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• aacenc_tns : redo coefficient quantization and decision making

  12 septembre 2015, par Rostislav Pehlivanov

  aacenc_tns : redo coefficient quantization and decision making
  This finally (and again) gets rid of basically everything the
  
  specifications say about how TNS should be done. The main
  
  problem used to be that a single filter was used for all
  
  coefficients which despite being explicitly recommended by
  
  the specifications usually sounds wrong, therefore it’s
  
  a corner case in the current TNS implementation.
  This commit also changes the coefficient bit size, as apparently
  
  it’s better to use lower precision in case the windows are eight
  
  short. This is apparently what fdk_aac uses, looking at the bit
  
  stream and makes sense. Also the order when 8 SHORT windows happen
  
  is important as 7 was too much and according to PSNR was worse
  
  while 5 is just about correct.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] libavcodec/aacenc_tns.c
  • [DH] libavcodec/aacenc_tns.h

• ffmpeg, how to generate small clip from a video as thumbnail ? [on hold]

  26 janvier 2017, par Ayman Elgohary

  FFmpeg CLI, how to generate short preview video from a video ?

  I was tried lots of CLI but none of them is working.

• Writing linear float range to openEXR turns out non linear

  3 avril 2022, par Chryfi

  I am writing the linearized depth buffer of a game to openEXR using FFmpeg. Unfortunately, FFmpeg does not adhere to the openEXR file specification fully (like allowing unsigned integer for one channel) so I am writing one float channel to openEXR, which is put into the green channel with this command -f rawvideo -pix_fmt grayf32be -s %WIDTH%x%HEIGHT% -r %FPS% -i - -vf %DEFVF% -preset ultrafast -tune zerolatency -qp 6 -compression zip1 -pix_fmt gbrpf32le %NAME%_depth_%d.exr.

  


  The float range is from 0F to 1F and it is linear. I can confirm that the calculation and linearization is correct by testing 16 bit integer (per pixel component) PNG in Blender compositor. The 16 bit integer data is written like this short s = (short) (linearzieDepth(depth) * (Math.pow(2,16) - 1)) whereas for float the linearized value is directly written to OpenEXR without multiplying with a value.

  


  However, when viewing the openEXR file it doesn't have the same "gradient" as the 16 bit png... when viewing them side by side, it appears as if the values near 0 are not linear, and they are not as dark as they should be like in the 16 bit png.
(And yes, I set the image node to linear), and comparing it with 3d tracking data from the game I cant reproduce the depth and cant mask things using the depth buffer where as with the png I can.

  


  How is it possible for a linear float range to turn out so different to a linear integer range in an image ?