How many horizontal lines does a video frame in a standard 720p format contain?

A standard 720p video format, also known as HD (High Definition), consists of 1280 pixels in width and 720 pixels in height. The "720" in the term "720p" specifically refers to the vertical resolution of the video, indicating that there are 720 horizontal lines of pixels that make up each frame. This means that the frame is constructed with these 720 horizontal lines arranged from the top to the bottom of the image.

In contrast, the other listed numbers (960, 1080, and 1440) correspond to different video resolutions or formats. For example, 1080p is commonly associated with Full HD resolution and contains 1080 horizontal lines, while 1440p represents a higher resolution known as QHD, consisting of 1440 horizontal lines. Therefore, the correct answer reflects the defining characteristic of the 720p format specifically, emphasizing the importance of recognizing the resolution as it relates to the number of horizontal lines per frame.