Add media item with start position

[sampengilly]

Use case description

A podcasting app, where listening position is remembered on individual episodes. If the user starts playback of an episode we queue up other episodes in the same program, if one of those episodes in the queue has been listened part way through, we should resume from that point when that episode is reached.

Proposed solution

There's already an overload of Player::setMediaItems which takes a startPositionMs to apply to the first item in the list of media items. Would it be possible to associate a startPositionMs with the other items in the list, or to have an overload of addMediaItem which takes a startPositionMs? In our implementation we're already remembering the listening progress, we just need to command the player to resume from that point.

Alternatives considered

The workaround I see would be to attach a listener to the player which intercepts onMediaItemTransition events, performs a lookup for the tracked progress and calls seekTo.

[icbaker]

This looks like a duplicate of google/ExoPlayer#6373