Perian, a free open-source plug-in that enables QuickTime support for a wide variety of video formats, has been updated with additional video format compatibility and fixes. Version 1.2.2 of Perian was released yesterday and is available from the download page at Perian.org.
This week's update added compatibility with WebM/VP8, FFv1 lossless video formats, and compressed MKV files, as well as bug fixes involving Matroska file importing and reading. The full list of changes in version 1.2.2 can be found in the version history section on this page.
Notably, the 1.2.2 version notes indicate that older versions of Mac OS X will no longer be supported in future versions of Perian:
The next planned version will remove support for PowerPC and Mac OS X versions prior to 10.6. Maintenance updates may be provided if necessary.
Perian 1.2.2 requires Mac OS 10.4.7 or higher.