Flash Video Player to play MP4 files for Web

You cannot play mpeg1 or mp4 directly in flash - you need to convert it to flv format.

Well, Flash does not natively handle the AVI container format. It can only play back the two forms of FLVs (Soresen Spark and ON2 v6) and h264 video in a few different containers (MP4, MOV) that conform to some specific requirements.

As far as I know, no one has ported AVI reading code to ActionScript. Technically it should be possible, but there's a good chance Flash simply wouldn't be fast to handle video of any real quality.

You can transcode AVIs to formats that Flash can playback using a variety of tools including ffmpeg.