It is the weird behavior of Safari Browser as explained by Johndyer in issue number #536 quoting below:
This is a really frustrating part of safari in that it only happens when quicktime isn't installed. In that case, Safari still acts like it understands HTML5, but it fails in strange ways that I haven't been able to detect. So just install QuickTime adn you'll be all set.
Its is working fine with Quicktime installation.