For video the story is the same there is lossy and lossless.
AVI, divx to some extent and others are lossless. As a result are crystal clear at the native resolution.
MPEG, MP4, WMV, and MOV and flash are lossy. IMHO MPEG is the best but there is a good argument for MP4. Flash and WMV crap. MOV (quicktime) is ok but MPEG is the best over all. The question here is codecs which are used to convert the video. Some are better than others. Plus the audio has it's own compression. MP3 is lossy while WAV is lossless and is typically used with AVI.
Basically just convert the video to MPEG. Most MPEG encoder programs uses codecs that let you select the compression level. That level is effectively the amount of quality you will loose.
File compression like zip and rar will work on video but are really most efficient on text not images and especially not video. They still work but the compression just is not as good because they use patterns mostly based on phonemes which are tokenized. Take a plain text file and zip it. Then zip an image of the same size as the text file. The zipped text file will be much smaller.
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