Compressor: What is Frame Reordering?

Ever wonder what this checkbox does in Compressor?

Me, too. So, I went on Apple’s website and learned:

Frame reordering is the concept of allowing frames to be decompressed in a different order than their display order. For almost all cases, leave this box checked for H.264 encoding. Some more advanced compressors use “frame reordering” to more efficiently represent movie data.

The only time you would uncheck this box is if you are creating an H.264 movie that needs to be played back by an application that does not understand frame reordering, i.e., an application that does not yet use the new Frame Reordering APIs of QuickTime 7 or if someone asks you to create your content with “B-frames turned off.” If your audience will play back your movie with QuickTime 7 Player, you should leave the box checked.

Since QuickTime 7 has been out for years, make a point to turn Frame Reordering on. Also, frame reordering is a good idea when creating video for mobile devices.