Monday, 26 April 2010

Diary of an x264 (mbaff) developer

I've just found out officially that I've been accepted into the Summer of Code program! This means that following university exams I'll be working developing a new interlaced encoding method for my favourite video encoder: x264.

Interlacing is the process of taking two consecutive pictures (called fields) of video that are often captured slightly after one another and merging them together into a single frame. Many professional video cameras do this in their usual operation. The up-side of this is you can have the high frame rate that comes with presenting two pictures in the space of one, but the downside is that each field has half the vertical resolution of the equivalent frame.

Macroblock adaptive frame-field interlacing, or mbaff for short, is a method of encoding interlaced video that makes a decision on whether or not each individual macroblock should be interlaced. The traditional method, and that currently implemented in x264, is to keep each frame fully interlaced. However, it is preferable to encode a macroblock with low movement in it as progressive, as this is more efficient. MBAFF interlacing is one of the few major features that most H.264 video encoders currently support that's missing in x264.

I hope to see significant improvements in the efficiency of interlaced encoding when this project is completed. Until then, I'll post regular updates of my progress.