Best video dictation process?

[tuqqer]

Aside from speaking to Siri on my phone, I've never had a need to use any auto dictation software or process. I now have two long YouTube videos that I need to transcribe. Does anyone have the best process to get any online audio down into words? I suspect that buying Dragon is one possibility, but I'm wondering if there's a Siri-type thing built into Yosemite now, or a website that will do it for free.

Anyone with experience in this?

Always, many thanks.