Last input frame.
If you set the FILTERPARAM_NEEDS_LAST flag on exit from paramProc,
fa->last will point to a bitmap holding the last input frame. This is
useful for temporal filters. Unfortunately, at this point, it only holds the last
frame input to the entire filter chain. This will probably change in the
future.
initProc and deinitProc functions.
These functions allow you to initialize variables in a filter instance's data block
on creation and to clean it up on destruction. initProc can return a nonzero
value to abort filter instance creation if resources are not available. Note:
Most, if not all, allocations should be deferred to startProc.