Why is that, to maintain the original quality of an AVI file in a video editing program, the resultant file has to be larger than the original? After all, a copy of a still, JPEG file is the same size and quality as the original.

General Thoughts:

Actually a JPEG file is compressed (if you open a JPEG in Photoshop you can see the actual amount the file size would be without the compression). Mathematical algorithms are used to reduce the amount of info required to display the image and this results in smaller file sizes. It takes away information from the image but is designed to take away information that is not noticable to the average human eye. If you use extreme compression, or recompress a JPEG over and over you will see quality loss.

Video editing programs sometimes have their own compression schemes (like Avid). Sometimes they use what's availabe to them via your system (like QuickTime).

The way your editing program handles imported media is usually controllable through your settings.

Your editing program may use a different codec from what you used in creating the AVI - that has a direct bearing on file size.

Obviously I can't address your specific program. I don't know what it is and even if I did, my knowledge of Windows-based video editing software is limited. But hopefully at least I've given some baseline understanding of some of the relevant factors.

I realize that a JPEG is a compressed file. But the point is that copying it doesn't make it any larger. I should have said any copy of any ordinary file in the same format (TIFF, Word, etc) remains the same size as the original. So why can't I just stitch together two AVIs of say 1.0 Mb each and have a perfect copy with 2 Mbs? I understand the compression options in my video editing program, but why -- to be repetitive -- can't I just retain the original's compression without increasing file size?

Hmmmm. If the clips you're importing have the same frame rate, resolution, data rate, codec settings, and audio characteristics (stereo vs. mono, compression etc.) as the file you output from your editing system, I woud think they would add up (1 + 1 = 2). If those conditions are met and it's not equaling "2", I'm afraid I'll have to plead ignorance and hope someone more familiar with the .AVI format responds. little_dragon, are you out there?

Just passing through. Some video editing utilities pad the video clip with additional "junk", so even if you're using no compression (or lossless compression) and haven't altered the clip, there may be a file-size discrepancy between two otherwise identical videos. My editor-of-choice, VirtualDub, does the opposite; it strips the useless junk out of the video instead, and I typically end up with smaller file-sizes, even on a direct-stream copy with no recompression.

The padded bits are called "junk chunks", by the way.

Thanks, I knew you'd know! [grin]

Yes, I'm an absolute fount of useless trivia .... :)

Many thanks. I'm using VideoWave II. VirtualDub sounds interesting. Tom

It's free, also. Here's a link:

http://www.virtualdub.org/

One reason file size increases could be that compression schemes record the differences between frames. When you edit, at the points where you make an edit, you are changing the differences, often drastically.