MythTV

I started trying to install and use MythTV with HDTV in early December, 2004. The PVR part was working by Christmas, and we have been enjoying it since. But the HDTV, using the HD3000 card from PCTV, did not work cleanly until today (2 Feb 2006). In order to save $1000 in HD-Tivo costs, plus ongoing service charges, I spent innumerable nights and weekends fighting (and learning about) Fedora Linux and the HDTV drivers and configuration.

Answers

Here are the answers to questions that I could have used 14 months ago:

A 1.7 GHz CPU runs at 20% utilization on regular TV show playback. The secret is in the video card: the NVidia 5500 makes the difference, and probably worth the pain of their drivers.

The early drivers for the HD-3000 card were a little broken. But that was a while ago. They work fine now.

The data-rate defects in HDTV processing are caused by defect chips/chip design of something on the motherboard, probably the Via chips. It does matter which motherboard you buy to support MythTV, and not all Taiwanese motherboards will do. The MSI board works fine, and so probably does any board built by Intel and maybe Dell. Steve Bellovin adds:

NOTE: Motherboards with the Via chipset are notoriously bad with DMA and have caused numerous issues with ivtv, including hard locks. See the ivtv website http://ivtvdriver.org for the latest information on what works and what doesn't.

Moving the capture to a backend machine helped resolve these diagnosis issues. While watching HDTV, the backend (2400 MHz Pentium 4) runs at 2% CPU usage, which means that I can use a cheaper host (with a working motherboard) for the backend. Alas, the noisy frontend remains. It has an Athalon 3400 chip (too much, probably: it runs at about 40% CPU idle time while displaying live TV over a 100Mb Ethernet. It has an nvidia card, which was a good idea, though configuring the driver takes a little care.

You will probably never figure out how to get the AMD 64-bit Fedora kernel built and installed. But it isn't so much of an issue now.

The cheap Happaugh frame buffers (WinTV) are still available at CompUSA. MythTV works fine with them, but I am using one of the cards in the frontend simply as a remote control input.

QAM256 HDTV local channels are available on Patriot Media's standard cable fare, and it is probably required by law. But they omit the special information (I forget the techincal name at the moment) that lets the software find the channels. So I had to manually scan for and enter that appropriate information into MythTV. So I am using cable signals for HDTV, not off-air, and not the paid Cable HDTV channels. The scan notes:

	(see http://www.gossamer-threads.com/lists/mythtv/users/149939?page=last)
	bring dvb-apps up-to-date
	cd dvb-apps/scan
	dvbscan -vv -a0 -A2 atsc/us-Cable-Standard-center-frequencies-QAM256 
	
	[0002]:567000000:QAM_256:2049:2048:2
	[0003]:567000000:QAM_256:2112:2113:3
	[0001]:567000000:QAM_256:2176:2177:1
	[0002]:573000000:QAM_256:2048:2049:2
	[0003]:573000000:QAM_256:2113:2112:3
	[0001]:573000000:QAM_256:2179:2176:1
	FOX HD:579000000:QAM_256:2048:2049:2
	NJN-4:579000000:QAM_256:2112:2113:1
	[0003]:579000000:QAM_256:2176:2177:3
	[0002]:585000000:QAM_256:2048:2049:2
	...

The channel names are not necessarily correct, and some of the channels are useless, but this does find all the HDTV streams and sub-streams, including numerous digital radio channels. A manual examination of each channel using xine revealed which was which.

I let mythtv run a channel scan, which got a lot of incorrect results. These I repaired with mysql commands such as:

	select mplexid,sourceid,transportid,networkid,frequency,modulation,visible,sistandard,serviceversion from dtv_multiplex;
	delete from channel where chanid=2162;
	update channel set mplexid=9,serviceid=3 where chanid=2164;

THe HDTV has been worth the pain. It is gorgeous, even for aging eyes.