[Playlist] [rfc] Nested playlists (and playlist chains) again

[Sebastian Pipping]

So let's go for the official extension thing.
Here's a tree of doable ways to nest playlists:

 (A) Several files linking to each other
     in an acyclic way.

 (B) One single file containing several
     playlists. Sub-playlist definitions
     and their hierarchy are held at one
     central place in a playlist <extension>.

     (1) Tracks say what playlist(s) they
         belong to.

     (2) Sub-playlists say what tracks
         they contain.

Both approaches have pros and cons and are
needed, the former for infinite playlists/
radio modes when loose coupling is needed
and the latter for fixing a whole player's
state, in general when strong coupling is
wanted.


== Questions for the several files way ==
* What way do we make the official for
  linking to other playlists?

  * Can a playlist go into a track's
    location? Should it?

  * Do we see sub-playlists as a track
    with sub-tracks or not? If not
    a playlist extension would be the right
    place to put it.


== Questions for the single file way ==
* which way to go - (B.1) or (B.2)?

The VLC file I saw today is going for (B.2):

    <extension application="http://www.videolan.org/vlc">
        <node title="mp3">
        <node title="113 - 113 degrés">
            <item href="0" />
            <item href="1" />
            <item href="65" />
        </node>
        <node title="ACDC">
        <node title="Back In Black">
            <item href="66" />
            ...
        </node>
    </extension>

The href attributes point to numbers in identifiers.
Staying close to this approach would ease VLC's future
transition. Or are there bigger design flaws hidden inside
we have to fix? Is scattered information tagged to the tracks
better for some reason?

Let's get something working, let me know what you think :-)



Sebastian