Proposal: generalize playlist concept - short version with pics

[Pavel Shved]

Hi again.

Thanks to Bart and Mark for help and forcing me to reword the proposal.

***

As many developers noticed, what actually amarok plays is a queue of
tracks.  But the playlist is an array of tracks.  The array concept does
support random jumping here and there, but the queue concept does not.

This concept clash leads to many hacks and lack of logic in development
and visualization of such features as random track/album selection,
queuing, `stop after'--with support of properly handling "Previous
track" button pressing.

One part of proposal is to make amarok play Queue instead of Playlist,
the Queue being painted in separate window/widget and allowing
interaction with user (i.e. enqueue track by explicitly dragging it to
Queue widget ).  Tracks are pushed to Queue from Playlist
(sequental/random playback of static playlist) or from Collection
(dynamic playlist).  This proposal is not new and had been discussed
already.

(the following, i believe, is my original proposal)

It's fairly obvious that Queue contains the same items that Playlist
does.  We can note that--as containers--these concepts do not differ at
all.  The only difference is that amarok picks new tracks from singleton
Queue and something else pushed tracks to this Queue from other locations.

The way how it pushes tracks to Queue is going to be visualized via
selection in menu or toolbar: as `random' option being selected, for
example.  I propose to rework it:  we'll add an item to the end of queue
instead; like that:

Queue:
+-----------------------------+
|     Track 1                 |
+-----------------------------+
|>>>  Track 2                 |  <--- currently playing
+-----------------------------+
|     Track 3                 |  <--- next track picked via factory
+-----------------------------+
| +++ Pick random track from  |  <--- special `factory' track.
| +++ playlist  (97 left)     |
+-----------------------------+

When Track 2 finishes playing, amarok starts playing next track from
queue.  It also takes one track from factory for user's convinience:

Queue:
+-----------------------------+
|     Track 2                 |
+-----------------------------+
| >>> Track 3                 |  <--- now playing this
+-----------------------------+
|     Track 4                 |
+-----------------------------+
| +++ Pick random track from  |  <--- special `factory' track.
| +++ playlist  (96 left)     |
+-----------------------------+

At the end, after factory yields its last track, it disappears and
playback stops.

We can introduce several factory tracks:
1) Pick random track from playlist;
2) Pick next track from playlist;
3) Pick track from collection according to bias;
4) Pick next track from playlist according to bias;
5) (Pick no track and) Force playback stop.

But now we can notice that Queue doesnt have to contain only one factory
track!  So we can set Queue to pick 100 tracks from playlist and then
play whole collection, press play and enjoy.

Queue:
+-----------------------------+
| >>> Track 1                 |  <--- picked from playlist by factory
+-----------------------------+
| +++ Pick random track from  |  <--- special `factory' track.
| +++ playlist  (99 left)     |
+-----------------------------+
| +++ Pick random track from  |  <--- another special `factory' track.
| +++ collection (infinitely) |
+-----------------------------+

With ability to customize factory upon clicking it, it will allow users
to have nice visualization of what is going to be played and control of
it; programmers will have cleaner concepts.

By the way, couple of paragraphs ago i said that Queue and Playlist
contain same items.  Playlists can contain factory tracks as well.

Other features are useful.  For example, party mode:
Queue:
+-----------------------------+
| >>> Track 1                 |  <--- picked by factory
+-----------------------------+
| +++ BIAS:                   |  <--- special `factory' track.
| +++ 50% from Playlist 1     |
| +++ 50% from Playlist 2     |
| +++ (199 tracks left)       |
+-----------------------------+

For futher details, why it's cool, as well as for other details, refer
to ADHD version in one of previous threads.  Queue is called genlist or
`generalized playlist' there.

Pavel.