Perhaps the next most obvious task for a powerful CPU in a desktop PC is video encoding. Whether it's for editing your family videos or re-encoding your favourite videos to an iPod-friendly format, video encoding is becoming more and more common and so we've used two scenarios for testing video encoding performance.
The first is our age old test of re-encoding a portion of DVD quality MPEG-2 video into the open source Xvid format. This test is a bit long in the tooth as the version of Xvid we use is quite old so not multi-threaded (not to mention the fact that the source footage isn't even HD) but in being so it gives us a very reliable indication of single-core performance.
The next scenario takes a section of 1080p footage, again in MPEG-2 format, and re-encodes it into the h.264 format. This is a much more up to date test as the source material is Full HD and the h.264 codec is about the most advanced video format currently available. We also use the open source converter, AutoMKV, for this task, which fully supports multi-threading.