Any idea why I can't play .AVI files on Quicktime on OS Catalina?

Thanks indeed for responding. However, my partner also has a Macbook Air OS High Sierra and he CAN play .avi video. It's weird.

I ask because we have a wildlife cam set up in our garden. It is a motion censor video-cam taking photos and recording 30 seconds of video. Although I can view the photos from the memory card, I can't play the 30 second videos using Quicktime but my partner can - using Quicktime.

Baffled at the moment.

Again, thank you for that. In that case, am I able to revert (if that's the term) to adding Perian on my own laptop?

Thank you. I've tried VLC and no joy....

This is utterly perplexing. :(