Moving Image Education

Compression is a massive field, but it is worth grasping some basics. A video clips file size is dependent on:

• Duration
• Frame size
• Compression
• Frame rate
• Soundtrack

When you compress a film or sequence you are usually making it into a quicktime mov, mpeg or an avi. You might not notice the difference on your computer, but you probably will on a good TV or at a screening. The more you compress something, the smaller the new file becomes, and usually the worse the quality will be.

duration

Film length is something you are unlikely to change at this stage. But if you can and you want a small file size, shortening your programme will help a lot.

frame size

Frame size is the dimensions of the image in screen pixels (horizontal x vertical). Smaller frame sizes mean smaller file sizes.

frame rate

Some live action can look okay at 12fps or even less. With animation you may have created your work on 2s or 3s so you will be able to select a lower (appropriate) frame rate with perfect results (try it out first).

compression

After 'image size' and 'frame rate' the only real way to reduce file size is to compress your image. Compression is the stripping out and simplifying of information to make the file smaller and easier to handle (like a .jpeg when you're dealing with still images). The best option is to run tests to see what is acceptable.

Although people occasionally call miniDV 'uncompressed' it is actually compressed at source (ie when you film) with quite a high ratio of 1:5