How to understand sample rate in case of images, it is clear to me when we are talking about the audio, but how these two are related? Is it more complex than the audio sampling?
Sample rates in videos can be seen by how many intervals of... well, samples it takes in one particular time period. The chart and picture below is a good demonstration of this. It's very similar on how it works with audio as well.
In calculus, you talk about the definition of integration by drawing rectangles under a curve and taking the area under that curve. However, if you make the width of the rectangles smaller, you're able to fit more rectangles under the graph and the area under the curve will be more accurate. This is true for sampling as well. The more samples you have in a given time period, the higher and cleaner quality you'll see in the video and pictures.