If the MPEG4 encoder block can "only" take 50% of the 960x540x240 rate .... then could the GPU be assigned enough memory for burst captures for a buffer?
if thats 150MB/sec uncompressed at the 10bit setting, have say a 512MB buffer, and thats towards 6 seconds of capture if the encoder is emptying from the front of the queue at full rate. Its no different than the mechanism used for the first few secs on a DLSR taking stills for example
I can think of many many things where that would be a great feature.
Note this could also work for the other readout rates.