[mythtv-users] Questions: multiple HD tuner backend with Pentium 4 3.0 GHz front-end

[Marland V. Pittman]

I used to have a TiVo and liked it. Then we got DirecTV to get multiple 
tuners, then we got a DirecTV HD box, and finally we got an HDTV to 
watch it on. Then we decided that's too much money.... we got rid of all 
the stuff, but we still have the HDTV. I snagged an indoor powered 
antenna from a buddy and hooked it up to our SDTV downstairs, and found 
the signals to be semi-adequate.

One day, I get the bright idea to hook the antenna to our HDTV, 
upstairs, in the master bedroom, and discovered what I was missing. OTA 
HD is fabulous, and free. So, now we want to use the bathroom on our own 
schedule again, and record Teletubbies for the kids. I'm thinking about 
building a MythTV system with some hardware I've got:

- I have no tuners, but I'm thinking about using the Avermedia A180 or 
the PCHDTV 5500.
- I have a few socket 478 CPUs that I can throw at the project, but the 
top three are a P4 3.0 GHz, P4 3.0E GHz, and a 2.8 GHz.
- I got a couple of open box socket 478 motherboards from NewEgg that 
have via chipsets, take DDR2 and PCIe, and grabbed 4 1 GB sticks of DDR2 
as well.
- I have three sticks of DDR400/PC3200 512 MB and three sticks of DDR 
266/PC2100 512 MB (I think... they could be DDR333/2700)
- I snagged a Biostar motherboard with 5 PCI slots and 1 AGP slot from 
Geeks.com, it has onboard graphics and an Intel chipset.
- I have two PCIe NVIDIA 6600 video cards They have 256 MB of RAM, 
rather than the standard 128 (which gives me fits in Fedora because I 
have to install in VESA mode - the nv driver goes bonkers on them... the 
binary driver from NVIDIA works great though.) I've got VGA, component 
TV-out cables, and DVI outputs for those.
- I thought about getting low-profile cases for the front-ends and going 
with a 8400 GS in each machine. I read that they assist in HD playback, 
and I can get a low-profile bracket. My 6600s are not low-profile.

I'm still deciding on cases and such for the whole set-top experience, 
but right now, I'll probably be running them open air on a table to test 
things out until I scrape up some cash to put machines in nice cases. I 
have a couple of Vista MCE remotes and MCE keyboards, which I hope I can 
program to work with Myth TV.

So, I figure, HD doesn't take a lot of CPU to record, but lots to 
playback, and I could use a Pentium 4 2.8 GHz machine with multiple HD 
tuners as a backend. Then, I could put the two 3.0 GHz machines to work 
as frontends for HD playback. I know we only have one HD Television, but 
I've got lots of CRT monitors, and the Standard Definition TV downstairs 
will get upgraded some day.

I'm thinking I can use a small hard drive, or a network boot on the 
front ends, and just load up the backend with huge drives. I've got some 
4 GB drives that'll probably die on me if I use them, prompting me to 
find a diskless/network boot solution... I'm probably going to use 
Fedora, as I'm familiar with it. I'm by no means an expert, but I use it 
occasionally at home. I installed Fedora 8 RC3 yesterday, but rather 
than try to build Myth TV on F8, I may just go with MythDora.

I don't know if I'll just buy 5 tuners at once, or try to incrementally 
upgrade. I'm thinking it's a relatively expensive purchase at once, but 
it'd be much more impressive if I can record two shows at once, and 
watch two other shows on each TV.

So, it looks like this:

backend: P4 2.8 GHz, 512 MB / 1 GB RAM, 5 tuners, onboard graphics (or 
an AGP card if I need it)
frontend: P4 3.0 GHz, 2 GB RAM, NVIDIA 6600 256MB
frontend: P4 3.0 GHz, 2 GB RAM,  NVIDIA 6600 256MB

Questions:

- A P4 3.0 GHz machine (with XvMC) on a 6600 or an 8400 GS should work 
for HD playback, right?
- Does the 8400GS HD playback assistance only work in Windows?
- Do I really need 2 GB of RAM in a front-end? Will 1 GB be fine?
- Is 2.8 GHz fast enough to simultaneously record 3 or more HD streams? 
I remember reading that you could record with very little CPU power, and 
that playback was the big issue.
- Does my backend need lots of RAM (more than 1 GB) to record from 
multiple tuners?
- Does separating the frontend from the backend only help playback? 
Would I benefit from having the Tuner in a frontend machine as opposed 
to the backend? It'd be nice to just have one antenna split into 5 cards 
at one location, rather than wiring up the whole house.
- I read mythtv hates VIA chipsets. Should I just quit while I'm ahead 
with the front-end machines and get new motherboards?
- I assume HD needs lots of bandwidth. Do I need to upgrade from a 100 
megabit switch to gigabit to pull this off? I'm hoping if I have 5 
tuners in the machine, but I'm only pulling two tuners worth of live 
content, or two prerecorded shows at once, I can manage.
- A180 vs PCHDTV 5500. The A180 is cheaper, but the PCHDTV 5500 is 
supposedly made for Linux. I want easy, and I'll pay for it, but if the 
A180 isn't any easier to use/install than the 5500, I'll take the 50 % 
savings x 5. Is that broadcast flag thing still an issue?
- Is MythDora being based on F6 really a problem? I mean, these are 
going to be appliances... I'm not planning on mucking about with them, 
but I would like to be able to upgrade them as necessary.

Sorry for the long post, but thanks in advance for any insights.