Compare and Contrast "Formats"

That's the short answer. I'm not sure I know the longer answer.

But if you have two videos with different file sizes, but otherwise they are exactly the same when played, then you are left with the reason that they were both encoded differently by different people.

Encoded means "CoDecs", or Compression/Decompression, and this is an absolute minefield. There are so many different codecs that compress the original video file into more manageable file sizes, that people choose to compress with whatever they find is best for them. The compression involves compressing video as well as any audio track, and both aspects have different compression ratios that can be selected at the beginning of the compression process.

So, even a file of the same file type, in your examples AVI, you can get many types of compression, requiring many different codecs in order for the media player to play the file correctly.

But this applies to all video file types, not just AVI, so I return to my original answer, if the video plays correctly and to your satisfaction, there are no reasons why one format is better than any other.

Hope that helps.

Mark

Breaking up the file was needed when folk moved such via NEWS SERVERS.

As to differing encoding, some folk can't play this or that or want it to play on the iPad or such and you may see different resolutions for each encoding.

Here's my suggestion. Use the version that works for you and learn about transcoding with tools like Handbrake.
Bob