Re: high def mp4 render for devices with low quality video cards?

In general, you're going to need at least a decent dual-core processor -- and pretty much of all of it -- for camcorder-class AVC playback. The best place to start isn't messing with bitrate, since that's not your problem: your TV-PCs almost certainly have fast enough HDDs (assuming you're not trying to do this all over a network or something).

First thing, try lowering the complexity of the AVC. Try MainConcept rather than Sony AVC. MainConcept allows you to render high definition in the AVC Baseline profile, which is simpler to decode (and, simply put, I have found it decodes better on low-power devices, like tablets, than Sony, for whatever reasons). You might experiment around with "Tablet", "iPhone", and other settings designed for lower power devices.

If your TV-PCs have GPUs (unlikely, but check), you want those helping the decode. This is easy if you're running Windows 7, since the Microsoft AVC CODEC (built-in) uses the DXVA 2.0 API for GPU-enhanced decoding.

Another possibility is to render out to a higher quality HD format (high spec MPEG-2, camera-quality AVC, whatever) and use a more programmable encoder, such as x264 (TMPGenc, Handbrake). With enough control over the AVC format, you can make decoding much simpler, by eliminating B-Frames or even going all the way to AVC-Intra. This will also increase the size of the file needed to keep the quality the same, which is an issue if you're using networks, but no big deal on an HDD.

-Dave