Table of Contents

• Part 1 – Introduction
• Part 2 – Hardware
• Part 3 – Base OS
• Part 4 – Prerequisite Software
• Part 5 – MythTV
• Part 6 – Configuration
• Part 7 – Conclusion

The MythTV box has been a happy member of the family for a couple months now. It is time to look back on the experience.

Overall the system has worked well. We haven't had any system lockups other than the ring buffer problem. (In 0.17 when the ring buffer fills while watching live tv, mythbackend crashes. Hopefully this will be fixed in the next version.) Initially the video would become jumpy after operating for a couple hours. This doesn't seem to be a problem now. We also noticed that the video lagged the audio by a small but noticeable duration. This was fixed by the turning on "Synchronize to video" in the configuration. Finally when we first start watching live tv we would get slight pauses in the video and audio. These were accompanied by “prebuffer pause” in the log file. Generally the problem would gradually stop after some 5 to 10 minutes.

Program Data Download

At some point the program data download from labs.zap2it.com stopped working. Everything seemed fine on our end so we logged into the zap2it website. There we noticed that our channel configurations were gone. I think what happened is our cable company changed the names of the channel lineups. The ones we selected previously were gone.

To fix the problem we selected new channel lineups for our account. Then we modified the MythTV setup to use the new lineups. It has worked fine since.

CPU Utilization

Watching live tv at 720x480 resolution has about 50% cpu utilization for mythfrontend. This is split about 25% user space and 25% system space. This split is due to the MPEG hardware acceleration of the VIA EPIA motherboard. mythbackend runs about 2% due to mpeg encoding done on the WinTV card. Overall the system runs about 60% cpu utilization watching live tv.

Running mythcommflag to flag commercials while watching live tv takes the remaining cpu. However the "nice" level is such that it doesn't cause any problems. At about 50% (nice), mythcommflag crunches through the files at about 40 frames per second. We do see more “prebuffer pause” when running mythcommflag so we run it as a cron job late at night instead of running it automatically as shows record.

At one point we selected "deinterlace" in the options. The image looked good but was occassionally choppy. It drove cpu utilization to 100%. We turned that option off.

One area that was a little surprising was the recorded video page. That page shows little, live thumbnails of the recorded show. Although we didn't notice it at first, that little image would play for a second or two, pause, then play for another couple seconds, pause, etc. Looking at the cpu utilization while on that page showed over 95% utilization. Apparently the video scaling is very cpu intensive. There is an option for "cpu friendly previews" that cuts the framerate down to make previews less of a cpu hog. We turned that option on.

Here is a table that shows our cpu utilization under various operating modes.

Remote Control

If you've looked around on the website you'll see that I am not a big fan of infrared remotes. We created a patch for MythWeb so we can control MythTV via a web page. We also created a Pocket PC application to control our system. Unfortunately both thems have a fairly low FAF (family acceptance factor). I have to admit that the Pocket PC, while handy, doesn't quite have the feel of a traditional remote.

While we still use the web and Pocket PC remotes, we've added a wireless keyboard to our system. This works well when we need to do more complex tasks on the system. To increase the FAF we're going to extend the wireless keyboard option to also work with an infrared remote. This remote is programmed to emulate the wireless keyboard for common commands. Now the family uses the MythTV system just like a “store bought” electronic device.

Other Changes

The volume was often too low on the system. We would typically run the volume at 96% or 98% and it would be ok but didn't give any headroom when things got noisy. Opening a shell we could see that the mixer was only 22 in a range of 0 to 31. We could increase this to 31 and improve the situation significantly. Unfortunately the volume would reset to 22 when the system was restarted. Alsa is suppose to save settings but obviously didn't. Instead of debugging that problem we just added the following line to our /etc/conf.d/local.start file:

amixer set Master 31 2>&1

This way the volume is set to maximum in the mixer whenever the system starts. Now volume isn't a problem.

The only other change we've made is to run mythcommflag as a daily cron job. Since we let our MythTV system run 24 hours a day we can program it to run mythcommflag in the middle of the night so it doesn't interfere with recording or watching tv. To do this we added the following to /etc/crontab:

5 2 * * * root /usr/bin/mythcommflag

This will cause mythcommflag to run automatically every night at 2:05 am.

Conclusion

MythTV is a great application. It is full featured and quite stable. The VIA EPIA systems has also worked well. MythTV has a reputation for being difficult to install. It is hard but there is help. My recommendation would be to stick with configurations that are known to work. Often I see people that pick up a component here, another there, then try to build a system. Usually this will work, eventually, but will entail considerable effort. In other words, approach the system from the other end. Start with “I want a MythTV system” and here are the components that will give it to me instead of “I want these components” now let me try to build a system.

What we've done here is work through the issues for a particular platform. We know that this combination of components will work. If you are interested in a different platform try to find combinations of components that are known to work together. Unless of course you are more interested in the challenge. That's cool too.

Shameless Commercial Plug

What can I say, we have bills too. Along with this tutorial we put together a kit that includes all of the hardware used. We also have complete systems ready to use. The wireless keyboard and pre-programmed infrared remote are useful no matter how you built your system. And of course we have the individual components in our store. Take a look!

Complete MythTV System
MythTV Hardware Kit
Wireless Keyboard
Pre-programmed Infrared Remote

History
16 May 2005	Initial publication

Tim

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Published on: 2005-05-15 (6288 reads)