More interactive queueing system

[toots]

It would be nice to have a queueing system that allows more interactions. The actual queue is very good for all automated systems, but for a manually controled source, it's too limited.

In particular the following controls would be nice:

• Full control over the order
• Ability to check metadata for any request in the queue
• other...

This should not be a replacement for the actual queueing system, but perhaps a different type of queues, aimed at pure manual manipulations.

In particular, theses types of queue could also be used for the MPD playlist (see #131), on top of which you would plug the MPD protocol to interact with it.

[metamorph68]

(In [6614]) Added estimated remaining time in request-driver sources. Allows these sources to fetch less files in advance. Default behaviour now using this, set conservative to false to enable previous behaviour. fixes #169, references #146

[wiki]

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[mrpingouin]

Why not merging request.queue and request.equeue, make equeue more stable (I bet it's not, it's almost unused) and even more flexible? We should decide on that before 1.0, after that we'll have to preserve compatibility.