Change variable name
Change method of calculating new duration
Simplify manipulating of AVMutableComposition
Change calculating outputFrameDuration from using minFrameDuration to using nominalFrameRate

Because minFrameDuration is not accurate on some movies.
Change method to checking outputFrameDuration is lower than minFrameDuration

Respect for AVAssetTrack.naturalTimeScale
Using CMTIME_COMPARE_INLINE() macro
Merge branch 'develop'

* develop:
  Change method to checking outputFrameDuration is lower than minFrameDuration
  Change calculating outputFrameDuration from using minFrameDuration to using nominalFrameRate
  Simplify manipulating of AVMutableComposition
  Change method of calculating new duration
  Change variable name