This extracts the JPEG frames, _found within an `.avi` file bytestream_, likely without the huffman compression tables (though chrome dont care 8-).
Then it base64 encodes each frame, inserting each frame into a dynamic <img> tag to "play the .avi file".
Add in a short display timeout and keep overlaying images, and you have your "video", using <img> tags, like a flip book.