What file or files can be reduced to the size of the files?

compress

You can resize the image (using any resize tools - look for example at question linked in the reference). For GIFs you have also some other options: - compressing the image (if it is not...

Depends on bit rate, resolution and length of file. H264, DIVX and XVID generally have smaller file sizes for comparable quality.

Any file larger than 999 bytes would have a kilobyte file size.

The size of a file would be limited by the available memory on your computer.