Get asset by extension or mime type? Is it possible to query assets by it's filetype? 

Example: I have a generic asset field, but I want to get the first asset that's an .mp4 file.
To get all .mp4 files:

{% set mp4s = craft.assets.filename('*.mp4').find() %}


To get the first .mp4:

{% set mp4 = craft.assets.filename('*.mp4').first() %}