encodebin: enable splitmuxsink use
Submitted by Jan Schmidt
At the moment, it's not possible to use splitmuxsink with encodebin, because encodebin outputs already-muxed content to a single ALWAYS src pad.
To work with splitmuxsink, we need to delegate both the muxing and output to an internal element.
Attaching patches that create a new encodebin which has no source pad and does the required delegation. I've called it splitencodebin because that's the primary use case, but really it could be used for other purposes too. If anyone has a better more-generic name, speak up. Or, we could call it 'encodebin2' and give it a SOMETIMES src pad that makes it work as the current encodebin does.