I cannot open a video "AVI"

I cannot open a video "AVI" because a codec is missing . The following message appears: The document « XXX.HDTV.x264-ASAP.avi » cannot be opened. A requested codec is not available.

I can see the video mp4 on my Mc bookair, but if I want to see on my tv Set I have to convert with Movavi video converter into AVI. The Movavi converts only partly my video into AVI, then I can only my download viedo on my Mc book air. How can I see my downloaded videos on my TV set?