is there a way to show a layer when video starts?

Any chance you can post the storyline file here, or a storyline file only containing this video and layer? If not, could you elaborate more on the details, such as how you have inserted the video (for example, using a web object to link from YouTube, importing an MP4 etc.) and what this layer contains? 

Is it crucial that it appears the moment the video starts?

Without these details though, my first thought was to use a button/hotspot with two triggers. Play Media - the video, and Show layer - the layer you wish to show. 

Another route is to have both the video, and the content from this layer, on a layer together and set the video to play when timeline starts. Then have a button/hotspot that shows this layer. 

If neither of these methods work for you, then more info would be useful

Hi,

You could do something like this:

Have an object on the timeline which is aligned to the start of the video. This 'object X' has 2 triggers one to show a layer the other to pause media both happen on timeline start for 'object X'. This way as the video starts in the timeline it is paused and you have a layer to say whatever is needed.

This layer should have a button which plays media and hides the layer.

This should work. However video should work on mobile devices anyway have you considered using a web object or something similar to run the video through?