https://msdn.microsoft.com/en-in/library/office/dn499819.aspx#bk_WebMapToIcon
This one seems to missing a lot of file types, for examples mp4 and mp3. Where as when viewing these files types via a modern view they are all there.
Modern Library is using following image from a cdn, rather than /_layouts/...
<img class="FileTypeIcon-icon" title="mp4 File" src="https://spoprod-a.akamaihd.net/files/odsp-next-prod_ship-2017-09-01-sts_20170908.001/odsp-media/imag..." style="width:16px;height:16px;" data-reactid=".0.0.0.0.0.1.0.0.0.0.$page-0.$dfb9408b-716a-4afd-8fd7-6a936098bc3c.0.0.2.$0.0.0">
Ideally don't want to have to roll my own just to get some more files supported.
