What is the difference between an avi and an AVI file?

Answer 1

Types

• AVI, or Audio Video Interleave, is a format developed by Microsoft. MPEG is the common term of format standard created by the Moving Picture Experts Group.

Differences

• AVI can be played in most Windows-based applications like Windows Media Player. MPEG works mainly with QuickTime, Apple-based applications and video discs, while MP4 is mostly used with many personal media players like iPod and PSP.

Identification

• MP4 is actually MPEG-4, a subset of of the MPEG standard. What people generally refer to as MPEG is either MPEG-1 or MPEG-2. By contrast, however, MPEG-3 is not MP3, which is included in MPEG-1.

Significance

• MPEG-1 is used with video compact discs (VCDs) while the higher-quality MPEG-2 is used for DVDs.

Benefits

• MP4's biggest difference from the other MPEG formats is its ability to store subtitles, still images and other data along with digital video and audio.

Warning

• Some personal devices may advertise as "MP4 players," using the term colloquially, but actually play AMV files.

Answer 2

nothing, capitalisation doesn't matter in filenames.
But there may be a difference in the codec with two different AVI files.

Capitalization does matter in the filename name extension. It dictates the codec used in the file!

For example (in layman's term) an .avi file contains the codec required to open it in programs such as Windows Movie Maker. Yet .AVI contains a codec that Movie Maker is unfamiliar with.

As such, the file must be 'associated' with a program. Or the file has to be converted for use in the program.