On Thr 18 Jan 2007, MerriLUG was proud to host Jared Wilson, who presented on MythTV. This page is an attempt to collect some of the notes about the presentation.

The MythTV home page is: http://www.mythtv.org

Jared's home page is http://www.wilsonet.com/ , which includes a section on Fedora Myth(TV)ology and links to his recently-released book from Extreme Tech. There's a sample chapter on that website, too.

Sixty-one attendees made it to Martha's Exchange that night, making it the largest dinner ever, and one of the largest meetings, ranking up with Ted T'so and Linus. Jared ran the meeting as a straight Q&A after a brief introduction, and finished with some striking demonstrations of the difference in quality between SD and HD captured video.

How it works

The MythTV system downloads it's Electronic Program Guide (EPG) data from Zap2It.com, via an XML export feature. Zap2It requires free registration for this. Zap2It's motivation is apparently to avoid tons of screen scrapers hammering their web servers. Zap2It is operated by Tribune (incidentally, TiVo uses the same company for their EPG data). EPG is available 12 days ahead of airdate.

If you have multiple MythTV boxes, you really should try and make sure they all have the same version. Compatability between versions of MythTV is not good.

To show "live TV", MythTV records the live feed and then "immediately" plays it back again, in near-real-time. However, there is a lag introduced. Direct "pass-through" (without the record-and-play method) is not currently supported. This is being worked on.

Another feature being worked on is to put music-playback in a separate process. That will let one play music while browsing the web, viewing a photo gallery, etc. This is expected to be available soon.

Broadcast technologies

  • SD = Standard Definition. The TV we've been watching for decades. 480i (480 interlaced lines). 640x480 resolution. Can be distributed via analog or digital means.
  • HD = High Definition. The new TV. Various better displays, including 720p (720 progressive, non-interlaced lines) and 1080i. Digital only.

Over The Air

OTA = Over The Air. These are the TV signals broadcast from transmission towers and received via antenna at viewer sites. Think rabbit ears and roof-mount Yagi antennas. OTA still exists and can work fine, even in this era of cable and satellite. If your house is conveniently placed to receive the signal, digital OTA can be of very high quality. And you can't beat the price.

OTA exists as two major types. Both are unencrypted and can be recorded by MythTV. Analog OTA (NTSC) is the classic analog TV system that's been around for decades. Analog TV is SD programming only. There are lots of tuners for NTSC. Digital TV (ATSC) is the new standard. It enables HD (High Definition) programming, but allows for SD as well. You need a digital tuner to receive ATSC, but they exist, too.

In southern NH, the big OTA stations are TV 2, 4, 5, 7, 9, 11, and 25.

Cable TV

First, a definition: "Basic cable" designates all the flat-rate channels you receive with a basic cable package, like History, Discovery, CNN, ESPN, TBS, etc. Basic cable does not include "premimum" cable, like HBO, Cinemax, etc.

Cable TV also exists in analog and digital flavors. As with OTA, analog cable is limited to SD. In this area, analog basic cable is generally transmitted unscrabled, so you don't need a decoder box. That means it can work well with MythTV. Premium analog cable needs a cable decoder box. It is unknown to this author if such a decoder box can be hooked up to, and controled by, a MythTV system.

Digital cable is a tricker beast. Most digital cable channels -- even basic cable -- are encrypted on the cable wire. Digital cable boxes and high-def TVs include sophisticated mechanisms designed to prevent you from recording it using your own hardware. This means MythTV is not going to work for most digitial cable channels.

Cable TV providers redistribute the high def, digital feeds from the local OTA stations. The signals are generally re-modulated, as digital OTA broadcast uses 8-VSB, while digital cable prefers 256-QAM. However, the local broadcast programming is often not encrypted -- so called "QAM in the clear". If that's the case, you can make use of it with MythTV. You generally don't even need to subscribe to "digital cable" -- the unencrypted feed comes down all the cable wires, regardless of subscribed services. If you already subscribe to basic analog cable, this can be an easy way to get a few HD channels, without messing around with antennas or paying extra for digital channels.

Per FCC rule, any modern (within the past few years) digital cable box must have a FireWire port, which can provide the digital video bitstream. Thus, if you have such a cable box and a FireWire port on your PC, you don't need a tuner/capture card. However, the bitstream will still be encrypted for most channels, so it doesn't solve that problem.

Tuner/Capture Hardware

Any card needs to be Video4Linux (V4L) compatible. There are dozens of compatible cards. Check the MythTV website for information on what works and what does not.

The Hauppauge WinTV PVR line is popular. Some notes on models:

  • PVR-250 is a good started. The IR receiver (for remote control) is not the best.
  • The hardware decoder on the PVR-350 is of limited use.
  • The PVR-500 is a dual-tuner card, and functions just like having two PVR-250 cards.

One bit of hardware that Jared recommended was the HD Home Run, from SiliconDust. It is basically an Ethernet-to-TV bridge. You plug coax into one side, Ethernet into the other, and you're in business. It contains everything you need to tune, capture, encode, and stream a TV signal over the 'net. It can be used with MythTV and other software as a capture device. This lets you put your TV input hardware in a different location than your MythTV backend storage hardware.

Other Hardware

Jared recommended NVidia video display hardware, with the binary-only, closed-source driver. He also recommended the use of the a config tweak in the X server configuration file: Set UseEvents to be True. He said the ATI cards can sometimes be made to work, but sometimes not, and all require too much effort.

Lots and lots of disk storage. The more, the better. Standard definition recordings consume about 2.5 gigabytes/hour. High definition recordings consume from 6 to 12 gigabytes/hour.

MythTV has an archving plugin for archiving to DVD.

Any LIRC device (IR remote control) will work.

For playback, a 600 MHz PIII is minimum for std def. High def needs a lot more, perhaps a 2 to 3 GHz P4 or similar. There are a lot of things you can do in the area of performance tuning.

Network streaming (i.e., a recording stored on one box, playing on a different box, over the network) is possible. MythTV uses its own protocol, or you can use NFS/etc. Std def needs about 3 megabits/second. High def can use up to 17 megabits/second. Avoid wireless (802.11) -- even if nominal throughput is there, contention and packet loss will kill you.

Other resources

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Provided AS IS. Use information here strictly AT YOUR OWN RISK.

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Revision: r1.4 - 22 Jan 2007 - 23:15 - BenScott
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