[mythtv-users] Jittery playback after moving from .11 to .14

[Leif Pearson]

From: "Leif Pearson" <leifontheroad at hotmail.com>
Sent: Tuesday, March 16, 2004 3:22 PM


> I recently rebuilt my MythTV box to move from .11 to .14 and have found
that
> the playback on live and recorded TV is jittery. What I mean by jittery is
> that every 5 seconds or so, the playback seems to skip a few frames, or
play
> them in fast-motion (hard to tell which).  The sound manages to stay
> in-synch with the video.  One other problem is that commercial skip
doesn't
> work very well - it will catch the first or second break, but as the show
> progresses, it is less able to flag commercials.  Playback and commercial
> skip both worked great under my .11 setup.
>
> I suspect these two issues are related, and am hoping someone out there
has
> some ideas. For what it's worth, I am not very experienced with Linux,
just
> experienced enough to setup a MythTV box with a reasonable amount of
> head-banging.
>
> Here are my hardware specs:
>
> - Shuttle SB51G mobo
> - 2ghz P4
> - WinTV Go capture card (bt878 chipset)
> - Nvidia MX 440SE video card (64 MB, I think)
> - This is a dedicated MythTV box, so there's nothing else eating CPU
>
> Software Specs:
> - Fedora Core 1
> - Axel Thimm's 2.4.22-1.2174.nptl_37.rhfc1.at kernel
> - Followed Jarod Wilson's terrific guide for installation, pretty much
> followed it exactly
>
> I haven't changed any of my HW configuration since I had things up and
> running under .11, so the only major changes are software related.  The
> major changes in software are:
>
> - Running under Fedora instead of RH9
> - Installed using Jarod Wilson's terrific guide (as I did for .11), but
for
> 14 I took advantage of Axel Thimm's ATrpms kernel, including the custom
> video drivers that I believe he created.  I wasn't able to get the Nvidia
> driver from Axel's .11 kernel to compile and play nicely (kept crashing),
so
> I used as much of Axel's ATrpms as I could, and then installed the Nvidia
> drivers from the Nvidia website over the top of his ATrpms.
>
> The areas that I am most suspicious of are a) the custom Nvidia drivers,
and
> b) changes in MythTV from .11 to .15.  I have scoured the archives for
> ideas, and tried most of those (messing with video recording quality, all
> the options in the front end), but to no avail - no matter what I tried,
the
> jittery playback was still present, and the commercial skip didn't work
very
> well.  I've gone back to the standard settings that are in place when
MythTV
> is first installed, and have found those to perform the best (in other
> words, I don't believe I need to have a funky configuration to make this
> work).
>
> Does anyone have any thoughts on what I could try next?  I'm thinking that
> going back to the stock Nvidia drivers is the most prudent next step, but
> wanted to see if anyone else had experienced similar problems.
>
> Thanks alot,
>
> - Leif

Doh!  I figured out part of this - it looks like I did not have my hard
drives enabled for DMA.  I had to disable this when I loaded the Fedora Core
because it complained about not being able to copy from the cdrom to my
harddrive (gave me some 'you are probably out of disk space' message).
Anyway, I just found this in the MythTV FAQ:

http://www.mythtv.org/docs/mythtv-HOWTO-20.html#Setting_DMA
I checked and my hard drives were not enabled for DMA.  I have now enabled
DMA using the instructions in the FAQ and my jittery playback is gone, and
commercial skip seems to be working ok.

Funny, I scoured the archives for answers, but didn't even think to look
back at the FAQs.  That'll teach me a lesson...