How do you convert long videos(between 1 and 3 minutes) into 4chan's tiny 4mb limit? I want to post on /wsg/ with sound enabled. So I don't have the luxury of disabling sound.

I've converted videos using online converters before, and found it difficult to get a mere 30 seconds under the limit without destroying the quality. What's the solution to maintain a decent quality, while getting longer videos?