Cosmo Wright has the current world record for beating Ocarina of Time quickly, with a playthrough that clocks in at eighteen minutes and ten seconds. Even if you've watched the incredible near-perfect run before when we initially posted it, it's worth watching through again just to hear his excellent commentary.
Wright explains the history behind this run, including when big glitches and breakthroughs were discovered for Ocarina of Time. It's clear that the current world record is the result of many years of optimization, tinkering, and tons of hard work.
Wright also takes the time to explain many of the tactics used in his run, as well as the rationale behind most of what you see in the video. It's an incredibly informative video, and well-worth watching if you have 25 minutes to spare.