You can use the QuickTake camera on these devices: iPhone XS, iPhone XR, and later.
Hold the shutter to take a video
To capture a QuickTake video, just press and hold the Shutter button.* Release the button to stop recording.
On an iPhone XS, iPhone XR, and later with iOS 14, you can hold one of the Volume buttons to capture a QuickTake video. If you have Use Volume Up for Burst enabled, you can capture a QuickTake video with the Volume down button.
Slide to the right to lock recording
To keep recording video without having to hold the button, slide the Shutter button to the right, then release it. When video recording is locked, a shutter button appears to the right; tap it to take a still photo during video recording. When you're ready to stop recording, tap the record button.
Slide to the left for burst mode
Slide the Shutter button to the left and hold it to take a burst of photos, then release it to stop.
On an iPhone XS, iPhone XR, and later with iOS 14, you can capture photos in burst mode by pressing the Volume up button. Just go to Settings > Camera and turn on Use Volume Up for Burst.
* To take videos with customizable resolution, stereo audio, and audio zoom, switch to Video mode.