MythTV HD Playback



MythTV HD

If you have a High Definition TV, you'll be pleased to know that MythTV supports the recording and playback of HD content. Best of all, it works out-of-the-box on Karmic and later! The main thing you need is a compatible graphics card. Read on...

Recording

To record in High Definition, you need an HD broadcast and a compatible tuner card. In the UK there are two options:

The HD broadcasts are full quality 1080p, so you need a big hard drive (45mins=6GB!).

Playback

Unless you have a very powerful machine, using a dedicated MPEG4 decoder chip is the only way to go when playing HD content. One way to do this is to use an nVidia graphics card which supports VDPAU. This allows video programs to offload portions of the video decoding process and video post-processing to the GPU video-hardware. Using it, you can play back full HD videos with negligible CPU usage. Note also that it also offloads SD content, making it viable for very low powered, efficient machines to be used.

VDPAU has worked out-of-the-box since Ubuntu Karmic and Myth 0.22. All you have to do is set your Playback profile to VDPAU. Go to Utilities/Setup->Setup->TV Settings->Playback->Playback Profiles (3/9) and set the Current Video Playback Profile to one of the VDPAU options. VDPAU Normal works best for me on my Acer Revo, but try each of them to see which works best for you.

TV-Out

Many of the latest nVidia cards, including the one built into the motherboard mentioned below, come with both DVI and HDMI outputs. Assuming your TV has an HDMI input, you can either use a DVI to HDMI cable or an HDMI to HDMI cable. The latter is the better option because it allows sound as well as pictures to be transmitted to your TV.

Tips and Troubleshooting

There are quite a few tweaks which may be required to get VDPAU to play recordings smoothly. Read the following page very carefully, especially the "Troubleshooting" section. You will probably have to set "PowerMizer" mode to "Prefer Maximum Performance" in nvidia-settings:

Additionally, if you still see the Gnome panels at the top and bottom of the screen when mythfronted is running, disable visual effects by going to System->Preferences->Appearence and setting Visual Effects to None.

To prevent combing effects during playback, it is recommended that you not only disable visual effects but composting altogether. This can be done by simply adding the following line to your /etc/X11/xorg.conf

Section "Extensions"
  Option "Composite" "Disabled"
EndSection

Even though much of the processing is offloaded to the GPU, picture breakup has been known to occur due to the processor stepping. To get around this you can make sure the CPU clock doesn't step down too far, eg:

cpufreq-set --min 1.8g

Note that the above command may not be necessary, depending on your system. My advice is to try without it first.

Hardware

nVidia Ion nettops, such as the Acer Aspire Revo, make perfect HD frontend boxes. They support VDPAU and HDMI and are almost silent. They look great, but are small enough to hide. Best of all, you can get Linux versions for between £130 and £190, depnding on spec.


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