[mythtv-users] HDTV playback specs?

Joe Votour joevph at yahoo.com
Sat Sep 2 23:04:28 UTC 2006

> I've just upgraded to an HDTV DCT6200 cable box from my cable company.
> Using firewire and MythTV's built in DCT6200 support I'm able to
> watch/record all my HDTV channels, premium (HBO/Showtime/Etc) and
> otherwise, as well as all the regular SD and digital channels.  The
> problem.. while HDTV playback is *almost* smooth it still shudders, gets
> out of sync with audio, and sometimes there is that "snowy" pixel
> effect.  It not that bag, but even a little makes things annoying.  Here
> are my system specs:
> AMD 64 2000+
> 1GB PC2100
> DFI nForce 2 based motherboard
> NVidia FX5200 /w 128MB (AGP)
> Generic firewire card (NEC chipset)
> Onboard gigabit NIC - (100Mb connected but could be 1Gb, don't see a
> point since SD recording only used 5Mb/s per tuner, even if HDTV is 10x
> that... ???)
> 80GB ATA/133 drive (all recording on a NFS 4 network share.)
> All this system does is MythTV.
> Watching HDTV my CPU usage runs anywhere from 35% to 85%.  The norm is
> ~75%.  Memory and disk i/o is almost nill.  This is with XvMC enabled,
> Bob2x deinterlacing, frontend running with root privileges.   I've also
> set the nvidia options in xorg.conf :
> Option "RenderAccel" "1"
> Option "NVAGP" "1"
> Option "XvmcUsesTextures" "false"
> Recording HDTV /w out playback I see 3% CPU usage.  Watching HDTV from
> my much faster master backend is flawless.
> So given all this what has been people's experience?  Can I get
> completely smooth playback with these specs somehow?  An option I am
> missing etc?   If not what's the most worthwhile  part to upgrade?
> I have a couple ideas:
> 1. Replace my FX5200 /w a fanless 6200 with 256MB ~$50 (enough of an
> upgrade?)
> 2. Replace with a fast Socket A CPU ~$100 (enough?)
> 3. Both 1 and 2
> 4. Use a first gen Nforce 4 board I have laying around (Socket 939)  and
> buy an ~ AMD 64 3200+, 1-2GB PC3200 DDR.. all new PCIe 6200 - ~$$$
> I'd prefer not spend all that much since all I want is a MythTV frontend.
> Suggestions?

You'll find lots of debate on this.

I have a frontend-only system that I use for HD playback, using shows
recorded via a DViCO FusionHDTV 5 Lite connected to a UHF antenna.  This
system is an Athlon 64 3200+ (Socket 754) with 512MB of DDR400 RAM, and I
stream the shows over a 100Mbps connection.  Using XvMC and Bob, I can
play my HD content with very few stutters with a CPU utilization of about
80% max.  If I do something with the OSD, then it sometimes stutters.

With the recent drop in prices, I'm looking at getting a 4400+ AM2 to
replace it, and making my frontend the server (at the moment, the server
is a XP 2400+).

Unfortunately, playing back HD streams is rather CPU intensive because
it's all done in software, unless you use XvMC, which offloads some of the
work to the video card.  Most set-top boxes are able to use miniscule CPUs
(like 200MHz) to play back HD content because they have integrated MPEG-2
decoders that do all of the decoding work - unfortunately, as MythTV
users, we don't have that luxury.  Your current frontend (and mine) would
playback HD streams perfectly under Windows though, as I've done it.

-- Joe

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