There is often a difference in the video and photo resolution on the same MP camera because video and photo capture are different processes.
When taking a photo, the camera captures a single still image with a high resolution, whereas when recording a video, the camera needs to capture a series of images (frames) in quick succession to create the illusion of motion. The video resolution, therefore, is determined by the size of each of these individual frames.
Additionally, the aspect ratio can also affect the difference in video and photo resolution. Photos are usually captured in a 4:3 or 3:2 aspect ratio, while videos are often recorded in a widescreen 16:9 aspect ratio. This means that the video resolution may need to be reduced to fit the widescreen aspect ratio, resulting in a lower resolution compared to photos.
Generally, a 20MP camera produces photos with a resolution of 5472 x 3648 pixels, which is a 3:2 aspect ratio. In terms of video resolution, a 20MP camera can record 4K video at 3840 x 2160 pixels or Full HD video at 1920 x 1080 pixels (both 16:9 aspect ratio).