One video sink with multiple sink pads

[Carlos Rafael Giani]

Hello,

I wonder if a video sink with multiple sink pads is feasible. All sinks 
I have seen so far use only one sink pad.
Could multiple sink pads in theory lead to problems? I am thinking of 
all the efforts for prerolling, asynchronous state changes and so on.

I was thinking of using a GPU here for effects like picture-in-picture. 
An alternative of course is to compose the various input frames into one 
output frame in a transform element which uses the GPU.
However, the problems with this approach are: (1) requires either an 
offscreen context (may be buggy with some drivers) or a small window 
somewhere where this is rendered,  (2) additional effort required by the 
GPU, since the compositing would not directly go to the output 
framebuffer, but to an offscreen one instead, which is why I thought of 
putting this into the sink directly, to not waste MIPS.

Thoughts?