The release of VLC with Dirac support (via Schrödinger) and the release of the Dirac research codec (confusingly named dirac-1.0.0, sorry) has caused a bit of news in the geek press. I’ve noticed a few uninformed comments out there, and figured it would be wise to provide real information from a Dirac developer.
- Decoding Dirac takes a lot of CPU. This is true, depending on your definition of “a lot”. It is also on purpose. MPEG-4/ASP uses more CPU than MPEG-2, but gets better compression. Likewise with MPEG-4/AVC vs. MPEG-4/ASP. However, it doesn’t matter. A video stream either plays on a CPU or doesn’t. And most new computers (that aren’t specifically underpowered) are fully capable of playing Dirac at 1080p/30.
- Encoding Dirac can be slow. Right now, you either get slow and good (dirac-research) or fast and crappy (Schrödinger). This is an area of active development.
- Dirac and Theora will likely coexist. For a variety of historical and technical reasons, Theora encoder development has been concentrated on SD and smaller sizes (and corresponding bit rates) and Dirac encoder development has concentrated on SD and HD sizes and bit rates. And each currently appear to be better than the other in their respective areas. Given limited developer resources, I imagine this trend will continue.
- Tools exist for Dirac. Several will be released in the next few months, including both DirectShow and QuickTime plugins. (There are currently a few showstopper bugs remaining.)
- Comparing apples to oranges still doesn’t make sense. Many video encoders cannot be compared to each other because they focus on different problem domains. “1 Mbit/sec” is not a full description of how a particular video was encoded. That could mean CBR with a strict buffer model, or simply (file_size/duration), which are completely different creatures.
Also, there are Dirac demo videos here.