[mythtv-users] v4l Framegrabber Video Quality

[Brian Wood]

On Monday 24 August 2009 12:53:23 James Crow wrote:
> Hello all,
>
> I recently lost my PVR-500 encoder and rather than purchase a new analog
> recorder I am falling back to the framegrabbers built into my Pinnacle
> 800i QAM/ATSC cards.
>
> With the PVR-500 bitrate cranked up to 6000-9000 the video was as good
> as the cable fed directly into the TV. With the mpeg4 settings on 5000
> the quality is still well below the PVR recordings.
>
> I think I have enough CPU for mpeg4 (Athlon 64 x2 3800+ 2.0GHz). I have
> searched the archives and played with the Recording Profile options, but
> am still not able to get decent quality from the framegrabbers. Does
> anyone have some pointers or settings I should try to improve the quality?
>
> I am willing to trade increased disk space for better quality
> recordings. I do not store any shows on external media and only watch
> shows from a Myth FE.
>
> Any suggestions?

Just a few questions to think about:

Obviously any sort of encoding can't make things better than the input video. 
Have you looked at the output of your frame grabber with xawtv or some such 
display program? Does that look as good as you think it should? Do you have 
sufficient level going into the capure card?

What sort of problems are you seeing on your recordings? Is it macro blocking 
or other digital artifacts, or is it random noise or some other analog type 
problem? Does it just look "soft", which can be an indication of too low a 
bitrate.

Have you tried the RTjpeg option to see if it looks better than the mpeg4? The 
file sizes will be bigger, but you said you don't care about that.

What's your CPU usage while encoding? If it's very high you may be dropping 
frames.

-- 
Brian Wood
beww at beww.org