Audio and video lectures are much less annoying when you play them faster - I find I'm able to listen to most video content at 2.5-3 times normal speed, and most audio at about twice normal speed, both with increased retention (I get less bored, so my mind wanders less).

A couple of time-saving hacks related to speeding up audio or video lectures:

1. QuickTime is great at tempo shifting video and audio to play it back faster without shifting the pitch ("chipmunking"). Look for QuickTime's A/V controls, and "Playback speed". You have to be sitting at your computer to use this, which brings me to…

2. If you use a portable media player, PodShifter will shift (speedup without chipmunking) podcast feeds. If your audio isn't in a feed, HuffDuffer will make individual online media files into a feed, to which you can subscribe using PodShifter. PodShifter is free to use. (I have a financial interest in PodShifter, but this comment doesn't feel spammy to me - please downvote it if you disagree.)

The open source Soundtouch library includes soundstretch, which can do audio tempo shifting locally. Audacity can also do local shifting (look for Effects > Tempo shift).