When allocating aux buffers for postprocessing, it's assumed that base
buffer size is the same as that of output. Coincidentally, that's true
most of the time, but not always. 10-bit source also needs aux buffer
size which is appropriate for 10-bit native format, even if the output
format is 8-bit. Similarly, mv sizes and other extra buffer size also
depends on source width/height, not destination.