I've been running myth since R5C7. Since that time, I've always had this sort of occasionally skippy HDTV issue. Here's my hardware setup and a few interesting data points:

Nforce2 motherboard (gigabyte 7NF-RZ)
Athlon XP 2200+
Nvidia 6200 AGP (128MB ram on board)
Chaintech audio (Can't remember the model number offhand- its what was in the dragon)
512MB ram
300GB ultra ATA WD
PVR-150 - the one without the remote
HD5500

I finally did some experimenting last night so I've got some data to present.

All my issues are related to watching live HDTV (and recorded HDTV to a lesser extent). Basically, with XvMC enabled I'm running at about 43% CPU usage - almost all of it is mythfrontend, and a little bit of swap is used (48k or so), and the picture stutters about every 30 seconds, sometimes badly. I get about 100 'NVP: prebuffering pause' messages in the frontend log per second. While running 'top' I see the cpu useage spike when these pauses occur, but I'm not really sure where the peak is (I did see an rrd process or two pop in there at least once but not every time.)
If I turn XvMC off (instead using libffmpeg), recorded HDTV works great. Watching live HDTV works pretty well too, but I get the occasional skip or pop (not nearly as bad as with XvMC). The cpu runs at 92 - 93%- again all mythfrontend, not leaving much room for anything else. I didn't try recording off of the SD tuner while watching liveTV, but I'm not expecting great results from that.

Basically, I know that I need more processor in order to NOT run XvMC successfully all the time. Last night's testing showed me that throwing more hardware at this problem would fix it, and I'm pretty much OK with that. But I'm curious- why am I having XvMC problems? I should specify that the HD channel I was watching had a signal strength of 92%, broadcast in 1080i, but downscaled and output DVI to a 480p widescreen projector. The broadcasted format doesn't seem to make much of a difference though, as the 720p stations act the same way.

The only thing I can do for free here is throw more ram in the box- I think I have some laying around. But what interests me is why would this fix the issue?

Does anybody have any other ideas?

I doubt more RAM would do anything for you. I hate XvMC so I haven't played around with it much. I went the root of beefing up my frontend box (1GB RAM, X2 3800+, ASUS M2NPV-VM). CPU prices are pretty low these days: you can get a dual-core AMD processor for less than $100. Of course then you'd need a new motherboard, and probably new RAM because it'd be DDR2...

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LinHES 8.3, 1 BE, 3 FE

I'm thinking the same thing about the ram. Based on the various postings I've read, Nvidia XvMC is having a bit of an issue in this driver revision. Some people are having great luck with it though, so it seems there's a conflict with something uncharacterized (hardware? software?).

Its a socket A board, so my ideal solution would be to pop an Athlon XP 3000+ or 3200+ in there. I wouldn't even have to reinstall. If the bottleneck is CPU only, the 3200+ should yield a 45% increase in performance and my cpu load would drop back to around 55%.

Now, I know its not CPU only, but the FSB speeds are faster as well. I just wish I knew what the XvMC issue was.

Upgrade to R5f27,

One of my frontends is a athlon 2400, I had skipping issues in the past with hd and XvMC when the menus where up but the latest version of knoppmyth made HD playback on that system with XvMC turned on work well. I only see the slight skipping during the osd fading and could eliminate that by turning off the fading if I wanted to but, it's not bad enough to bother.


If you don't want to upgrade then you may want to look at you sync to vblank options in the nvidia application.(right click desktop and look for an application called nvidia)

Just to be sure, with XvMC enabled do you have a color or BW OSD? If its color, and the recording is raw (i.e., not transcoded), then XvMC is not working.

I'm surprised you get decent HD playback without it. I can't, and I'm running an Athlon 64 3200, 1gb ram.

Thank you all for the help and suggestions. Please keep it coming!

mogator88- The OSD is B&W with XvMC enabled, color without. Good sanity check though. Seems like I double checked a log at some point to verify that XvMC was running as well. It may be that my output device is 848x480, X.org is natively set to this, and therefore I have a lot less pixels to keep track of and software rendering can almost keep up. I've also done some tweaking to xorg.conf, and the setup->tv->playback options in mythfrontend as the default options cause wicked pausing wihtout XvMC at first. If you'd like specifics of what I have set I'll be happy to provide them, but its basically no XvMC, onefield deinterlacing, and the only thing checked besides that is extra audio buffering.

datobin1- I am, in fact, running R5F27 now, on a fresh install ever since zap2it disappeared (I'm now on Schedulesdirect). I previously ran R5D1, and before that R5C7. This issue always existed, but its definitely little worse now than previously (sorry I can't be more empirical).

When XvMC is enabled, the skipping during the OSD fade is really bad, and occurs about once in every 30 seconds afterwards, sometimes immediately recovering, sometimes taking several seconds.

As you noted in the thread I started, your problem sounds a lot
like mine. With XVMC I get smooth playback with 50-60% CPU
usage with occasional bursts of "NVP: prebuffering" messages.
When they happen, they happen in bursts at 1 second intervals.
What triggers them on my machine is the OSD.

Without the OSD, I sometimes see smooth playback with no
messages for 20-30 minutes at a time.

The only answer I can come up with is that my 66MHZ PCI slot is
just too slow. Somebody else reported that 2X AGP and an
FX5200 just wouldn't work for him, but an FX5200 (same board?)
in a faster AGP slot did work. My 66MHz PCI slot is
approximately equivalent to 1X AGP, which is pretty slow by
modern standards.

So, my question is what speed is the AGP slot?

I don't think I found any reports of HD playback working for
anybody running anything slower than 4X AGP. I swear somebody
reported success with HD playback with a PCI card. But, I don't
know what video board was being used and can't find the posting
(the forum search is bloody useless).

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Grant

I wouldn't recommend that route. I think you would just be frustrated. That cpu might still not be enough to run HD. (I'm not positive, perhaps someone else has tried it?). I think you should be going for a dual core processor. Not only that, but you'll probably pay more for that old processor than a new one. Go ahead and price them out. You've passed the point where the stores are having clearances on the processors and now they are in high demand from people like you who have a motherboard and just want to upgrade their processor.

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LinHES 8.3, 1 BE, 3 FE

According to

http://www.gigabyte.com.tw/Products/Mot ... uctID=1819

it's a 4X/8X slot. I think that should be plenty, so no help there.

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Grant

grante-

yep- 8x on the nvidia 6200. I have a whole lot more prebuffer pause messages though- on the order of 100 per second. I'll start poking through some mythtv forums to see if I can figure out what that message means.

kmkittre-

This is some really good advice. The best deal by far I can find on socket A is off of ebay, and they're not old enough to drop below $60 yet.
On the other hand, I've got PRETTY good HDTV live play (remember my output is 848x480) on the 2200+ just using software, as long as I'm not trying to record an SDTV show at the same time. Based on the peak loads, the 3000+ would make it seamless for everything I want to do. This would suffice until I upgrade the projector to a higher resolution (which is about least 2 years off). At that point, the HDTV would stutter again, but then I can replace this machine (the one I'm typing on) and send it off to be the new mythfrontend.

Mogator88- can you help me confirm a theory? What resolution are you running? I'm thinking that my lower output resolution lets me get away with HD software playback on the weaker machine.


But I can avoid any purchases if the XvMC will work properly. Anybody have an idea why it doesn't?

Thank you all for the feedback, this has been most helpful so far.

I'm running 1366x768. That is a lot more pixels to drive....

It certainly is. It also tells us something that I was not aware of until yesterday. I always thought the stream was decoded at its full resolution and then scaled to fit your output device, but that would mean no performance increase at lower resolutions.

It isn't? That's really surprising. I don't see how you can
decode at a resolution other than that at which it was encoded,
but my grasp of MPEG2 encoding is a bit vague.

If displaying at lower resolutions helped, you'd think my
system with a 3GHz P4, an FX5200 with XvMC driving a 640x480
display would be able to keep up, but it can't.

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Grant

I'm only saying that based on my testing- I didn't poke through the code or the mpeg2 standard to determine it. Also- looking at other posts, people have noticed a performance increase when they accidently scale 30% of the picture off of the screen, only displaying the left 70%.

grante- I think that at 640x480 on a 3GHz P4 you should be able to display HD without XvMC, which is where I'd like to be. Have you given that a shot? Also, your xorg.conf will have to be set to 640x480 so its all native.

Good point (that was me with the 70% picture -- but you
probably knew that). I suppose It could also be that the
reduction in CPU usage is due to XVMC not using textures.

Yes, I get 100% CPU usage with constant stuttering (video and
audio).

It is.

I'm not really sure what you mean "native", but the X server is
running with a root window size of 640x480 pixels.

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Grant