Alfresco should be capable of previewing default supported video formats in each browser. The supported matrix can be found here:
What we've tests in Alfresco 4.0 so far is :
FF: correct (supports OGG and WebM)
Chorme : correct (all of them worked)
IE9: correct (mp4 supported)
Safari : not correct (mp4 should be supported at least) and if Installing QuickTime, Webm should be supported too.
Steps to reproduce
1. Downloaded and install Alfresco Enterprise 4.0.
by commenting out all other previewers based on Flash and leave only the Video previewer (this allows Share to only play videos using the <video> tag).
3. Upload a mp4 or webm video file, which Safari 5.1.3 supports, to the Alfresco repository.
4. Click on the file link to preview and play it in Share in the browser.
Video plays in the HTML5 enabled Safari browser 5.1.3.
Video could not be played (just returned a blank screen) in the HTML5 enabled Safari browser 5.1.3.
However we did find this works in the old Alfresco Explorer (the Web Client). We could run the following video in Safari straight out of the Alfresco repository:
So this is a Share specific issue.