[mythtv-users] MPEG-4 codec and interlaced video: Cr/Cb not encoded properly?

[rosenbla at uchastings.edu]

Could this be the cause of the very noticable tearing effect some of us are seeing when there is horizontal panning in the video? Do the maintainers of the MPEG-4 compressor know about this? 

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I figured I'd try encoding some video captured by MythTV to DVD, and I think 
I've run across a problem in the way the color information is encoded by the 
MPEG-4 encoder. It doesn't show up in the NuppelVideo compressor, but in 
the MPEG-4 compressor, the Cr & Cb components of the bottom field don't line 
up with the Y component if there's any substantial amount of motion between 
the fields. They line up pretty nicely with the top field, though, which 
would indicate that the compressor is trying to treat interlaced video in 
the same manner as non-interlaced video. It appears to subsample Cb & Cr by 
reading every other scanline, which effectively tosses out the bottom-field 
color information. Is this a shortcoming of the MPEG-4 compressor, or is 
MythTV not initializing it or sending data to it properly? 

_/_ Scott Alfter 
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(IIGS( http://alfter.us/ Top-posting! 
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