[mythtv-users] hardware questions for HD to SD playback

[Jamie Stotz]

I'm getting ready to upgrade my backend / frontend box to something  
that can play back HD recordings.

My current board is an nForce2 running an Athlon at 1.8 GHz. It has  
onboard nVidia GeForce 4MX video, and I'm sending an interlaced  
640x480 signal out the VGA port, through a VGA to component converter,  
to a SD TV. My tuners are an PVR 250 and an HD HomeRun. I currently  
have to transcode and down-sample all my HD recordings to watch them.

I've read a bunch of posts here and elsewhere about the newer crop of  
nVidia cards that can do VDPAU but I have some questions about how  
that relates to SD TV. My main question is about how much and what  
kind of horsepower I need to play back HD recordings at SD resolution.  
I understand that I can use VDAPU to decode the recording, or, lacking  
a VDAPU capable card, I can use the main CPU if it's fast enough.  
However, that just gets me a decoded HD video. I still need to down- 
sample it to SD resolution and, if it is a 720P recording, I need to  
interlace it to feed my TV.

1. All the discussion about VDPAU talks about which DE-interlacers  
will work with which cards. What about interlacing? Is this process  
just as processor-intensive as de-interlacing? Is it handled by VDAPU  
or is it done by some other part of the card/driver? Is VDAPU even  
needed?

2. What about down-sampling? How much extra effort is that? Is it  
something that any card can do without a problem or is it something I  
need VDAPU or a fast CPU to do?

3. My current setup suffers from the bug in the nVidia driver that  
makes it only output 1/2 the interlaced fields. The picture is sharp  
and clear but only 1/2 the vertical res it should be. Has this been  
fixed yet? Does it effect the HD resolutions or just the SD ones? (Is  
1080i output as 720i)

Depending on the answers to the above questions, I'm thinking about  
getting a gigabyte GA-73PVM-S2H motherboard.

http://www.newegg.com/Product/Product.aspx?Item=N82E16813128072

This is an intel 775 socket board with an on-board nVidia 7100 GPU. I  
was thinking that with a Core 2 Duo CPU this might be fast enough to  
do what I want, and I could add a VDPAU capable card later, once myth . 
22 is out. The 7100 does not support Xvmc but with that CPU I figure  
it won't be a problem.

4. The choice of boards with Intel GPUs is much bigger than those with  
nVidia GPUs. I have seen the advice about nVidia GPUs working better  
with MythTV, but I was wondering if that is only of benefit if I'm  
actually using the GPU? If I get an add-in nVidia video card, such as  
a 9500, does it matter if the built-in GPU is from Intel? In other  
words, is the advice of using an nVidia GPU only for the GPU or does  
it apply to the rest of the chip set as well? Also, does it mean "get  
nVidia" or does it mean "don't get ATI or VIA" and Intel is OK.

5. If intel is OK, which one? They have so many. I've heard that some  
of the newer ones aren't well supported.

6. The aforementioned board, and ones like it, seem to be a few years  
old. They seem to all have DDR 2 800 memory and PCIe v1. Is this fast  
enough? Does VDPAU need faster RAM or PCIe v2?

7. This board doesn't have a serial port on the back but it does have  
a serial header on the board. Is this the same as a real serial port  
for the purpose of wiring up a serial IR blaster?

8. If I'm sending digital audio out the S/PDIF port to a receiver, do  
I care what audio chip is on the motherboard? Is that chip involved or  
is it just there to drive the analog outputs?

Thanks in advance,

Jamie

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