HTML5 Video works everywhere except the iPad / iPhone / iOS devices.
Double check to make sure your video is H.264 encoded. Most other browsers will play other formats, even Safari on OS X via the Quicktime plugin. There are exceptions (notably browsers that require Vorbis), however, most mobile devices at this time require that specific codec.
Building in xcode gives the following error: The identity ‘iPhone Developer’ doesn’t match any valid certificate/private key pair in the default keychain
There is a problem with your certificate file. You will need to request a new one. Log in to the iOS Provisioning Portal and go to Certificates -> Distribution.
xcode build errors:
Unsupported compiler ‘GCC 4.2’ selected for architecture ‘i386’
This can be caused by importing a project for a pre- iOS 5 SDK into a copy of xcode with iOS 5 SDK only.
To fix, click your Project -> Build Settings. Then under Build Options, there is an entry for Compiler for C/C++/Objective-C. Choose Apple LLVM compiler 3.0.
There is a chance this could effect other aspects of your binaries as you are using a new compiler, so YMMV. That being said, it’s so far caused no issues for me.