I am adding a new mimetype for mp4 files to Tridion. I have followed the instructions on the Tridion Live Content site here. (login first).

And I have confirmed my settings match the blog post here.

And then I flushed my browser cache and even restarted the CMS server. But, I still get the following error:

The file extension of the selected item is unknown. The specified file does not match a supported Multimedia Type.

Any ideas?

  • 4
    Did you add it to multimedia schema? Do you get exception when adding MM type or when trying to create MM Component using this MM Type? Jul 16, 2014 at 12:22
  • Yes, this solved it. Somehow I assumed using the default MM schema would use all types, but of course it didn't know about my new type. Please answer and I will mark it as accepted
    – robrtc
    Jul 16, 2014 at 13:31
  • 1
    So the distinction is Multimedia Types can be used in one or more Multimedia Schemas. Jul 16, 2014 at 13:34

1 Answer 1


So, just to post it as an answer, the problem was that newly created multimedia types are not picked up automatically by Multimedia schemas. One should manually add the new MM Types to the proper MM Schemas

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