CoreAVC

CoreAVC is a proprietary video codec that is used for decoding MPEG-4 AVC or H.264 video formats.

The decoder is popular for its speed, which in some cases is on par with hardware-based decoders. CoreAVC is great for older PCs that include single core processors or worse, as it will allow for at least some type of playback of AVC content.

CoreAVC costs money however, and will run you $5-15 USD depending on what features you need. The decoder will not support H.264 Profiles 4:2:2 and 4:4:4, however.

Core works with many new Nvidia cards for extended decoding and was used in Joost (now defunct).