This (they recently added videos, too).
Alternatively, you can AirPlay videos from the Synology to your Apple TV if you have MKVs.
That is ridiculous. That is not accessing them from your AppleTV. lol. The Synology is a fantastic NAS, storage solution, etc. But it's a horrible idea as a foundation of a media server. Just plain horrible. Simply no way to justify it.
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You.. did not read that, did you?
You copy your files to the Synology and can access them with your Mac or Apple TV afterwards.
Wrong. Do not speak to me condescendingly simply because you are absolutely wrong and do not understand what the Synology does. If you copy files to your Synology, you absolutely can NOT access them from AppleTV unless you have iTunes running actively on one of your computers in your home network. Period. (or if you have an app running on your iOS device and stream them to the AppleTV - which is, again, a horrible and kludgy solution.) That is a massive shortcoming of the Synology unit.