iphone 5s slow motion: Halloween night fireworks

Using iphone 5s slow motion to take Halloween night fireworks
Video:  iphone 5s slow motion: Halloween night fireworks

Below is how I make this video:
1)Take video using iphone 5s slow motion. Export slow motion to local computer
2) Use Windows live movie maker in Windows 7,
edit -speed 0.5x (0.25x too slow)
3) Export the movie in 720p
4) The drawback of slow motion has no sound