• Compression Techniques

  Systematic artefacts from 10bit source

  Posted by Thomas Demirian on January 8, 2015 at 1:18 pm

  When encoding from a 10 bit source file, compression / color artifacts appear. From what I can see, the problem lies in the “dc precision” command “-dc”. I have tried different combinations and these are my results.

  On HD encodings ”-dc8” will give you nice clean solid colors without artifacts. But gradients and shading will suffer and be rougher.

  On HD encodings ”-dc11” will give you bad compression and color artifacts that look very systematic as you can se on attached pictures. But the Gradients look nice and smooth.

  On SD encodings ”-dc8” will give you nice clean solid colors without artifacts. But gradients and shading will suffer and be rougher.

  On SD encodings ”-dc9” will give you bad compression and color artifacts that look very systematic. But the Gradients look nice and smooth.

  Why is this? And can it be fixed? From other encoding software’s if I mimic the settings, all the encodings looks nice in all cases. So it seems that there is a bug in ffmpeg.

  Here is an example of the ffmpeg command I use:

  -i INPUT -vcodec mpeg2video -aspect {$aspectRatio} -r 25 -pix_fmt yuv422p -timecode_frame_start 0 -minrate 150000k -maxrate 150000k -b 150000k -intra -flags +cgop -flags2 +ivlc+non_linear_q -dc 11 -sc_threshold 1000000000 -qscale 1 -qmin 1 -qmax 12 -bufsize 47185920 -rc_init_occupancy 47185920 -rc_buf_aggressivity 0.25 -s {$resolution} -vframes {$frameDuration} -an OUTPUT

  If you want to try it yourself, make sure your source is 10bit, like Uncompressed 10 bit YUV.

  To better see the artefacts, zoom in close in the grey solids.

  

  Thomas Demirian replied 11 years, 4 months ago 1 Member · 0 Replies
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