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• How to detect audio volume using humble-video library ?

  21 octobre 2016, par Sonny MT

  I’m coding a Java sample to get audio volume data (in decibel) from a video file for some analysis using "ffmpeg" functions.
  It is workable using "ffmpeg" command line, as below :

  ffmpeg.exe -af volumedetect -f null -y null -i d:\test.mp4

  Output of ffmpeg.exe :

  video:3358kB audio:158568kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
  
  
  
  [Parsed_volumedetect_0 @ 00000000006fe580] n_samples: 81186816
  
  
  
  [Parsed_volumedetect_0 @ 00000000006fe580] mean_volume: -29.1 dB
  
  
  
  [Parsed_volumedetect_0 @ 00000000006fe580] max_volume: 0.0 dB
  
  
  
  [Parsed_volumedetect_0 @ 00000000006fe580] histogram_0db: 437
  
  
  
  [Parsed_volumedetect_0 @ 00000000006fe580] histogram_1db: 914
  
  
  
  [Parsed_volumedetect_0 @ 00000000006fe580] histogram_2db: 1486
  
  
  
  ...
  
  
  
  [Parsed_volumedetect_0 @ 00000000006fe580] histogram_7db: 19764
  
  
  
  [Parsed_volumedetect_0 @ 00000000006fe580] histogram_8db: 31078
  
  
  
  [Parsed_volumedetect_0 @ 00000000006fe580] histogram_9db: 45821

  I’ve found that humble-video is a good Java wrapper of ffmpeg with samples at https://github.com/artclarke/humble-video/blob/master/humble-video-demos/src/main/java/io/humble/video/demos/DecodeAndPlayAudio.java

  How and where can I get those audio volume data (same as volumedetect option) with humble-video ?

• How do I mix multiple audio tracks mit FFMPEG and adjust each volume ?

  4 avril 2022, par doppelzwei

  Let's say I have an input .mp4 file that contains 4 audio tracks.
How can I change their volumes independently and convert it to a new file that just contains all the 4 audio tracks mixed together and stored in the first audio track ? For example I want the first, second and third audio tracks from the input file to be double their original volume and the fourth to be half its original volume, all saved in the output files first audio track. How would that command look like ?

  


• 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