Lossless compression, as the name implies, means that after compressing the video, and then decompressing it, you wind up with the exact same data as you put in. This is comparable to something like ZIP or RAR (In fact, the most common lossless codec out there, Huffyuv, basically uses the same compression algorithm as ZIP on each frame of video to achieve its compression). Lossless has the advantage that no matter how many times you compress it, you still haven't lost any video data. The bad part is that most often you don't save nearly as much space as you would with other lossy compression algorithms. There are many different lossless codecs these days, each are described later in the guide to making clips.
This is the form of video compression most people are familiar with. 95% of all video codecs out there are lossy, meaning that when you compress the video and then decompress it, you do not get back what you put it. Now, this isn't as bad as it may sound. Obviously if you're compressing something like a text document, you don't want to lose any of the data, but with something like a picture, even if a few bits and pieces aren't quite right, you can still make out the generally gist of the image. Same thing with audio. Famous lossy codecs include MPEG1, MPEG2, MPEG4 (AKA DivX3.11, DivX4/5, XviD, Quicktime MPEG4), DV (and its variants DVCAM, DVCPRO, DVCPRO50, Digital-S, etc), Wiindows Media Video, RealVideo, Sorenson, Indeo, and the classic Cinepak.
Now with that distinction out of the way, we can discuss how to compress the actual video itself, of which there are also 2 basic ways of doing this. These two methods are called intra-frame and inter-frame compression.
Last update: 06:53 AM Tuesday, May 2, 2006