Alternatively, you can record a video of the presentation and post that online, but it's often hard to see the slides. 9Slides combines the best of both worlds, by giving you a way to post both the slides and video in a synchronized and integrated way.
For your online audience, 9Slides is awesome. 9Slides lets people watch your presentation online by showing both video and PowerPoint slides simultaneously. Viewers have a lot of control over the experience; it can play embedded in the Web page or full-screen, and a single button easily switches the video and PowerPoint between side-by-side and picture-in-picture modes (with your choice of video or PowerPoint the larger image). The best part is a timeline at the bottom of the screen that shows where you are in the presentation, displays where slide transitions occur, and lets you skip to any part of the show just by clicking.
On the other hand, uploading the presentation to begin with reveals the site's beta nature. There's virtually no assistance to get you going, and I found that what little help that's there is currently completely wrong. Specifically, the site makes reference to a plug-in which is apparently designed to help you to sync the video and PowerPoint so they play together properly. The site directs you to upload some sort of sync file generated by that plug-in to complete your presentation. In reality, you need to ignore all that. There is no plug-in yet; you instead need to upload the two source files and, after some processing, you're given the opportunity to sync the video and PowerPoint in a Web browser.
Hiccups notwithstanding, 9Slides is worth investigating. The site is indeed in beta, and you'll need to request an invite (which, for me, arrived a day or two after I requested it). You can use the service for free, but the premium upgrades offer more bandwidth, higher video and PowerPoint file size limits, and the ability to view presentations without advertising.
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