Computers compress image and audio data through a process similar to summarising: it analyses the data using algorithms that use brightness and colour instead of RGB values for images, and different frequencies of sound rather than samples at different points in time for audio. These algorithms then discard parts of the information that human senses do not perceive easily, and reduce the resolution of other parts that human senses are not as sensitive to.
Data cannot be compressed beyond its predictability limit (Shannon entropy) in a lossless fashion. Lossless compression does not discard any information. It generally tries to spot patterns in the data, and represent those patterns with fewer bits, through a combination of predictive coding, run-length encoding, and entropy coding.
A video container can hold one or more audio, video, or text data streams. To encode or decode a data stream, you need to have the necessary codec installed[^1]. Most video runs at 25 or 30 fps, with high-quality video going up to 60 fps. You can use a program like MediaInfo to help you decipher the streams inside a video container file.