You can use digital zoom in both live video and archive view modes.
To zoom in, pinch the video with two fingers.
Note
If it is not a PTZ camera, then you can also zoom in by double-tapping on the screen. Video will be zoomed in to x8 size.
Video cannot be made smaller than its original size. You can zoom in up to x8 size.
To select the visible part of the frame when the video is zoomed in, move your finger beyond the video viewing area.