I believe that exposing a user-facing button to change the resize mode serves a pretty niche use-case (compared to toggling the repeat mode).

It's also likely to be hard to disambguate it visually from a full-screen button (which I suspect is a much more common need) - i.e. what icon would you use?

I think we're unlikely to do this, but I'll leave this open in case it gets further support. Our UI components are not designed to serve every possible use-case, they're intended to work for common playback scenarios and serve as the starting point for people to implement their own UIs that can be customised to their needs (possibly by forking our components): https://exoplayer.dev/ui-components.html#further-customization

fair enough..
I just figured it would make sense to provide UI elements for all possible features,
which are (mostly) disabled by default..
and an easy way for the developer to cherry pick which UI elements/features to enable.

with respect to icons that could be used for this particular feature (ie: resize modes)..
I just did a super quick Google image search,
and found a few (with open-source licenses) to share as examples of what I had in mind..

• fill:
  
• width:
  
• height:
  
• harder to iconify:
  • fit
  • zoom

a little off-topic..
but relating to resize modes..

I recently added the ability to my player for the user to dynamically change this mode..
and observed very inconsitent behavior for this feature..
so I figured I'd quickly ask if this is (never-the-less) the expected behavior:

• when the video currently playing is mp4:
  • all modes work as expected
• when the video currently playing is hls or dash.. or pretty much any other video format:
  • cycling through the resize modes produces absolutely no visual change