Q: Some Videos are not playing in my 4s

Phone model: i-phone 4s

OS: Current version iOS 8.4.1

I shoot some videos one month back i played at that time it's played well. After few days suddenly those are not playing what is the reason?

I observe one thing, one time when i am in call my daughter open the gallery and try to play some video from that time i am facing this problem it may or may not the relevant to this problem just it's my observation.

Note:-

1. When i was shoot this video the iOS  version is previous of iOS-8.4.1

2. Now my Current version is iOS 8.4.1

3. I have same problem with previous version also