , PSNR      ,bitrate
  
  libx264,['-crf', '20', '-preset', 'fast'],13.1897280216, 42.938337 ,15728
  
  libx264,['-crf', '20', '-preset', 'medium'],16.80494689, 42.879753 ,15287
  
  libx264,['-crf', '20', '-preset', 'slow'],25.1142120361, 42.919206 ,15400
  
  libx264,['-crf', '30', '-preset', 'fast'],8.79047083855, 37.975141 ,4106
  
  libx264,['-crf', '30', '-preset', 'medium'],9.936599016, 37.713778 ,3749
  
  libx264,['-crf', '30', '-preset', 'slow'],13.0959510803, 37.569511 ,3555

  This makes sense to me, given a crf value you get a value of PSNR and changing the preset can decrease the bitrate but increase the time to encode.

  For libvpx-vp9 I did :

  ffmpeg -i test_video.y4m -c:v libvpx-vp9 -threads 1 -crf <crf> -cpu-used <effort> -y output.mkv 
  
  </effort></crf>

  First of all I thought from tutorials online that the -cpu-used option is equivalent to -preset in x264. Is that correct ? If so what is the difference with -quality ? Furthermore since the range goes from -8 to 8 I assumed that negative values where the fast options while positive values the slowest. Results I get are very confusing though :

  codec     , settings                      , time        , PSNR     ,bitrate
  
  libvpx-vp9,['-crf', '20', '-cpu-used', '-2'],19.6644911766,32.54317,571
  
  libvpx-vp9,['-crf', '20', '-cpu-used', '0'],176.670887947,32.69899,564
  
  libvpx-vp9,['-crf', '20', '-cpu-used', '2'],20.0206270218,32.54317,571
  
  libvpx-vp9,['-crf', '30', '-cpu-used', '-2'],19.7931578159,32.54317,571
  
  libvpx-vp9,['-crf', '30', '-cpu-used', '0'],176.587754965,32.69899,564
  
  libvpx-vp9,['-crf', '30', '-cpu-used', '2'],19.8394429684,32.54317,571

  Bitrate is very low and PSNR seems unaffected by the crf setting (and very low compared to x264). The -cpu-used setting has very minimal impact and also seems that -2 and 2 are the same option.. What am I missing ? I expected libvpx to take more time to encode (which is definitely true) but at the same time higher quality transcodes. What parameters should I use to
  have a fair comparison with x264 ?

  Edit : Thanks to @mulvya and this doc I figured that to work in crf mode with libvpx I have to add -b:v 0. I re-ran my tests and I get :

      codec     , settings                                 , time        , PSNR     ,bitrate
  
  libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '-2'],57.6835780144,45.111158,17908
  
  libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '0'] ,401.360313892,45.285367,17431
  
  libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '2'] ,57.4941239357,45.111158,17908
  
  libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '-2'],49.175855875,42.588178,11085
  
  libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '0'] ,347.158324957,42.782194,10935
  
  libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '2'] ,49.1892938614,42.588178,11085

  PSNR and bitrate went up significantly by adding -b:v 0

• Migration from FFMPEG 4.3.2 to 5.1.0 - Alternative to AVLockOp enum

  1er novembre 2022, par jd750

  A lot of classes and enums that I use in FFMPEG 4.3.2 were removed from the version 5. The enum AVLockOp is one of them. I looked online for a AVLockOp alternative in the version 5.1.0 but I didn't find any. Is there an alternative to AVLockOp in FFMPEG 5.1.0 ?

  


  I googled : "ffmpeg AVLockOp alternative", "ffmpeg AVLockOp deprecated", "ffmpeg 5.1 migration AVLockOp", etc...

  


  I didn't find what I was looking for. So stackoverflow is my last hope.
I'm looking for someone who had the same issue or someone that knows an alternative to replace AVLockOp in FFMPEG 5.1.