[mythtv-users] NVDEC: is there something wrong with it?

James Abernathy jfabernathy at gmail.com
Sun Nov 15 20:30:09 UTC 2020

On Sun, Nov 15, 2020 at 12:20 PM Mark Kendall <mark.kendall at gmail.com>

> On Tue, 10 Nov 2020 at 14:27, Jim Abernathy <jfabernathy at gmail.com> wrote:
> >
> > I just put together a new workstation where I will be watching TV with
> > Mythtv-frontend when not using it for other things.
> >
> > It's a 6 core Ryzen 5 3600 with a Nvidia GT-1030 fanless GFX card.
> >
> > After the initial install of mythtv-frontend I started playing videos
> > with the default settings of NVDEC.  That worked fine on HD 1080i
> > content but when I tried a sub-channel where the video was 720x480 at 30, I
> > immediately noticed that the video paused and played every few seconds
> > and never got better.
> >
> > When I changed the video profile to High Quality OpenGL it worked
> > perfectly on all video types.
> >
> > So I'll leave it that way, but why would NVDEC be so bad on 480i
> content??
> >
> Jim
> A little late to the party but, thinking about it, there are 3 possible
> issues:-
> - as others have mentioned the 'old' nvidia mpeg2 decoding problem.
> You don't mention what the source material is other than the
> resolution - but I would expect that to present itself as corrupted
> video frames rather performance issues.
> - deinterlacer. NVDEC has an awkward deinterlacer setup and there is
> also the possibility it is falling over on a particular stream. I
> would try going into the details of the video display profile and
> disable the 'Prefer driver deinterlacers' option. That should give you
> nvdec decoding with OpenGL shader deinterlacers - if that works then
> the problem is in the deinterlacers.

This had no effect.

> - Stuarta A noticed an issue recently with some NVDEC problems which
> we tracked down to the number of video buffers in use. We didn't
> really finish the conversation but my testing with a 1030 works with
> just about everything I can throw at it - whereas Stuart (with a
> different nvidia card) had to make some source code adjustments to get
> playback to work smoothly.
> Can you post some 'mythfrontend -v playback' logs for a stream that
> does not play well?
> Thanks and regards
> Mark

When I looked at the logging I saw a lot of video behind audio and I went
in and changed the audio read ahead to 400ms and that fixed it. Not sure
why putting in a faster CPU and Motherboard made any difference when the
Nvidia card remained the same??


Jim A
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