Use college YouTube account to load videos. YouTube has a synchronized captioning feature built in. It gets the majority of the speaking captioned, however, you may need to edit parts that it misses.

Sample YouTube video with captioning

http://youtu.be/GwSJW2lSCPk

Use equivalent text alternative documents that students can download or open and read while also looking at the video. This is not as good an option, but it can work.

Sample Text Equivalent Document(s) for the above video

Sample Script
Sample Transcript with slide number and time intervals

YouTube Captioning Tutorials

Creating subtitles and closed captions (https://youtu.be/LCZ-cxfxzvk) - Overview of how to captioning using YouTube.

Automatic timing and transcripts (https://youtu.be/CfuchTRTLGU) - Add a transcript and timing it.

Shared Captioning (https://youtu.be/b9cKgwnFIAw) - Allowing the YouTube community to help you get your captioning done, or helping others do captioning.