What audio's involved? If it's just a recording of someones voice you could just use the likes of Soundflower to route the audio into a speech to text application.

Yeh, if it's just the lecturer speaking you might be able to get away with routing the sound through to a speech to text application. Not sure of a good one but once you find one that works just download soundflower from Cycling 74 set that as your output in System Preferences then choose soundflowe as the input in the speech to text app (instead of microphone)

Yeh it's supposed to be very good. But it's also very expensive.

You're running OSX yeh? In sound preferences you can chose what audio device to output your sound to. Normally it runs through the internal speakers or headphone jack, but if you install soundflower (Download Soundflower Cycling 74) You can choose Soundflower as your output device.

This essentially means that your audio is not exiting your computer but is being sent to an application (soundflower) inside your computer. Dictation apps let you select an audio input (which is generally the built in microphone or a microphone inserted in the mic jack, but because you're sending audio to soundflower you can chose that as the dictation apps input device. So it's kinda like your lecturer was speaking right into the dictation app while giving the lecture.

Becuase I'm such a nice person, do send the file.