The reason that the "Burst Mode" is so important, is that the 4K videos being captured by Vizzywig 4K are really a series of 4K photographs being shot at 24 images per second. Stitching these photos together creates a 4K video, and allows you to access and edit each individual frame. The app also comes with the ability to create title slides, scrolling credits and transition effects. Audio is recorded separately and synced later with the video.
The developer behind the app, i4software, says that it hopes the iOS 8 "Burst Mode" limit will get fixed in future builds of the OS, which will allow buyers to update to iOS 8. If you're really, really, really that determined to have 4K video capabilities on your iPhone 5s, start reaching for your credit card now.
source: Vizzywig 4K (iOS) via SlashGear