it depends on what the file format is....you will not get much compression with a .mpg file but with a .avi file you will get more. that's because .mpg files are a compressed type of file and .avi files have minimal compression. .mpg files will play on both win and mac platforms but .avi files will only play on windows platforms (i think).
I use WinRAR, WinZip or Quarterdeck Zip-It for compression/decompression.

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