Video from Prime must have Flash player?

I have loaded a video to Prime and viewed it as learner. Before the video starts I am asked to allow Flash. As I allow, the video shows perfectly (good job with the streaming server ).

Why does the video need Flash ?

I loaded the video as MP4 and thought Prime only allows HTML and many users do not allow, or update Flash anymore. So, Flash should not be needed, or --?

Thank you