I tried to use this, but it looks like they have to review me for access.
I've tried the IBM and Google transcription APIs on a podcast with overlapping speakers, and they turned out dadaist poetry. I've been meaning to check out other solutions.
* Google: http://mefiwiki.com/wiki/Podcast_107_Transcript_(automated)
* IBM Watson: http://mefiwiki.com/wiki/Podcast_117_Transcript_(automated)