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• Why are Cb and Cr planes displaced differently from lum by the displace complex filter in ffmpeg ?

  10 janvier 2024, par Neb

  I have a video encoded with the yuv420p pixel format and I want to displace its pixels. I'm using ffmpeg and its new displace filter. The filter takes as inputs (the video to be displaced and) two displacement maps respectively for X and Y axis. I decided to create the displacement maps directly into ffmpeg using the nullsrc video source filter and the geq filter to specify the value of the three planes : lum, Cb, Cr. The script is the following :

  



  ffmpeg INPUT.mp4 -f lavfi -i nullsrc=size=${WIDTH}x${HEIGHT}:d=0.1,geq='lum=128+30*sin(2*PI*X/400):Cb=128+30*sin(2*PI*X/400):Cr='128+30*sin(2*PI*X/400)' -f lavfi -i nullsrc=size=${WIDTH}x${HEIGHT}:d=0.1,geq='lum=128+30*sin(2*PI*X/400):Cb=128+30*sin(2*PI*X/400):Cr=128+30*sin(2*PI*X/400)' -lavfi '[0][1][2]displace' OUTPUT.mp4


  



  I used the example provided in the documentation of ffmpeg, since the expression used in geq is irrelevant for the purposes of the problem.

  



  At the and of the computation, I get the pixels of the input video not properly displaced, meaning that I can clearly see a sort of ghost carrying-color-information video under a displaced but b/w one.
After some tests, I noticed that the displacemnt map created had only the luma plane displaced correctly while the chrominance planes were displaced, but differently from luma, which is the origin of the planes disalignment in the intput video as you can see in the following extract frames :

  



  

  



  I also noticed that the video describing the Cb and Cr planes of the displacement maps have half resolution of the luma plane.

  



  My question is : how can i setup correctly the Cr and Cb planes in the geq definition so that they are exactly identical to the luma plane ?

  



  It would be also great if someone could explain me why ffmpeg gives me an output so much different for luma and Cb, Cr planes even if the function provided is the same.

  



  If, it can help, i'm using ffmpeg 3.3-static build.

  



  Thanks for your time.

  


• Grep for a number between a certain range - Checking WAV Quality

  11 août 2014, par BT643

  I’m trying to write a regular expression (to be used in conjunction with ffmpeg, which can check that a WAV file is over a certain quality.

  The minimum should be :

  Audio Channels : 2 (Stereo)
  Audio Sample Rate : 44,100 Hz
  Audio Bitrate : 1411 Kbps
  Audio Bit Depth : 16 bit
  

  So I’ve tried the following commands so far :

  • /usr/local/bin/ffmpeg -i "/path/to/file.wav" 2>&1 | egrep 'stereo|2 channels'

  This works fine to get a stero (2 channel) WAV. I’m getting issues with the next part, searching between a range of numbers.

  • /usr/local/bin/ffmpeg -i "/path/to/file.wav" 2>&1 | egrep 'stereo|2 channels' | egrep '[41000-196000] Hz'

  Obviously this just searches each number individually, so it’s finding results if there’s a 4 OR 1 OR 0 OR 0 OR 0 etc...

  The bit rate and bit depth just needs to be OVER 1411 and 16 respectively.

  Thanks

  EDIT -
  Here’s the ffmpeg output for a low quality WAV which should be rejected :

  ffmpeg version git-2012-05-22-27127eb Copyright (c) 2000-2012 the FFmpeg developers
 built on May 22 2012 12:27:21 with gcc 4.6.1
 configuration: --enable-gpl --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libx264 --enable-nonfree --enable-postproc --enable-version3 --enable-x11grab
 libavutil      51. 53.100 / 51. 53.100
 libavcodec     54. 21.101 / 54. 21.101
 libavformat    54.  6.100 / 54.  6.100
 libavdevice    53.  4.100 / 53.  4.100
 libavfilter     2. 75.100 /  2. 75.100
 libswscale      2.  1.100 /  2.  1.100
 libswresample   0. 15.100 /  0. 15.100
 libpostproc    52.  0.100 / 52.  0.100
[wav @ 0x355b140] max_analyze_duration 5000000 reached at 5056000
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0, wav, from '/path/to/file.wav':
 Duration: 00:02:28.47, bitrate: 512 kb/s
   Stream #0:0: Audio: pcm_u8 ([1][0][0][0] / 0x0001), 32000 Hz, stereo, u8, 512 kb/s

• lavc/aacenc_utils : replace sqrtf(Q*sqrtf(Q)) by precomputed value

  1er mars 2016, par Ganesh Ajjanagadde

  lavc/aacenc_utils : replace sqrtf(Q*sqrtf(Q)) by precomputed value
  It makes no sense whatsoever to do this at each function call ; we
  
  already have a table for this.
  Yields a 2x improvement in find_min_book (x86-64, Haswell+GCC) :
  
  ffmpeg -i sin.flac -acodec aac -y sin.aac
  
  find_min_book
  
  old
  
      605 decicycles in find_min_book, 8388453 runs,    155 skips.9x
  
      606 decicycles in find_min_book,16776912 runs,    304 skips.9x
  
      607 decicycles in find_min_book,33553819 runs,    613 skips.2x
  
      607 decicycles in find_min_book,67107668 runs,   1196 skips.3x
  
      607 decicycles in find_min_book,134215360 runs,   2368 skips3x
  new
  
      359 decicycles in find_min_book, 8388552 runs,     56 skips.3x
  
      360 decicycles in find_min_book,16777112 runs,    104 skips.1x
  
      361 decicycles in find_min_book,33554218 runs,    214 skips.4x
  
      361 decicycles in find_min_book,67108381 runs,    483 skips.5x
  
      361 decicycles in find_min_book,134216725 runs,   1003 skips5x
  and more importantly a non-negligible speedup ( 8%) to overall AAC encoding :
  
  old :
  
  ffmpeg -i sin.flac -acodec aac -strict -2 -y sin_new.aac  6.82s user 0.03s system 104% cpu 6.565 total
  
  new :
  
  ffmpeg -i sin.flac -acodec aac -strict -2 -y sin_old.aac  6.24s user 0.03s system 104% cpu 5.993 total
  This also improves accuracy of the expression by 2 ulp in some cases.
  Reviewed-by : Derek Buitenhuis <derek.buitenhuis@gmail.com>
  
  Reviewed-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  
  Signed-off-by : Ganesh Ajjanagadde <gajjanag@gmail.com>
  

  • [DH] libavcodec/aacenc_utils.h