Audio tracks and Timed meta data tracks are 0 in uwp mediaplaybackitem

I am using this library in my uwp project. And I am using MediaPlayerElement to play the media, just like in sample of this repo, the only thing I changed is I amusing MediaPlaybackItem to set the source instead of MediaSource directly

var source = MediaSource.CreateFromMediaStreamSource(mss);
var item = new MediaPlaybackItem(source);
ViewModel.PlaybackSource = item;

this media playback item object should have audio tracks for this specific file, and also closed caption tracks represented as TimedMetaDataTracks. But using break point I know the count of them is 0. Meanwhile if I play that file with Movies and TV default app of windows 10 they show a button to change the subtitles and to change audio tracks for that file, I wonder why isnt my media player element showing that button? and why is it 0 when I use the breakpoint?

Thanks in advance.

Start by comparing the sample's direct MediaSource path with the MediaSource.CreateFromMediaStreamSource to MediaPlaybackItem path in the UWP MediaPlayerElement setup. Reproduce the report and inspect the MediaPlaybackItem audio and TimedMetaDataTracks counts, along with the related playback controls. Done means the cause of the zero track counts and missing controls is identified and the issue is fixed or clearly documented.