I am working with django 1.6, python 2.7, firefox 30 and Mac OS 10.10 Beta. When I render the following code <video width="570" height="340" controls="controls"> <source src="/some/path/" type="video/mp4" /> </video> I get an error stating "No video with supported format and mime type found". The same code runs perfectly on Safari and Chrome (yes I still haven't checked IE). I have tried different formats for the uploaded files and looked into ad-ons which might prevent this or different coding mechanisms, though nothing has been helpful. Please help!!!!