It is analogous to Variable Bit Rate mp3 audio encoding. No, it would be analogous to variable sample rate audio encoding, which doesn't exist. It should also

It is analogous to Variable Bit Rate mp3 audio encoding. No, it would be analogous to variable sample rate audio encoding, which doesn't exist. It should also provide a way to degrade gracefully to output devices that don't support high frame rate. Hierarchical B-frame structures in H.264 already provide this feature. For example (where A is the highest level, B middle, C lowest, and P frames are "ordinary" frames): Full framerate: P A B A C A B A P Half framerate: P B C B P (drop the As) Quarter framerate: P C P (drop the As and Bs) Eighth framerate: P P (drop the As, Bs, and Cs) This is possible as P/B/C can't reference As, P/C can't reference Bs, and P can't reference Cs. Some broadcast hardware encoders are known to use an even more extreme structure that involves 15 frame per hierarchy, allowing down to one sixteenth of the framerate.