No, such an app would be extremely unsafe. If I have to keep walking to keep the show playing, I'll lose myself in whatever I'm watching and settle into a status quo where I power-walk deliberately along but with increasing detachment from my environment as I focus more and more on my phone.
This type of situation nontrivially raises the chance of tragedy if I decided to use this app in urban areas.
That's how I see it. Maybe your app could catch on in Japan, which offers "texting lanes" (dedicated sections of road for phone users completely lost to their environments) in some areas.
The only way I could see such an app being useful is if you were able to usefully blend the rear camera with the video being played in a way that was nondistracting.