basesrc: re-negotiate caps in pull mode if necessary
Submitted by Matthieu Bouron
Link to original bug (#733921)
Description
This patch solves the case when basesrc is stuck in pull mode and never get the chance to negotiate with downstream (to use a custom memory allocator for example).
It happens when typefind is plugged downstream, with the following scenario:
filesrc ! typefind ! demuxer (proposing a custom memory allocator).
Not sure if the patch is 100% correct though.