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• how the packuswb instruction works ? (in low level bit operation)

  17 avril 2019, par MaikonNascimento

  Studying ffmpeg convertion from yuv to rgb , I came across the equation being implemented in assembly, yuv2rgb_template.c located in ffmpeg/libswscale/x86.

  I want to know how the instruction packuswb works ? Google says it :

  Converts 4 signed word integers from mm and 4 signed word integers from mm/m64 into 8 unsigned byte integers in mm using unsigned saturation.

      DEST[7:0] ← SaturateSignedWordToUnsignedByte DEST[15:0];
  
      DEST[15:8] ← SaturateSignedWordToUnsignedByte DEST[31:16];
  
      DEST[23:16] ← SaturateSignedWordToUnsignedByte DEST[47:32];
  
      DEST[31:24] ← SaturateSignedWordToUnsignedByte DEST[63:48];
  
      DEST[39:32] ← SaturateSignedWordToUnsignedByte SRC[15:0];
  
      DEST[47:40] ← SaturateSignedWordToUnsignedByte SRC[31:16];
  
      DEST[55:48] ← SaturateSignedWordToUnsignedByte SRC[47:32];
  
      DEST[63:56] ← SaturateSignedWordToUnsignedByte SRC[63:48];

  Since I dont know Assembly x86, it is even hard to simulate it or debug the current code.

  I want to know how they fit 16 bits in 8 bits ?

• FFMPEG - Palettegen for animations is not working

  18 juillet 2018, par deanhodges

  I have a script taken from the correct answer at https://superuser.com/questions/1002562/convert-multiple-images-to-a-gif-with-cross-dissolve, but I am getting no results.

  Even copying the code word for word does not work for me.

  However, if I run $ffmpeg = shell_exec("ffmpeg -i images/image001.jpg -vf palettegen palette_test.png"); on a single image, it works fine. But because I need it for an animation, I need to create a pallete for all images.

  Unless of course, on each image in the GIF sequence I can load a new palette ?

  $q = "ffmpeg -f image2 -framerate 0.5 -i ../view/client/files/".$dir."/%*.jpg -i palettePro.png -lavfi paletteuse -y .." . $save_path . '/' . $filename . " -report";

• Revision da58436f43 : Subsampling aware allocs and bitstream Make framebuffer allocations according t

  7 mai 2013, par John Koleszar

  Changed Paths :
   Modify /vp9/common/vp9_alloccommon.c

  
   Modify /vp9/common/vp9_blockd.h

  
   Modify /vp9/common/vp9_mbpitch.c

  
   Modify /vp9/common/vp9_onyxc_int.h

  
   Modify /vp9/common/vp9_postproc.c

  
   Modify /vp9/decoder/vp9_decodframe.c

  
   Modify /vp9/encoder/vp9_bitstream.c

  
   Modify /vp9/encoder/vp9_encodeframe.c

  
   Modify /vp9/encoder/vp9_firstpass.c

  
   Modify /vp9/encoder/vp9_lookahead.c

  
   Modify /vp9/encoder/vp9_lookahead.h

  
   Modify /vp9/encoder/vp9_onyx_if.c

  
   Modify /vp9/vp9_cx_iface.c

  
   Modify /vp9/vp9_iface_common.h

  
   Modify /vpx_scale/generic/yv12config.c

  
   Modify /vpx_scale/yv12config.h

  
   Modify /vpxdec.c

  
  
  Subsampling aware allocs and bitstream

  Make framebuffer allocations according to the chroma subsamping
  factors in use. A bit is placed in the raw part of the frame header for
  each of the two subsampling factors. This will be moved in a future
  commit to make them part of the TBD feature set bits, probably only set
  on keyframes, etc.

  Change-Id : I59ed38d3a3c0d4af3c7c277617de28d04a001853