Video playback is limited to MP4 only in 5.9.7

Adding video attachments to pages automatically inserts a multimedia macro, as shown in the first attached screenshot. This is expected.

This macro claims to support AVI, MOV and MP4 playback.

However, I am consistently seeing only MP4 support, with "This plugin is not supported" errors given in Chrome, FF and IE. This is not expected.

I produced my test videos using Camtasia Studio, from the same source recording. My colleagues who are also experiencing this have produced their AVI videos using a different process. We are all seeing the same thing.

Chrome is our internally supported browser of choice, and I am as up-to-date as I can be on Version 51.0.2704.29 beta-m (64-bit).