To get a good answer to this question (and if you want to understand computer based video) you’re going to need to look up the difference between container formats and codecs. There’s a fairly good starter article here but in summary:
AVI is a Container Format. It defines how the audio and video work together but it is not a codec.
*.avi’s can be encoded with H.264, xvid, divx, mpeg etc etc – yet still retain an .avi extension. To read such a file programs must be able to understand both the container and the codec or they won’t work.
Because of all this, no-one here can say what your file is encoded with, based on knowing the avi extension. AE or WMP might say somewhere what codec is used, if not there are many freeware tools out there that will help.
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