How to Combine different resolutions
Choose a resolution
On your iOS device, go to Settings > Camera > Record Video. The default 1080p HD at 30fps balances high-quality footage without filling up your cell. 1080p HD at 60fps creates larger files, but with smoother-looking motion.
Compose your clip
Use a tripod, such as the Manfrotto Pixi mini with a phone clamp (pictured). As well as producing stable footage, a tripod will help you check how the image is composed. This can lead to more professional-looking clips.
Capture some clips
Feel free to change the resolution when capturing different subjects. A 4K size will suit wide shots, as you can zoom into specific subjects while preserving quality. Drop to 720p HD if you run short of storage space.
Slow motion settings
To capture moving subjects — for example, billowing steam — in a creative way, go to Settings > Camera > Record Slo-mo. 720p HD at 240fps will capture a very smooth and slow version of any fast-moving subject.
In iMovie on your Mac, click iMovie Library; choose File > New Event and name the event. Connect your iPhone to your Mac using its USB cable. Go to File > Import Media, browse to your iPhone, then choose Import All.
Create a new movie
The clips will be imported from the iPhone. Slo-mo clips are indicated by a circular icon (at the top left of their thumbnails). Click Projects (top left), then Create New and choose Movie. A new timeline will appear.
Set project size
The clips in your event will be of various resolutions. Drag a 1080p HD video from the Media Browser into the timeline. Afterwards, click Settings (under the Viewer) to confirm the project is 1080p — see Genius Tip, top right.
Clips you add to the timeline will be scaled to 1080p. 720p slo-mo clips might look a little soft due to them being upscaled to 1080p. 4K clips will look sharp, even if you zoom into them manually or apply the Ken Burns effect.