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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.

  


• Merge remote-tracking branch ’rbultje/vp9-32bit-lpf’

  27 décembre 2014, par Michael Niedermayer

  Merge remote-tracking branch ’rbultje/vp9-32bit-lpf’
  * rbultje/vp9-32bit-lpf :
  
    vp9/x86 : add myself to copyright holders for loopfilter assembly.
  
    vp9/x86 : make filter_16_h work on 32-bit.
  
    vp9/x86 : make filter_48/84/88_h work on 32-bit.
  
    vp9/x86 : make filter_44_h work on 32-bit.
  
    vp9/x86 : make filter_16_v work on 32-bit.
  
    vp9/x86 : make filter_48/84_v work on 32-bit.
  
    vp9/x86 : make filter_88_v work on 32-bit.
  
    vp9/x86 : make filter_44_v work on 32-bit.
  
    vp8/x86 : save one register in SIGN_ADD/SUB.
  
    vp9/x86 : store unpacked intermediates for filter6/14 on stack.
  
    vp8/x86 : move variable assigned inside macro branch.
  
    vp9/x86 : simplify ABSSUM_CMP by inverting the comparison meaning.
  
    vp8/x86 : remove unused register from ABSSUB_CMP macro.
  
    vp9/x86 : slightly simplify 44/48/84/88 h stores.
  
    vp9/x86 : make cglobal statement more conservative in register allocation.
  
    vp9/x86 : save one register in loopfilter surface coverage.
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/x86/vp9dsp_init.c
  • [DH] libavcodec/x86/vp9lpf.asm

• hevc : deobfuscate slice/tile boundary handling for DBF

  27 juillet 2014, par Anton Khirnov

  hevc : deobfuscate slice/tile boundary handling for DBF
  Use named constants instead of magic numbers, avoid using variables with
  
  inverse meaning from what their name implies.
  

  • [DBH] libavcodec/hevc.c
  • [DBH] libavcodec/hevc.h
  • [DBH] libavcodec/hevc_filter.c