Newbie Question About CPU Power To Drive Display

[rdsherwood]

I just set up SageTV on a Dell 2.2 GHZ P4 with 768MB RAM, an Nvidia 6200 display card connected to a television through the svideo connector, and an HDHOMERUN to receive OTA DTV. It works OK for the most part, but when I'm watching live TV, the processor runs between 50% and 80%, leading to some sluggishness in operating the system. When I just have it recording (without watching the output), or if I watch it on another PC using Placeshifter, the CPU loafs along at 8% or so. So it appears that driving the display is eating up the CPU cycles. Is it normal to take this much CPU power to drive the display? Can someone give me some pointers on things to look at to improve the performance (i.e. to cut down the CPU power used to drive the display)? Or is this the reason that so many people seem to use a separate machine for the client?

I've looked at different options for Video Renderer (now on Default, Video Overlay and DirectX9 either caused choppiness, or didn't improve things), and the MPEG2 Video Filter (I'm using the SageTV Video Decoder, the default decoder increased CPU utilization to 80-90%). DXVA Hardware Acceleration is turned on, when I turned it off CPU utilization again went up. I tried different audio settings, but they didn't seem to affect things much.

I'm fairly ignorant about video processing (but am trying to learn). Any pointers and suggestions on how to reduce the CPU utilization driving the display would be greatly appreciated.

[Tiki]

Encoding and Decoding Video takes a lot of horsepower, and conventional x86 CPUs used in PC's are not optimized for these tasks (they are general-purpose: designed to be good at a wide range of tasks but not great at any one thing).

Anytime you must encode or decode using software, it is the CPU that is doing the heavy lifting. This is why it is best to offload these tasks to specialized hardware that is dedicated to video processing when possible.

The encoding of analog video is handled by your video capture device - make sure to get one that is capable of hardware encoding (such as Hauppauge PVR150, HVR1600, etc.). When recording digital video signals (Over The Air HDTV or QAM Cable signals) using devices such as the HDHomeRun or Hauppauge HVR1600, your PC does not need to do any encoding. This is because the signals have already been encoded by the broadcaster. Digital capture devices just grab the raw digital information being broadcast and just save it to a file on your PC for later playback.

This is why you can record video using a hardware encoder or one of these digital encoders with a very low-powered PC (Pentium III, 500MHz won't even break a sweat during recording). Playback of the video is another story.

When it comes time to playback the video, you must decode it somehow. Most current video cards have hardware acceleration for decoding MPEG-2 video. Some cards can also accelerate the decoding of other types of video. To take advantage of the hardware acceleration in your video card, the decoder you use must be written specifically for that purpose. Nvidia sells their own decoder called PureVideo that is written specifically to take advantage of the acceleration capabilities of their video cards. You may get better results using that decoder with your card. Besides CPU performance, there is a lot of variation in image quality depending on which decoder you use (of the decoders I have tried, the included decoder from Sage yielded the worst image quality, but YMMV).

One other thing to keep in mind is that even with a hardware accelerated video card, playback still tends to be more CPU-intensive than recording, particularly if you are playing back to a different format screen than the video was recorded at, since the image must be scaled and possibly interlaced or de-interlaced to match your display.

[Djc208]

Originally Posted by rdsherwood

I just set up SageTV on a Dell 2.2 GHZ P4 with 768MB RAM, an Nvidia 6200 display card connected to a television through the svideo connector, and an HDHOMERUN to receive OTA DTV. It works OK for the most part, but when I'm watching live TV, the processor runs between 50% and 80%, leading to some sluggishness in operating the system. When I just have it recording (without watching the output), or if I watch it on another PC using Placeshifter, the CPU loafs along at 8% or so.

This sounds about normal based on your setup. As Tiki said the MPEG2 decode requires all the HP, especially paired to an older low end card like your 6200. I would see similar numbers on my old 6200LE with my AMD Athlon. When I upgraded my gaming machine I moved the 7600 into the Sage machine and CPU usage dropped by about half. I use the nVidia decoder so the change is purely due to the improved hardware decode offered by the 7600.

Best bang for your buck would be to look for a newer low-end graphics card. For under $90 either of these cards should work well and are passively cooled for quieter operation.

http://www.newegg.com/Product/Produc...82E16814125039

http://www.newegg.com/Product/Produc...82E16814121064

But a better option would be:

http://www.newegg.com/Product/Produc...82E16814161210 or similar.

a little cheaper but slower: http://www.newegg.com/Product/Produc...82E16814102734

which also offer H.264/VC-1 acceleration in case you try to run an HD-PVR or HD-DVD/BD drive.

[rdsherwood]

Tiki & DeSoto, thank you very much for your detailed responses. They give me a much better understanding of what's going on.

DeSoto, the catch is, the PC doesn't have any AGP or PCI Express slots, so the card has to be PCI. That's what drove me to choosing the 6200 in the first place.

Nvidia offers PureVideo on a 30 day trial, so it looks like the first thing to try is to install their decoder to see if it takes better advantage of the Nvidia card's onboard processing, thereby lightening the load on the CPU.

My plan is to use this box pretty much exclusively with digital content (through the HDHOMERUN). So i'm not too worried about needing a lot of horsepower for encoding. The box has a big hard drive, and I set up a separate partition with 64K blocks for the mpeg files, and that side of things all seems to be working well. But if I decide that this box just doesn't have the horespower to drive the graphics, it seems like I have two options: 1) Replace it with a new PC that has enough power (and the better video card) to handle the graphics processing, or 2) use it only as a server, and buy a client front-end, such as the HD-100 Media Extender (assuming they can actually start supplying them) to drive the television. Just looking at hardware costs, it seems like #2 might be the better solution. Any opinions or suggestions on why this wouldn't be the best solution?

[CollinR]

PureVideo should fix you, it has support back to the MX4400.

Also if you are connecting via Svideo can you have the HDhomerun only pull in reasonably sized streams? Scaling 1080i to 480i is not helping your situation at all.

[paulbeers]

Originally Posted by rdsherwood

Tiki & DeSoto, thank you very much for your detailed responses. They give me a much better understanding of what's going on.

DeSoto, the catch is, the PC doesn't have any AGP or PCI Express slots, so the card has to be PCI. That's what drove me to choosing the 6200 in the first place.

Nvidia offers PureVideo on a 30 day trial, so it looks like the first thing to try is to install their decoder to see if it takes better advantage of the Nvidia card's onboard processing, thereby lightening the load on the CPU.

My plan is to use this box pretty much exclusively with digital content (through the HDHOMERUN). So i'm not too worried about needing a lot of horsepower for encoding. The box has a big hard drive, and I set up a separate partition with 64K blocks for the mpeg files, and that side of things all seems to be working well. But if I decide that this box just doesn't have the horespower to drive the graphics, it seems like I have two options: 1) Replace it with a new PC that has enough power (and the better video card) to handle the graphics processing, or 2) use it only as a server, and buy a client front-end, such as the HD-100 Media Extender (assuming they can actually start supplying them) to drive the television. Just looking at hardware costs, it seems like #2 might be the better solution. Any opinions or suggestions on why this wouldn't be the best solution?

STX-HD100 is the way to go unless you want Blu-Ray or DVD drive. As someone who fought long and hard with his full clients for years, the HD100 just works.

[Djc208]

Originally Posted by paulbeers

STX-HD100 is the way to go unless you want Blu-Ray or DVD drive. As someone who fought long and hard with his full clients for years, the HD100 just works.

And they're back in stock! (for now)

Sometimes it's sad how excited we get about this stuff

[rethdog]

I have 6800gs, my cpu usage is around 30% decoding and displaying a OTA HDTV signal, this is using the nvidia purevideo codec.

Also recently installing ffdshow for playing xvids (mpeg4), it seems to be pretty efficent using 30-40% displaying 720 x 380-ish movies.

I believe the ffdshow can also display mpeg2 streams so you may to try that before you buy the nvidia codec.

My processor is a XP2800 so in general purpose usage it's a bit more powerful than yours, although a P4 was more designed for this type processing, so you should get similiar results

check out a couple of post below on how to set filters, and check to see they are really being used!

[paulbeers]

Originally Posted by Djc208

And they're back in stock! (for now)

Sometimes it's sad how excited we get about this stuff

True dat!

[mikel]

I recall reading somewhere in the forum that PureVideo drivers are not available for Vista, and that Media Center in Vista already has PureVideo capability built-in for using the NVidia graphics cards.

I'm currently running XP with the evaluation versions of PureVideo, but I'm thinking of upgrading to Vista. I can get an upgrade Home Previum version for around $79. Any reason not to upgrade? If I don't have to purchase PV under vista, it like a $30 discount on top of that.

[rdsherwood]

So I installed Purevideo, and it appears to have helped some, with CPU utilization dropping around 5-10%. I haven't had a lot of time this week to tweak it, but the results are in the right direction.