What is compression that I keep hearing about?

[magomago]

A lot of you talk about compression...is this compressing the video like a zipfile or is this just having a lower bitrate? I'm wondering b/c I have a beefy pc and I wouldn't have to worry about having enough cpu horsepower to uncompress it as it is playing.

Ja ne

[TelemachusMH]

Compressing the video isn't done because of CPU usage, but because of hard drive space. A DVD uncoressed into a raw avi would amount to around 1 gigabyte per minute of video. We compress the video so that it won't take up so much space. It is similar in concept to zip compression, however there is a major difference between the two. Zip compression is lossless, and video compression (of almost all types) is lossy. A lossless compression means that given a length of data, that is then compressed and uncompressed, you will have exactly the same thing as when you started. However, with lossy compression the uncompressed output is not the same as the input.

If you took a video clip, and compressed it at a low bitrate, then uncompressed it. The clips would not be the same, but hopefully if we've done our jobs well, they look very similar to the naked eye. After a video has been compressed the data that made up the original clip is not stored in the output anymore. There is NO way to convert back to the original.

TelemachusMH