REGRESSION: Stateless decoders won't autoplug anymore because of vp9alphadecodebin template caps
The following discussion from !1012 (merged) should be addressed:
I think I found why, it's a regression introduced by vp9alphadecodebin, it's template caps does not include the alignment, is first to contribute to parsebin capsfilter caps. So vp9parse will simply pick random default. I think the simplest solution is for alpha wrapper to expose the internal decode alignment. I guess I could go further and copy the template, this way we don't have to keep it in sync.
cc @seungha.yang as this likely breaks auto-plugging of d3d11vp9dec.