HT doesn't actually make video encoding go any faster. It just allows the system to remain more stable while performing some other task at the same time. You really should not be running other tasks on your system while encoding video, your encoder will need all the resources it can get.
Uh, are you sure of that? My experience has been that x264, for instance, benefits greatly from hyperthreading.
Hyperthreading allows you to queue up additional instructions (in a different thread) that the executor can switch to when it would otherwise be just waiting for the next instruction in the primary thread.
You are correct that x264 does benefit from hyperthreading. According to the devs, the speed increase is about 20% until you are on the veryfast or ultrafast presets, which at this point is usually bottlenecked by decode speed, and not the speed of the encode.
In making my previous claim, I was limiting the concept of 'encoding' to the more old-school definition: lossless compression of media bytestreams. This would include things like HuffYUV, ProRes, etc. But to be fair, these days it is quite likely that even a few of the newer intermediate/mezzanine codecs benefit from hyperthreading. I'd edit my post to clarify but the edit window has passed.
