[packagekit] GStreamer Structure

Richard Hughes hughsient at gmail.com
Sun Dec 7 00:49:03 PST 2008

On Sat, 2008-12-06 at 15:49 -0800, Sebastian Heinlein wrote:
> recently the provided Gstreamer plugins have been added to the package
> meta data in Debian and therefor in Ubuntu too.

Great news.

> When making use of this in the APT backend, I was wondering about all
> the structure rewriting which happens.
> This is an example request of GStreamer which it gives to the installer
> plugin (in this case requesting for a mp3 decoder):
> gstreamer|0.10|totem|MPEG-1 Layer 3 (MP3) decoder|decoder-audio/mpeg,
> mpegversion=(int)1, layer=(int)3 (MPEG Layer 3 (MP3) decoder
> An here is what PackageKit gives to the backend:
> gstreamer0.10(decoder-audio/mpeg)(mpgversion=1)(layer=3)

This is the most concise string we could use as a descriptor without the
string description. We also use this as the "provide" string used for
the packages in Fedora.

> What I need is to get the Gst object type and the structure to convert
> it into caps again:
> Package.hasGstreamerPlugin("decoder", "audio/mpeg, version=1, layer=3")

What format is the package metadata in? Can't you just use a flat string
like "decoder-audio/mpeg, mpgversion=1, layer=3" -- or do you have to
break the decoder field up?

> Could we try to find a format which would avoid all this rewriting?

To be honest, I think all the backends are going to implement this
different ways, and encode the data slightly differently, and that we
just have to document the different formats.


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