[gstreamer-bugs] [Bug 595063] Support for parsers with easy codec install

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=595063
  GStreamer | gst-plugins-base | 0.10.x

--- Comment #5 from Tim-Philipp Müller <t.i.m at zen.co.uk> 2009-09-15 08:31:00 UTC ---
> All this still has the problem that the current missing plugin messages don't
> see a difference between decoders and parsers. So if you ask for
> decoder-audio/mpeg,mpegversion=1 you could get a parser but you could also get
> a decoder (which you don't want). So there should be a new message, etc for
> parsers/demuxers too I guess... What do you think Tim?

I think there's a valid use case here. Options I can think of:

a) just declare that distros are supposed to install all available elements
that match the caps when asked for a decoder, including elements with a rank
<MARGINAL. This might be what many do anyway. This approach has at least two
user interface problems though, namely 1) that the dialog says that you're
asking for a decoder whereas you are asking for a parser, and 2) if distros are
supposed to consider elements <MARGINAL, then in a playback scenario you might
end up with a situation where a decoder is missing, and the UI shows that it
installed a 'decoder' of some sort with rank <MARGINAL, but then playback still
doesn't work. Distros might currently avoid this situation by not listing
decoders for ranks <MARGINAL.

b) add a specific missing-element message for parsers

c) add a more generic missing-element message that would allow apps to request
elements via 1) element factory klass details, 2) input caps (optional) and 3)
output caps (optional). Ultimately (0.11) most of the other cases can be
replaced with this then. Distros will love this of course (not).


I don't see why we'd need a special message for 'demuxer' as well, I think
treating it as a decoder works well and a given caps format is either a
container or not, there's no ambiguity, is there? (I might add some helper
functions that return flags for a given caps, like if it's a container, if it's
parsable, if it's audio, etc., also see bug #549111).

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