Extended shell media controls

We discussed this a bit at the Berlin GNOME Mobile hackfest. The takeaway was that apps have pretty diverse use cases and needs, making it hard to show useful controls without knowing a bit more about the content/context/type of app.

Types of use cases:

• Short video
• Movie
• TV Show with multiple episodes
• Podcast
• Live Stream (audio or video)
• Music
• Voice Message
• Audio Books
• Presentations (MPRIS prev/next buttons)

Some examples of custom layouts on Android 13:

Features:

• Title
• Subtitle
• Album cover
• Jump +10s
• Next/prev track
• Interactive progress bar
• Non-interactive progress bar

Other features apps may want buttons for/have buttons for on other platforms:

• Skip chapter
• Landscape cover for videos
• Add tracks to favorites
• Set 1.5/2x speed
• Interactive seek bar
• Non-interactive progress bar
• Presentation app (e.g. no play button?)
• Buffering state for live stream?
• Record stream?
• Adaptive speed?
• AI skip to beginning of sentence?
• AI skip ad?

Potential approaches:

• Special case specific use cases (music, podcasts, etc.), apps can specify which they want
• Allow apps to specify exactly which buttons they want

Proposal for a path forward we discussed at the hackfest:

• Apps request which of the default buttons they want
  • Pause/Play
  • Next/previous track
  • Skip forward/back (app can specify how many seconds)
• Maybe apps should be able to customize icons for default stuff (e.g. custom icon with skip interval on it?)
• Apps can define custom buttons with custom icons for edge case-y stuff
  • The shell sends an mpris call to the application once a custom button was pressed
• Default stuff like play/pause has to be supported
• Shell defines the precise button layout, but maybe apps can provide layout hints in addition to buttons?