[mythtv-users] Choppy Playback & prebuffering message

[Steven Adeff]

On 4/17/06, glen martin <lists at locutory.org> wrote:
> Scott Petler wrote:
> > After reading more about your particular machine, I think the issue is
> > even more likely due to
> > a pci bus bandwidth issue.  This is because your video card is PCI
> > rather than AGP.
> >
> > Having both the backend and frontend on the same machine is using up
> > your PCI bandwidth.
> > I would suggest a system with AGP video to keep your playback path off
> > of the PCI bus.
> >
> Interesting. What does this mean for 'modern' machines with PCI-E cards,
> or those with onboard video? Or mine, which has both (onboard video that
> can be overridden with a PCI-E16 card)? Is there something magic about
> AGP, and I should preferably replace my frontend with a mobo that
> supports AGP?

PCIE!=PCI. PCIE is faster than AGP, its one of the AGP replacement bus designs.


> lspci shows my onboard video and network and ide all on the same pci bus.
>
> My own situation is that I can playback analog content fine, but certain
> HD streams (again, playback) cause some prebuffering messages as the
> play starts up or when inserting onscreen menus or messages (eg. 'I'),
> and if I switch aspect ratios ('W'), playback (and frontend) hangs with
> incessant prebuffering messages.
>
> The issue seems bandwidth related. The streams for which I have problems
> have very high bitrates.  My confusion has been that the cpu isn't
> overly taxed, ticking along at perhaps 50% load.  XvMC, realtime, yadda
> yadda.

are you playing over a network?


> > If you can't do this then given the specs below, you are going to need
> > to allow the
> > devices in the video path more time on the bus to burst their data.
> >
> > It looks like the disk controller here has a latency of 0, I would up
> > this to at least 32.
> > I'm not very familiar with the ICH4, assuming it has a latency timer for
> > burst transfers:
> > (as root)
> > # setpci -s 00:1f.1 latency_timer=20
> >
> I tried setpci on my ide, but lspci didn't reflect any change in value.
> Nor any particular effect on performance anyway.

not all chipsets support the setpci command, my disk controllers stay
at 0 no matter what I do. I assume it ignores when I ask it to change
as opposed to not showing the actual value.


--
Steve