The problem with hardware accelerated video playback is that the company creating a 'consumer product' sold to an 'end user' has to pay the royalties to the MPEG-LA.
So any chip maker like VIA is not required to pay the patent licensing royalties since they just produce an 'intermediate product' which somebody else can turn into a 'consumer product'.
This works fine in an environment where VIA makes chips and provides reference driver code under NDA to a system integrator, who then sells a bundle of software and hardware to an end user. In that case the system integrator either pays the royalties and can sell that product, or doesn't pay the royalties and can just sell the hardware without the proprietary software drivers and programs to actually make use of those hardware features.
Now imagine the open source situation for this. If VIA was suddenly selling chips as intermediate products, but also disclosing free player software to make use of that acceleration features? Would that then be a 'consumer product'? Who knows. But it would definitely be distributed to an 'end user' since it's available to anyone who wants to download it.
So if any independent free software or proprietary software program implements those codec acceleration features, they might violate the patents on those video codecs. Just in the same way mplayer, xine and other FOSS programs do not pay the per-installation/copy/download royalties for MPEG2/H.264/... playback products. Maybe you can call a sourcecode implementation just a 'reference implementation for scientific purpose', but that's open to legal interpretation and as far as I know there is no precedent in this area. But it is their decision on what legal risk they take.
It's the very same reason why distirbutions generally refrain from shipping that player software. Because there is significant indication that they would have to pay per-unit royalties. And with free software, you never know how many units there are, so you don't even know how much to pay - and you also have no revenue from things that you don't sell...