[mythtv-users] Playback quality questions

Fedor Pikus fpikus at gmail.com
Mon Jun 27 17:26:30 UTC 2005

Now that I got Myth to display on my 32" TV and got rid of the ground
loop, I can see some artifacts and distortions in TV playback which I
did not notice earlier (TV is 32" CRT connected via SVideo, capture is
PVR350 and PVR150, TVout is NVidia 6200). Any hints or suggestions are

1) TV playback does not use about 1/2" on the bottom of the screen.
Only TV does not, Myth GUI is full-screen, DVD/video is full screen,
but when I watch TV there is a dark band below the picture. I tried TV
playback settings, specifically overscan and displacement. Y overscan
stretches the picture and makes the top of the picture go above
screen, but does not affect the lower edge. Y displacement does not do
anything at all, I tried -50 and +50 and the picture does not move.

2) Depending what's in the movie, I may see rapidly flashing or
scrolling horizontal bands. Usually not in all areas of the screen,
dark areas seem to show more of them, but if they were covering all
screen there would be at least 20 of the bands, may be more.
Everything I read on the list suggests deinterlacing issue, so I tried
enabling deinterlacing in TV settings. I tried kernel and bob options,
both seem to make the flashing bands slightly worse. I have denoise3d
filter enabled, I tried without it, other than slightly more noise
makes no difference.

3) While quality of the recordings is good, it degrades markedly after
transcoding. I use default values in all transcoding profiles. After
transcoding from MPEG2 to MPEG4 (bitrate 2200) the picture is
distorted in a way which is hard to describe exactly, but the first
reaction I had when I saw it was "pastel". The image has a "painterly"
look, with desaturated colors applied in broad blocky swatches. This
is most pronounced on faces and fast-moving objects. Cartoons are not
affected at all. Transcoding from MPEG2 to RTJPEG causes similar
distortions but in much smaller amounts. Funny thing is, I had this
system connected to a 21" VGA monitor when I was building it, and I
did not see any of that stuff. Must be the larger screen I guess.

Fedor G Pikus (fpikus at gmail.com)

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