Snap promoted its "YouTube HD Verified" status last year:
http://business.snap.net.nz/snap-becomes-youtube-hd-verified/
13 June 2014 – Snap, one of New Zealand’s fastest growing telecommunications providers, has received the highest rating in Google’s first Video Quality Report in New Zealand. Snap’s network is now ‘YouTube HD Verified’ on average across New Zealand, meaning users can expect to watch YouTube videos in HD (at least 720p) with quick load times at least 90 percent of the time.
Unfortunately, Google / YouTube now appear to disagree. When watching YouTube videos using Snap, it is not uncommon to see a little blue dialog appearing below the video frame, with a vague message about 'interruptions'. Following the link provided, one finds an advisory from YouTube that Snap is rated as "Standard Definition" only.
https://www.google.com/get/videoqualityreport/?v=AQBAf-zF78k
Snap Internet in Auckland
Standard Definition
Users on networks rated as Standard Definition should expect smooth playback on standard-definition YouTube videos (360p) and may experience occasional interruptions on high-definition YouTube videos (720p and above).
YouTube provides a comparison of popular competitor networks. A number of others remain "HD Verifed".