[mythtv-users] Trouble with HD playback

Sun Oct 31 02:16:43 UTC 2004

On Friday 29 October 2004 20:53, John Goerzen wrote:
> On Fri, Oct 29, 2004 at 10:47:47AM -0700, Jarod Wilson wrote:
> > On Friday 29 October 2004 07:02, John Goerzen wrote:
>
> Thanks for the detailed and helpful reply, Jarod.  Let me try to give
> some more info...

Cool, no problem.

> > Sounds very similar to what I saw with ALSA 1.0.6a. Backing off to 1.0.5a
> > and enabling aggressive sound card buffering fixed all my audio problems.
> >
> > > I thought at first that the problem could be an underpowered CPU.
> >
> > I still think that's the problem, after seeing that you're running an
> > Athlon XP 2200 and a Radeon. Which brings other issues to mind (I'll get
> > to that at the end)...
>
> Could be right...

Someone else is getting okay playback on much slower box using XvMC on a GF FX 
5200...

> > > Configuration:
> > > MythTV 0.16
> > > Athlon XP 2200+ 1.8GHz
> >
> > Definitely under-powered.

For software-only decode.

> I tried mplayer, which seems to confirm that.  I haven't yet researched
> what else this motherboard can take, but assuming it could take a fast
> enough Socket A CPU, do you have a suggestion?

Something with 512K cache, and hopefully, a 400MHz FSB, if you can get that 
fast. I went as fast as I could in an Athlon XP w/my 3200.

> > > 256MB RAM, 100MB free
> >
> > Not sure if 256 is sub-optimal for HD, I've got 512.
>
> I've got plenty of RAM free, so I'm pretty sure that's not the issue.

Okay, I didn't think that should be a problem.

> > > ATI Radeon 9200 video card
> >
> > Ick. My Radeon 9000 had multiple issues playing back HD content. But they
> > differed depending on the driver used... Switching to an nVidia card
> > immediately cured all those problems. However, its been a while, maybe
> > the fglrx driver sucks a little less wrt HD playback now... :-)
>
> My motherboard has some sort of on-board nvidia stuff.

GeForce 4 MX-class, most likely.

> I stopped using 
> it because the ATI card had a DVI out port, which I briefly experimented
> with using to drive the TV.  When I stopped, it was all set up for the
> ATI, and the ATI seemed to work better and a little faster, so I kept
> it.  Plus it freed up some system RAM (the onboard stuff uses system RAM
> for the framebuffer -- that's icky too.)

Yeah, I went to an AGP card myself. Using the onboard video also limits your 
memory speed (can't run dual-channel DDR-400 mode when using onboard 
graphics, max is single-channel DDR-333). The FX 5200 also seems to handle HD 
content a bit smoother than a 4 MX.

> The fglrx driver has done quite a good job for me.

I'll have to revisit that with my new laptop...

> > >   XFree86 4.3.0
> > >   ATI fglrx 3.14.1 driver
> > >   Originally was using 640x480 resolution.  Also tried 800x600.  No
> > >   difference.  24bpp.  Xv enabled, Xvmc disabled (I think -- I have no
> > >     idea how to turn Xvmc on or off)
> >
> > Ouch, you're tacking some serious scaling on top of trying to decode.
> > Sounds like you're outputting through SVideo.
>
> Yes, I have had trouble making 960x540p work correctly through the
> SVideo out port.  A proper VGA-to-component adapter is on the list but
> not purchased yet :-)

SVideo is physically unable to display anything greater than NTSC or PAL spec. 
Even when you're using 1024x768 out the TVOut, its getting scaled to 720x480 
(or 720x576) by the TVOut chip. SVideo doesn't have the bandwidth for HDTV 
resolutions.

> It was my impression that with Xv support in hardware, scaling was done
> in hardware (by the video card), and thus not an issue... am I mistaken
> there?

Xv helps, but a ton is still done in hardware. XvMC does a whole lot more in 
hardware, but doesn't look as good (and places other limitations on what you 
can do w/your output in Myth). However, judging from the guy who is able to 
play back those HD clips on a 1.4GHz Celery w/a GF FX 5200 and XvMC, it does 
help out a ton, so you might try that w/your onboard graphics...

> > > Debian sid
> > > Sound using ALSA, AC97 onboard
> >
> > Native ALSA output, or OSS emu output? My audio experience improved a bit
> > when I started outputting raw AC3 to my amp.
>
> Native ALSA, but not AC3.  My system does have both coax and optical
> digital out, but I haven't played with them yet.

Offloading AC3 decode to an amp also helps to lower cpu load a little bit. And 
produces superior sound (at least that's the case w/my Yamaha amp).

> > > Let me know if there's any other information I can provide.
> >
> > Why you're not getting any video at all, I don't know, but you're
> > definitely short on processing power. How do those files look when played
> > back with mplayer?
>
> That was an interesting test.  I tried the ABC file.  It played
> *beautifully* for the first 10 seconds or so.  Perfect video and sound.
> Then after 10 seconds, the sound dropped out -- video continued.
> mplayer displayed a message saying my system was way too slow, CPU
> utilization was indeed 99%, and yet the video continued playing until
> what I assume was the natural end of the clip.

I think it was less than a minute long.

> I have no idea how it managed that if my system was way too slow.  Or
> with 99% CPU utilization for that matter.

Dunno...

> While we're on the topic, are HD streams really such a higher bitrate
> than DVDs?

Yes, they're a considerably higher bitrate.

> This machine has no trouble at all playing DVDs.  I know the 
> resolution is somewhat higher, but that just seems extreme...

DVDs are 720x480, HDTV (in its two best forms) is 1280x720 or 1920x1080. That 
ABC clip is 1280x720, the CBS clip is 1920x1080.

> Thanks again.

You're welcome. :-)

-- 
Jarod C. Wilson, RHCE
jcw at wilsonet.com

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