I would like to use Dictation to transcribe lectures which are in mp4 format. The only input choice I see is microphones. Is there a way to select existing files in mp4 and mp3 format and have Dictation transcribe them?
MacBook Pro with Retina display, Mac OS X (10.0.x)
You can only get Dictation to (attempt) to transcribe your mp4/mp3 audio if you play those audios from a separate device in front of a good quality microphone while dictation is running. You cannot have dictation listening and transcribing to audio concurrently playing on the same machine.
You will want to use the Enhanced dictation capabilities to avoid round trip delays to Apple's servers. Since Dictation gets better over time by recognizing your voice patterns, playing lectures to it, with any injected noise spikes, may be very frustrating for you.
I used the Apple Dictation tool on my iPhone to record the word “testing” four times. When I played this to an external microphone, and OS X dictation listening in Pages v5.2.2, the words were correctly transcribed.
Using Dictation with audio files as input
