Build a MythTV Box without Breaking the Bank

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How to turn your old PC from a dust magnet into a state-of-the-art media center.
Performance

You may run into a few problems on your low-end system. The two main ones involve high CPU usage and insufficient RAM. You can operate MythTV with 256MB of RAM; however, I experienced frequent freeze-ups, so I upgraded to 512MB. You should keep an eye on how well it's performing and consider upgrading if necessary. Another problem I experienced early on was that playing recordings or DVDs consumed such a large fraction of CPU time (70%–80%), that running other processes tended to cause the playback to become jerky. In particular, commercial flagging and database accesses at the beginning and end of recording a program produced annoying jerkiness. I resolved this problem entirely by replacing my ATI video card, which does not have a proprietary Linux driver, with an NVIDIA card. The skipping stopped almost completely when I replaced the video card, as did the seemingly unrelated problem of slow menu scrolling. CPU usage dropped to around 40%–50%.

Another benefit of NVIDIA's superior Linux support is that part of the MPEG decoding work can be delegated to the video card using XvMC (X-Video Motion Compensation), reducing the load on the CPU. To enable XvMC, go to Utilities/Setup→Setup→TV Settings→Playback. On the third screen, change the Playback Profile to CPU--. XvMC didn't kick in on mine until I deleted the top line of the profile (referring to ivtv). You can tell if it's operating because the on-screen display changes to grayscale. You also can tell because the CPU usage will go way down. The Xorg process dropped to less than 10% during playback; the sum of Xorg and mythfrontend is always less than 30%. As a result, additional processes (including creating and burning DVDs) no longer affected playback.

Figure 5. Enabling XvMC under TV Settings

Satisfaction

For a pretty small sum—$85 if you get a tuner card on sale and already have a computer and up to around $500 for a multicard, multidrive system built from scratch—you can build a fully functional MythTV box. TV watching will never be the same.

Be warned: MythTV is an amazing piece of software, but it is free software that is constantly under development. Be prepared to get your hands dirty and tinker under the hood if something goes wrong or everything isn't working as you'd like. Have fun with it—test-drive different themes, tweak the settings and try the various plugins. After all, that's what Linux is all about.

P. Surdas Mohit is a postdoctoral fellow at the Institute of Geophysics and Planetary Physics at Scripps Institute of Oceanography.

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