The code below works, but requires an extra copying step that delays the start of play.
B4X:
Dim in As InputStream = Storage.OpenInputStream(f)
Dim out As OutputStream = File.OpenOutput(File.DirInternal, "temp", False)
File.Copy2(in, out)
out.Close
player1.Pause
sources.Clear
sources.Add(player1.CreateFileSource(File.DirInternal, "temp"))
player1.Prepare(player1.CreateListSource(sources))
Sleep(100)
player1.Volume = .8
ListView1.Visible = False
SimpleExoPlayerView1.Visible = True
SimpleExoPlayerView1.ControllerTimeout = -1
SimpleExoPlayerView1.Player = player1
player1.Play