Usually I would read the reference in the answer, and edit the answer myself to make it match our standards:
- To demonstrate what our standards are
- To make it easier for the new person who answers
In this case, though, the link is to an hour-long video (so not something I can read, something that would take me more than a hour to listen to), and on a topic which doesn't interested me ... so I don't want to watch the video.
I could read the "Aganna suthra" again though, and summarize that (but I'm still not very interested in the topic, so I might not do a good job of answering, and I don't intend to do that).
Another very good option is, if you think the answer could be better, add your own better answer to the topic.
To ask the author to remedy their answer, you could post a comment under the answer, to:
- Ask that they provide a summary in the answer
- Explain why
If you're looking for an explanation of some/any policy, good places to look for the explanation include:
As for moderating these answers, my moderation policy for answers is more-or-less defined by the answers to the meta-topic, Moderating answers which don't answer the question? -- i.e. an answer is permitted (not deleted) until or unless other users downvote it.
I might (very occasionally) moderate an answer for other reasons (e.g. if it seems to be hostile or off-topic), even without other users complaining about it; but I currently don't delete "low-quality" answers (e.g. link-only answers, or very short opinion-like answers), because I think the community has said that it doesn't want the moderators to do that.
There are, for example, a lot of answers on this site which are relatively "low quality" in having had no upvotes at all (but these aren't deleted). The answer you liked to in the OP currently has one upvote (so presumably at least one person found it helpful, or better than nothing, to be encouraged).