Created attachment 234980 [details] [review]
proposed patch

when capssetter is followed by a capsfilter some element that wants to do upstream caps negotiation, capssetter just passes the sink peer caps upstream, which is definitely not correct.

These 2 test scenarios clarify the issue (both of which should work).

# Convert bayer pattern format
## worked
gst-launch-1.0 --gst-debug=capssetter:5 videotestsrc ! video/x-bayer,format=rggb,width=640,height=480,framerate=10/1 ! capssetter join=false caps="video/x-bayer,format=gbrg,width=640,height=480,framerate=10/1" replace=true ! bayer2rgb ! videoconvert ! xvimagesink
 
# Convert bayer pattern format, with additional capsfilter (that is identical to the capssetter's output caps)
## did not work
gst-launch-1.0 --gst-debug=capssetter:5 videotestsrc ! video/x-bayer,format=rggb,width=640,height=480,framerate=10/1 ! capssetter join=false caps="video/x-bayer,format=gbrg,width=640,height=480,framerate=10/1" replace=true ! video/x-bayer,format=gbrg,width=640,height=480,framerate=10/1 ! bayer2rgb ! videoconvert ! xvimagesink
 

A possible solution is to report any caps upstream (as included in the patch). In my opinion, this is the clearest.

I am not sure if this should be restricted further. I think it definitely should return 'any' in case of replace=true, yet for join=true, it might indeed make sense to  return a copy of the sink peer caps upstream. And without making it too complex, I can not immediately see a solution for the case of join=false and replace=true, so my suggestion is to always return 'any' upstream regardless of join/replace (it's a debug tool, so capsfilters will work as well).