When the first frame of a telecine pattern did not generate an output
frame (because it is a 0 or a 1), this could lead to the first two
output frames getting equal pts values.
When the first frame of a telecine pattern generates exactly one output
frame (i.e. when the telecine pattern starts with 2 or 3), then the
output was correct before this comment, and still is unchanged.
When the first frame of a telecine pattern generates more than one
output frame (i.e. when it starts with 4 to 9), then output pts are
still broken. This is not really solvable without knowing the frame
duration, or delaying output by one frame.
This is done by requesting a buffer from the next filter in the chain, instead
of always allocating our own. This allows the next filter to e.g. ensure its
own preferred memory layout.
