'video' makes me wonder if there's a way to 'hack' an encoder (h264/avc?) to use P- and B-frame information to mark moving areas (that's what they're supposed t

'video' makes me wonder if there's a way to 'hack' an encoder (h264/avc?) to use P- and B-frame information to mark moving areas (that's what they're supposed to be good at) so that "only" still data (I-frame minus what moved) remains. Now you've got a lot less data to churn. Also, in this process, could marking pixels with "stillness" probabilities resulting in some blending factor (alpha channel?) before flattening the I-frames thing work?