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• utvideoenc : Enable support for multiple slices and use them

  14 février 2014, par Jan Ekström

  utvideoenc : Enable support for multiple slices and use them
  The official Ut Video decoder only threads with slices, thus until
  
  now any files encoded by the libavcodec encoder have only been
  
  decodable with a single thread. The default slice count is now
  
  set to subsampled_height / 120.
  Also sets slices to 1 for the Ut Video encoder tests to keep them
  
  green.
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/utvideoenc.c
  • [DH] tests/fate/utvideo.mak

• 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 ?

  


• How to set H264 NVENC encoding parameters to output high-quality video stream ?

  8 février 2021, par fredirty2017
  

  • I use NVENC (nvEncodeAPI) interface hardware encoding H264, and then RTMP to stream out, when using ffplay to pull the stream to watch, I found that the picture is obviously distorted : the green lines become sharper ? the text color becomes lighter and blurred, it is not improved even if I increase the video bitrate to 3Mbps(720P). I also know that H264 encoding is lossy, and some information will be discarded.

  


  • Then I try to adjust the NV_ENC_CONFIG_H264_VUI_PARAMETERS parameter : when set color-space to "pc, bt709", there are some minor improvements. Maybe the color-space setting has more potential for improvement ? For NVENC encoding, is there a higher video clarity setting scheme ? I don't know how much space for technical improvement is here ?

based on the code : https://github.com/obsproject/obs-studio/blob/master/plugins/obs-ffmpeg/obs-ffmpeg-nvenc.c