HTML5 media formats were primarily designed to make the media format war come to an end. But, as you know, the devil is in the details and the result of the introduction of the new HTML5 media formats has only increased the level of complexity related to the choice of media formats. More surprisingly, some old and widespread adopted media formats (such as Flash video) are no longer supported by the new HTML5 media elements.
So if you want to use these new elements (audio and video) you must use the new media formats. But what's the support in web browsers?
Here come the problems. There's no substantial cross-browser compatibility among browsers. For unknown reasons, certain browsers support the Theora formats, other the traditional MP4 or MP3 formats and others both (with variations). So web developers are forced to duplicate their code, like so:
<audio controls="controls"> <source src="audio.mp3" /> <source src="audio.ogg" /> </audio>
As HTML5Doctor says:
Although these inconsistencies aren't showstoppers, in order to compete effectively with plugin-based solutions, we believe any HTML5 audio implementation should be consistent across all browsers and match current implementations feature for feature.
The same problems affect the video element, with the additional issue of codec support. We hope that in a not too distant future these problems will be mitigated in the light of a new awareness of the importance of cross-browser interoperability.