Doing a request for the data on an individual video such as:
http://gdata.youtube.com/feeds/api/videos/K-YBQ_at_qU?v=2&alt=jsonc
Used to result in a JSON object that contained a tags property. Has this changed? I’m not currently seeing the property in any videos I request.
I did try searching the changelogs on the reference page, couldn’t spot anything and for obvious reasons “tags” is a fairly common word there.
They are no longer available unless you make the request while authorized using the account that the video belongs to.
This was announced at http://apiblog.youtube.com/2012/08/video-tags-just-for-uploaders.html and the documentation has recently been updated as well.