[gst-devel] tags

[Benjamin Otte]

On Sun, 28 Dec 2003, Colin Walters wrote:

> On Sat, 2003-12-27 at 05:42, Benjamin Otte wrote:
>
> > The correct solution for me seems to be plugging the complete pipeline as
> > you'd plug it on playback since that's the only way you can be sure to get
> > all the tags.
>
> I'm not sure I understand.  How do you propose get the tags?  Would it
> be by connecting to a signal on the decoder?  How will tag writing work?
>
Tag writing is completely different from tag reading. This is because you
extract metadata from files, that cannot be changed (like length or
bitrate).

I'll illustrate the reading part some more:
  src ! typefind ! spider ! audio/x-raw-int ! fakesink
(maybe replacing fakesink with a tagsink that supports tag reading better)
This pipeline should be close to what you use for playback. If you use
this for an mp3, spider will (soon again) plug this to the equivalent of
  src ! typefind ! id3tag ! mad ! fakesink
id3tag will then read the id3 tags. It can however not read audio specific
tags like bitrate or length. This should however be easy to implement in
mad.
Now you set this pipeline to playing and wait for the first buffer to
arrive on the sink. Tag events arrive before buffers do, so you'll have
the tags by then - including length.
If you used a tagsink or similar you'd collect the tags from the events
there and have some "done-reading" signal, after which you stop the
pipeline and get the tags from the tagsink. If you use fakesink, youll
just connect to the "found-tag" signal on the pipeline which should give
you the tags, too.

Hm, I hope that was clearer... :)

Benjamin