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• libavcodec/xsubenc.c : Fix bounding box coordinates

  7 novembre 2013, par Erik Olofsson

  libavcodec/xsubenc.c : Fix bounding box coordinates
  Fix coordinates of the lower right corner of the text area.
  
  Note that the coordinates are redundant as the size and
  
  position of the text area are known.
  
  Many decoders (including Sony Playstation 3, VLC and FFmpeg)
  
  ignore the redundant coordinates.
  
  Some hardware decoders need them for correct playback.
  Verified on Philips DVD player models HTS7201 and DVP3380.
  Fixes ticket #3031
  Signed-off-by : Erik Olofsson <eaj.olofsson@gmail.com>
  
  Reviewed-by : Reimar Döffinger <Reimar.Doeffinger@gmx.de>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/xsubenc.c

• How do video encoding standards(like h.264) then serialize motion prediction ?

  12 août 2019, par Nephilim

  Motion prediction brute force algorithms, in a nutshell work like this(if I'm not mistaken) :

  



  

  1. Search every possible macroblock in the search window

  


  2. Compare each of them with the reference macroblock

  


  3. Take the one that is the most similar and encode the DIFFERENCE between the frames instead of the actual frame.

  


  



  Now this in theory makes sense to me. But when it gets to the actual serializing I'm lost. We've found the most similar block. We know where it is, and from that we can calculate the distance vector of it. Let's say it's about 64 pixels to the right.

  



  Basically, when serializing this block, we do :

  



  

  • Ignore everything but luminosity(encode only Y, i think i saw this somewhere ?), take note of the difference between it and the reference block

  


  • Encode the motion, a distance vector

  


  • Encode the MSE, so we can reconstruct it

  


  



  Is the output of this a simple 2D array of luminosity values, with an appended/prepended MSE value and distance vector ? Where is the compression in this ? We got to take out the UV component ? There seem to be many resources that take on the surface level of video encoders, but it's very hard to find actual in-depth explanations of modern video encoders. Feel free to correct me on my above statements.

  


• avcodec/pngdec : support decoding sRGB chunks

  17 janvier 2023, par Leo Izen

  avcodec/pngdec : support decoding sRGB chunks
  If an sRGB chunk is present in the PNG file, this commit will cause the
  
  png decoder to ignore the cHRM and gAMA chunks and tag the resulting AVFrames
  
  with BT.709 primaries, and ISO/IEC 61966-2-1 transfer. If these tags are
  
  present in the AVFrame, pngenc.c already writes this chunk, so no change was
  
  needed on the encode-side.
  The PNG spec does not define what happens if sRGB and iCCP are present at
  
  the same time, it just recommends that this not happen. As of this patch,
  
  the decoder will have the ICC profile take precedence, and it will not tag
  
  the pixel data as sRGB.
  Signed-off-by : Leo Izen <leo.izen@gmail.com>
  

  • [DH] libavcodec/pngdec.c