Represents a collection of TimelineMarker objects.
Cannot be used in XAML
You cannot set the TimelineMarkerCollection in initial XAML, or with the XAML used for CreateFromXAML. Instead, you either embed the timeline markers in the media itself, or add them with script after the media is opened, as described in Media Overview.
Changing the collection with script does not affect the embedded markers that exist in the media file, it only adjusts the current MediaElement representation of the collection of timeline markers.