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

James Abernathy jfabernathy at gmail.com
Sun Nov 15 21:19:17 UTC 2020

On Sun, Nov 15, 2020 at 3:30 PM James Abernathy <jfabernathy at gmail.com>

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

Everytime I go through one of these video playback issues with mythfrontend
I start getting really picky, so I'm testing everything with a critical
eye.  There is still something that is bothering me about what I'm seeing
on the GT-1030 on my new system. My test case today is NFL football. On the
closeup action shots the motion is just not perfectly smooth.  If I'm just
watching then I don't care, but when watching with a critical eye, it's not
perfect.  The only visual effect I can describe is on the sports new crawl
at the bottom of the screen. It will scroll along perfectly and then the
text will be jerky just a little, then go back to a perfectly smooth scroll.

I've tried High and Normal OpenGL, NVDEC, and VDPAU. All about the same..

My goal standard at this time is my Nvidia Shield TV. None of the issues I
tried to describe above exist at all on mythfrontend on the Shield TV or on
Leanfront on the Shield TV.

So I have a workable solution for my Mythtv frontend on my main TV, but It
just bothers me that a 6 core Ryzen 5 3600 and a GT-1030 aren't as good as
a $150 Android streaming box.

Jim A
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