I had a successful R5C7 setup running with a PVR350 (but output to TV on a 64Mb Nvidia card 'TV out') The computer's an IBM with a 1.8 ghz P4 processor. Completely adequate for NTSC TV.

So in the spirit of exploring the digital spectrum, I added an Air2PC card.

My findings have been thus:

I get a lot of DTV stations in my area. I use an attic antenna with a head end amplifier, and distribution amplifiers in the house (UHF loses strength rapidly in cable..) [Myth is indicating 100% strength on most stations]

The above setup is capable of playing SD digital 'live' TV, & probably some of the lower 'stream flow' HDs

Not surprisingly, 'live' HDTV from the major networks (1080 & 720) hitches the sound and picture as the amount of data overwhelms the slow processor.

What i have found, is that these large HD recorded files (7.4 gig/hr) Will play fine in Xine, as long as the backend isn't commercial flagging, so Xine has nearly full use of the processor. The files hitch when played by Myth's frontend.

So I guess my question is- what is different between Xine & Myth that makes the difference in one playing without hitching and the other not, due to a slow processor ? Decoding algorythms ? Software overhead ?

(I'm looking on e-bay for a cheap (!?) 3.6ghz machine... )

Snaproll, there's a lot written on this topic, so it's worth searching the forum to see what other's have found. Having said that, here are some quick tops:

1. Playing back with libmpeg2 typically reduces CPU utilization.

2. De-interlacing is expensive. There are multiple methods available in the front end. From least-expensive to most-expensive they include linearblend, kerneldeint, bob2x.

3. Some Nvidia cards support XVMC. XVMC can offload a lot of the playback processing from the main CPU to the graphics card. I use an nvidia-based e-geforce FX6200 with XVMC and playback of 1080i, deinterlaced using bob2x utilizes ~35% of one of my two CPU cores. Each core is 3.0ghz.

There are mixed results with XVMC -- works great for some, not at all for others.

I am running R5A30.2 with Nvidia driver 8756. Good luck!

Marc

Snaproll, there's a lot written on this topic, so it's worth searching the forum to see what other's have found. Having said that, here are some quick tops:

I have read 3 pages back on the 'digital', 'hardware', and 'general' forums.



1. Playing back with libmpeg2 typically reduces CPU utilization.

Tried it. For my setup 'as installed' was best.



2. De-interlacing is expensive. There are multiple methods available in the front end. From least-expensive to most-expensive they include linearblend, kerneldeint, bob2x.

I stuck with linearblend, not having the horsepower to spare on more processor intensive processes.
Tried the Hard Drive speedup too, but DMA was already enabled and the other settings were a spit in the ocean as far as getting any additional drive speed.


3. Some Nvidia cards support XVMC. XVMC can offload a lot of the playback processing from the main CPU to the graphics card. I use an nvidia-based e-geforce FX6200 with XVMC and playback of 1080i, deinterlaced using bob2x utilizes ~35% of one of my two CPU cores.

Tried all the options... Each had warts that made them not as desirable as the default, running on my equipment...

Is there any rule of thumb as to how much video card is necessary and how much is overkill ? I HAVE 64mb MX-400s, I note many run 256 mb 5200's


Each core is 3.0ghz.

See note about seeking faster equipment....

Did you check your playback output to see that xvmc is actually being used when you enable it? I'm pretty sure that MX 400s are GeForce 2's, and so do not support any xvmc acceleration, which requires a geforce 4 or higher.

5200s are the most popular mostly because they're the most bang for the buck. They're the fastest cards which can come without a noisy fan, they support xvmc somewhat better than the 6xxx or higher series cards (if you want things like the experimental color OSD), they can have DVI and tv-out, and the 3d performace isn't that bad if you need that sort of thing. I think 256mb of video ram is overkill, but according to the mythtv wiki, 128 mb is needed to process HD streams, no matter what playback method you're using, so I think the playback of these streams might actually be too much for your video card.

Did you check your playback output to see that xvmc is actually being used when you enable it? I'm pretty sure that MX 400s are GeForce 2's, and so do not support any xvmc acceleration, which requires a geforce 4 or higher.

Yes, I got black & white menus & somewhat degraded picture using XVMC, so I changed back. Whether I need more video card is still under consideration, it may well be, that the MX-400s don't provide all the support necessary to unload the processor, I initially bought them to provide the 'TV out' jack.


5200s are the most popular mostly because they're the most bang for the buck. They're the fastest cards which can come without a noisy fan, they support xvmc somewhat better than the 6xxx or higher series cards (if you want things like the experimental color OSD), they can have DVI and tv-out, and the 3d performace isn't that bad if you need that sort of thing. I think 256mb of video ram is overkill, but according to the mythtv wiki, 128 mb is needed to process HD streams, no matter what playback method you're using, so I think the playback of these streams might actually be too much for your video card.

Thanks, misterflibble,

Therein was the kind of 'education' I was seeking, and suggests it would be worthwhile to aquire a MX-5200 for further experimenting.
'stream too much for the (MX-440) video card' probably not a factor because Xine will play an HD stream all right (with the occasional dropping of frames on fast motion. I think the hitching under Myth frontend is due to the processor pegging, but I think I'd like to see if the frame-dropping under Xine is improved by a better (MX-5200) video card.

Hey snaproll,

I have an athlon xp 2500 and a nvidia fx 5200 working with an ATI hdtv wonder.

My system sounds fairly close to yours, maybe a bit faster. I have some trouble keeping everything smooth when my color depth is set to over 16 bits even though my CPU isn't at 100%.

How much disk throughput do you need to intercept an HD signal? I've read elsewhere that it's around 19-20 MB/s (The video stream out of the tuner was MPEG2). Does myth just dump it out on the disk raw?

Does myth send the signal to the video card during/after/before it hits the disk?

I'd like to know if I'd have a performance gain or penalty by switching to mythtv - the ati software that comes with hdtv wonder pretty much sucks.

Dan

have an athlon xp 2500 and a nvidia fx 5200 working with an ATI hdtv wonder.

My system sounds fairly close to yours, maybe a bit faster. I have some trouble keeping everything smooth when my color depth is set to over 16 bits even though my CPU isn't at 100%.

My understanding of Athlons is 2500 means 'equal to a 2.5 ghz Pentium' even if it doesn't crank 2.5 ghz... Still kinda on the edge if it performing other tasks at the same time. My understanding is that HD requires 3ghz or better for proper performance.



How much disk throughput do you need to intercept an HD signal? I've read elsewhere that it's around 19-20 MB/s (The video stream out of the tuner was MPEG2).

I think I've seen that figure too. Using 'hdparm' to check the disk capability I got:

root@mythtv:~# hdparm -tT /dev/hda

/dev/hda:
Timing cached reads: 916 MB in 2.01 seconds = 456.47 MB/sec
Timing buffered disk reads: 156 MB in 3.01 seconds = 51.78 MB/sec

So the disk shouldn't be a bottleneck with DMA on.



Does myth just dump it out on the disk raw?

Does myth send the signal to the video card during/after/before it hits the disk?


records it first, then plays it back.



I'd like to know if I'd have a performance gain or penalty by switching to mythtv - the ati software that comes with hdtv wonder pretty much sucks.

No experience with the ATI product.

Well as far as the ATI product goes - they are introducing a new chip called the 650 theater pro.

I'm not sure that will help at all, being an ATI product. I understand they don't have outstanding opensource support.

Dan

Just for the record, the HDTV stream is around 20M BITS/sec, not bytes/sec. Pretty much any disk drive better than a floppy should be able to keep up with it, especially for only one channel. It gets a little more stressful if you're recording three HD streams simultaneously.

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