I would like to watch recorded lectures at 1.7x of their original speed.
Which app will allow me to do that?
I can't find any playback app on the iPad with the exact 1.7 ratio...
However, Azul for iPad (app store link) has 1.5 and 1.75 playback ratios. They even say in their site blurb that it's good for fast reviewing of lectures.
Reviews are excellent and integration with Mail and Dropbox is there, as well as a very comprehensive codec list
I built Swift Player for iPhone and iPad that will allow you to change (speed up) the playback speed of video and audio from the device or even directly from websites like YouTube, etc.
You can find out more information on the product's website.
Note: This is a product that I have developed.
VLC will allow you to playback at 1.5x or 2.0x normal speed. Choose "Faster" from the "Playback" menu.
VLC can be downloaded here: http://www.videolan.org/vlc/
Caveat: I've used VLC on the Mac. I haven't tried any of the "VLC" apps in the App Store, so I don't know if they will do want you want on an iPad. Sorry, didn't see the iPad tag at first.