Here's some fireworks filmed in slow motion with the iPhone 6, click on the image to see the movie:
The 240 frame per second slow motion video recording on the iPhone 6 is very cool, if you can find a good subject. If you import the video on the Mac you get an extra file that tells Quicktime where the slow motion starts and ends, so Quicktime Player can play it in slow motion. To other software it's just a 240 frame per second movie. If you want to see the slow motion in other players, you need to share through Airdrop from the iPhone to a Mac, then the iPhone will convert the video to 30 frames per second.