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Www.MythTVr1.10 - 08 Feb 2007 - 17:48 - BenScotttopic end

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Introduction

On Thursday, 18 Jan 2007, MerriLUG was proud to host Jarod Wilson, who presented on MythTV. 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. Jarod 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.

The MythTV home page is http://www.mythtv.org. There is an official MythTV wiki, and a source code/bug tracker.

Jarod Wilson works for Red Hat in Tyngsboro. He is one of the authors of Hacking MythTV (Wiley). Sample chapter online: MythTV Performance Hacks. Jarod's web site includes a section on Fedora Myth(TV)ology, which includes a detailed HOWTO guide.

What is MythTV?

MythTV is Free Software which runs under the Linux operating system, and provides the functions commonly known as a PVR/DVR (Personal/Digital Video Recorder). Essentially, it's a computerized, intelligent VCR, which uses hard disk instead of tape, and knows when shows are on so it can record them automatically. TiVo and ReplayTV are two commercial DVR products. Since it's open source software, if you don't like the way it does something, you can always change it that's how much of its current functionality came about in the first place.

MythTV includes all the basic PVR functions, like recording and playing back scheduled programs, allowing you to schedule recordings automatically in advance, and pausing and rewinding live TV. MythTV also has a plugin system which permits it to be extended by other programmers. Plugins currently exist for playing external video, viewing photos, listening to music files, using your TV and a web camera as a video-telephone over the Internet, browsing the web, retrieving current local weather, and many other functions.

There is a Gallery of MythTV setups if you want to see what it can look like.

MythTV Operations

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 some 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 separate music-playback into its own program. That will let one play music while browsing the web, viewing a photo gallery, etc. This is expected to be available Real Soon Now.

The MythTV wiki includes information relating to the operating system. This is of interest mainly because it has links to projects like KnoppMyth -- a "Live CD" which includes a canned installation of MythTV. Just put the CD in the computer and turn it on.

Broadcast technologies

Lingo

  • Standard Definition (SD): The TV picture we've been watching for decades. 480i (480 interlaced lines). 640x480 resolution. Can be distributed via analog or digital means.
  • High Definition (HD): The new TV picture. Various better displays, including 720p (720 progressive, non-interlaced lines) and 1080i. Surround sound capable. Digital only.
  • Analog: The traditional over-the-air or cable TV systems we've been using for decades. Limited to Standard Definition.
  • Digital: New over-the-air broadcast and cable systems are digital. All High Def TV is digital, but not all digital is High Def.

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 unscrambled, 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 controlled 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.

Compatibility matrix

Read from left to right. "Scrambled" indicates deliberate action is taken to make it hard for anything (MythTV included) to capture the content.

Delivery Signal Picture Programming Scrabled? MythTV
Over-the-air Analog Std Def Local Stations Never Works great
^ Digital Std Def Local Stations Never Works great
^ ^ High Def Local Stations Never Works great
Cable Analog Std Def Local Stations Rarely Works great
^ ^ ^ Basic Cable Rarely Works great
^ ^ ^ Premium Cable Usually Possibly, if MythTV can control the cable box via "IR blaster"
^ Digital Std Def Local Stations Sometimes Only if not scrambled
^ ^ ^ Basic Cable Usually Unlikely
^ ^ ^ Premium Cable Usually Unlikely
^ ^ High Def Local Stations Sometimes Only if not scrambled
^ ^ ^ Basic Cable Usually Unlikely
^ ^ ^ Premium Cable Usually Unlikely
Satellite Any Std Def Any Either Possibly, if MythTV can control the satellite box via "IR blaster" or serial cable. Video capture is limited to analog Std Def.

Hardware

Tuner/Capture Hardware

PVR Hardware database has a list of configurations known to work, notes, etc.

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 Jarod 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

Jarod 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 archiving 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.

Recommended vendors

Jarod Wilson's list of "good places to get hardware":

Other resources

About this document

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

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