[Update 10/29/14] We found a solution to this problem. For more information visit http://blog.movableink.com/the-solution-to-ios-8s-video-problem/
Just ahead of the iPhone 6 launch last week, Apple rolled out the latest version of its mobile operating system, iOS 8. The release brought a number of great new features, but it also contained a few bugs.
We’ve conducted some testing on the Mail app in iOS 8 and have identified that HTML5 video is not functioning as expected. Videos appear as a poster image with a play button, but when you tap the button, the video doesn’t play.
All other versions of iOS continue to play video correctly, and as of today, only about 7% of all email opens have been from recipients using iOS 8.
In the meantime, our developers are working to identify any possible workarounds that could be applied from our side to resolve the issue.
Check back with us as we’ll post updates soon as we have more information.