gstreamer: baseparse: add getcaps function

[Thiago Sousa Santos]

On Wed, 2011-11-16 at 10:51 -0800, Sebastian Dröge wrote:
> On Di, 2011-10-18 at 04:29 -0700, Thiago Sousa Santos wrote:
> > Module: gstreamer
> > Branch: master
> > Commit: e3f2d7db71dfb14441648033eb6cf3324ccc98b3
> > URL:    http://cgit.freedesktop.org/gstreamer/gstreamer/commit/?id=e3f2d7db71dfb14441648033eb6cf3324ccc98b3
> > 
> > Author: Thiago Santos <thiago.sousa.santos at collabora.com>
> > Date:   Mon Oct 17 14:42:08 2011 -0300
> > 
> > baseparse: add getcaps function
> > 
> > [...]
> >
> > +  if (klass->get_sink_caps)
> > +    caps = klass->get_sink_caps (parse);
> > +  else
> > +    caps = gst_pad_proxy_getcaps (pad);
> 
> Hi,

Hello,

> 
> this is completely breaking backwards compatibility with the old
> baseparse subclasses. Let's take two examples:
> 
> 1) h264parse allows to convert between different stream-formats. If
> downstream now requires a specific stream-format,
> gst_pad_proxy_getcaps() will propagate this singla stream-format to
> upstream and if upstream wants to provide something different
> negotiation will fail. But it shouldn't, h264parse can convert between
> the stream-formats. f3f9e4b9786d00299e0c6909180c4cd326489bdf fixes this
> in h264parse but it's nonetheless API/ABI breakage.

There was a patch for that in the h264parse in
https://bugzilla.gnome.org/show_bug.cgi?id=661874 waiting for review.
Was waiting it to be accepted before using the same approach on other
parsers that can do conversions.

> 
> 2) Consider a parser and downstream requests parsed=true on the caps.
> gst_pad_proxy_getcaps() will propagate the parsed=true field to the
> sinkpad caps and if upstream provides unparsed input negotiation will
> fail again.

I guess removing parsed/framed entries on caps can be added as a default
handling on baseparse.


The other option is to revert that patch and add a getcaps to all
parsers as the default getcaps gets the templatecaps. Template caps
won't have any other downstream restrictions on width/height/framerate
propagated.

--
Thiago

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