HTML5 MP4 Codec Settings for Safari 5.1.5

Hello all,

I am having a problem with HTML4 MP4 h.264 videos in Safari 5.1.5 only running under Lion. Does anyone have any exactly specifications for compressing videos that will play in this version of Safari? Also, if you have sucessfully exported videos for 5.1.5 what software are you using to encode? I have tried several options (After Effects, QT7 etc) and not had any luck. Thank you!