Currently, we offer an 'Events' function within any Storyboard timeline, that offers the ability to trigger Actions at designated timestamps across a Storyboard.

Among these Event Actions, is the ability to PlayMediaAction.

This function works as expected when a Storyboard is located within a Page.
However, it fails when an equivalent Storyboard is located within a Template.

See repro steps and attached file.

Repro Steps:

1) Download, unzip, and open the attached Studio Project.

Within this Project's MainPage.xaml, you will find the Page divided into two:

On the Page itself, on the left: a Media Element and a TextBlock whose presentation is controlled by a Storyboard found on the Page called 'MyPageStoryboard' and which is triggered to play onLoad. This Storyboard features a Timeline Event to 'PlayMediaAction' targeting the video MediaElement found in the Page.
This Storyboard in-action can be viewed by Playing the Page, and it can be observed that the Text animates in size and colour succesfully, and the video also plays successfully.

On the right of the Page, a ContentControl Element, that within it, contains the two same Elements: a TextBlock, and a video MediaElement.
Within this ContentControl's 'Content' Template, can be found an identical Setup as the one described above at the Page Level:
A Storyboard that plays onLoad, and which animates the TextBlock, and is supposed to 'PlayMediaAction' on the video MediaElement.

2) Play the Page.
Observe how on the left, both the TextBlock animates, and the video plays.
Observe how on the right, only the TextBlock animates.
This gives a clue that the Storyboard within the ContentControl Content Template is triggering properly and playing, and that the issue seems to be moreso about a failure for the 'PlayMediaAction' Timeline Event inside of the Template, to function.

Expected Results: All Timeline Event Actions function within a Template as much as they do on a Page.