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PostPosted: Sun Dec 30, 2007 6:24 pm 
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Joined: Sun Dec 30, 2007 5:20 pm
Posts: 19
This is a rambling post for no particular reason. It's just my first attempts at making an HDTV recorder using KnoppMyth.

I am US-based and receive broadcast ATSC. I have a 720p Samsung DLP display with component, VGA, DVI and HDMI inputs.

I bought an HD-3000 back before the broadcast flag was overturned to make sure I had had a freely usable HD tuner card. I didn't get around to trying it until this past week. I now want to build a dedicated HD PVR. I had almost talked myself into buying an HD TiVo but realized I'd get more recording time for probably less money if I build my own HD PVR.

So as a test I cobbled together parts I had lying around:
- the pcHDTV HD-3000
- Pentium III 1 GHz cpu (133 MHz FSB)
- 192 MB PC133 RAM
- GeForce 5200 FX AGP (running at 4x on my mb) using VGA out
- UDMA/66 or UDMA/100 hard drive
- ISA (!) Sound Blaster card
- random network card and DVD drive

I did an auto install with the KnoppMyth R5F27 CD.

To my delight I was able to record ATSC streams and then play them over the network (after enabling Samba) on my Windows box. Myth even tried to play the streams, but of course this system isn't powerful enough to make it watchable. Linux didn't load the driver for the sound card, but it wasn't worth troubleshooting since this was a test setup. X was running in 800x600 mode; once I got it into 720p but couldn't duplicate it.

Next I took apart one of my Windows lab servers and created a new frankenstein MythTV box with:

- Althon XP 1800+ cpu (133 MHz FSB)
- 512 MB PC133 RAM
- on board audio, probably AC97

I didn't reinstall; I just moved the hard drive over. The audio drivers loaded and worked automatically. Playback of HDTV streams was stop-and-go; not watchable for entertainment but recognizable. Then I discovered I wasn't using the nvidia drivers (or XvMC) for X. I made a couple of changes to the config file based on the Myth and KnoppMyth docs and enabled XvMC.

To my surprise I can actually watch live HDTV with this Athlon XP 1800+ and XvMC. Barely. Whenever something goes on in the background or I trigger an on-screen display the playback suffers. And I may be watching 720p streams; I'm not sure if I've tested 1080i sufficiently to say it's viewable.

I am now wondering if I can make a usable system with the PIII 1GHz as the backend and the Athlon XP 1800+ as the frontend. I doubt the frontend will be able to deal with on-screen display, but it may be able to play HD well enough if that's all it's doing. I'm not sure if I'll be happy with this, but the cost will be $0 plus a bigger hard drive.

If I buy new parts I'll need a motherboard, cpu and ram. And if I get a mb without an AGP slot I'll need integrated video or a PCI-x video card.

My dilemma is how powerful to go and/or how much I want to spend. These seem to be my choices:
- try to make my free "frankenstein" (old parts) system work
- buy parts just powerful enough to make HDTV play smoothly
- buy parts that are easily upgradeable for HD-DVD / Blu-Ray playback
- buy parts that can handle HD-DVD / Blue-Ray decoding now

Getting parts that were upgradeable for Blu-Ray sounded like a good idea at first, but the E6000's are 1066 or 1333 FSB and the matching RAM is more expensive. So I'm thinking I'll tinker with the Athlon XP 1800+ as a dedicated frontend, and if I can't make that work well enough for HDTV then I'll aim for something just over 3GHz/3000+.

I'm surprised the PC133 RAM seems to be adequate for HD playback on a combined box. It's not even DDR. So I don't expect to have to worry about RAM bandwidth until I try to get HD-DVD or Blu-Ray to work.

UPDATE 1: Now that I have a few recordings and am trying to watch some shows as I would normally (instead of just testing) I'm seeing how weak this Athlon 1800 / 5200FX sytem is. If anything is going on in the background the playback suffers--often badly. When commercial flagging is happening--even though it's low priority--playback is unwatchable. Right now nothing is recording and there are no jobs running, but periodically I'll hear the hard drive do something (probably a mysql action). This is not using much cpu directly, but there was a lot of cpu i/o wait which caused playback stuttering during the activity. I'll update again after I get the backend and frontend separated onto two machines. As it is, an Athlon 1800+ XP with GeForce 5200 FX w/ XvMC isn't quite satisfactory for daily HDTV watching, but that's about what I expected from reading about MythTV before I started this.

UPDATE 2: The Athlon XP 1800+-as-a-frontend test may not get done. Fry's had a sale today and I bought a Core 2 Duo E6750 (and mb/ram/etc) and plan to use it as a combined MythTV box. I'm not sure making the Althon 1800+ a standalone frontend would have worked because these cheap network cards take up cpu cycles unlike a DMA hard drive controller, so it may not have been able to handle the network reads and HD decoding even with XvMC. In fact I'm pretty sure it would not have worked satisfactorily. ... Anybody know where I can freely and legally (in the US) download some 1080p video for HD-DVD/Blu-Ray decode testing on my new C2D?


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