2010-03-12
Changes to Firefox YCbCr Color Conversion Code
I posted previously about colour conversion libraries. To replace the liboggplay conversion routines we decided to try the Chromium libraries.
Bug 551277 adds the Chromium code and integrates it with the new video layer painting code. The Chromium code uses a C fallback if MMX is not available but this is done at compile time. I modified it do runtime detection using Mozilla's SSE.h and moved the generic C routine from the Linux specific implementation to be used on all platforms that don't have MMX. Some other minor modifications were done (function name, namspacing).
I added an 'update.sh' script that can be used to update against the latest Chromium code. Given the path to the Chromium source it applies a patch for the changes I made.
Bug 551378 adds YCbCr 4:4:4 conversion (YV24). The Chromium code supported 4:2:0 and 4:2:2 (YV12 and YV16 respectively). Theora also allows 4:4:4 per spec. There aren't many 4:4:4 Theora videos out in the wild and the fix in this bug only adds support in the slower C implementation. I detect if the video is a 4:4:4 video and fallback to the C code.
At some point optimized MMX routines should be done for this. I've raised Bug 551844 for this. This would probably make a good first bug for anyone who wants something small and self contained to work on. It would be good to contribute this back to Chromium when done too.
Xiph has a test suite with example videos in the different formats.
