This refers to the specific method of compressing the video file. Some of the above filetypes have a single codec, while others give you a choice. Some codecs are better at certain types of video than others. Compression Digital video requires a huge amount of data.
Digital compression uses various techniques to get acceptable image quality in a smaller package.
The frame size or frame rate can be reduced, or redundant information discarded. Generally the more the file is compressed the lower the final quality will be. This refers to the amount of data required in a specific time. So it's important to be careful with our terms. This is the number of pictures in each second.