[Bug 634407] decodebin2 should expose pads in a deterministic order

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=634407
  GStreamer | gst-plugins-base | unspecified

--- Comment #52 from Sebastian Dröge <slomo at circular-chaos.org> 2012-08-04 08:33:35 UTC ---
(In reply to comment #49)
> > (In reply to comment #47)
> > > My hope for this functionality is that I can get a name/object for each stream
> > > from discoverer and then when I want to plug things to decodebin I can use
> > > those names/objects to identify the stream I want, so in the sense that I hope
> > > to just use objects and not string recognition I am fine either way.
> > 
> > This will only work for the case when the source implements the URI handler
> > interface and has an URI... or the source somehow (see above) provides another
> > deterministic stream-id. The default case would provide a random stream ID.
> > 
> > In any case, after these changes and after they are implemented wherever
> > needed, you will be able to match streams by doing a string comparison of the
> > stream-ids.
> 
> How would the matching help if the stream-ids are generated with a
> random-number generator? Wouldn't it make more sense to hash the caps?

The PRNG is only used for the case when the URI query returns nothing and
there's no upstream stream-id yet. Problem with hashing the caps is that
they're not unique, not even in the same pipeline.
For the cases when there's no URI for the stream we would need another solution
like the one I mentioned above, but that can be added later.

Also, with these stream-ids it would now be possible to sort the streams inside
decodebin/playbin to have a deterministic order of pads/streams.

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