Describe the bug
there are weird issues with the mediatag demo code in www/mediatag

while the embedding functionality using the obfuscated common/media-tag-nacl.min.js seems to work correctly (see issue #842 , the code in www/mediatag is behaving strange.

Aside from

1. the incomplete html document in mediatag/index.html which has no closing </body> and </html> tags
2. the hardcoded blob references in index.html which are not present in most cryptpad instances

There are some more obscure issues. For example the first loaded media-tag always fails with a
Not a media-tag! error reported to the javascript console, followed by several:
Uncaught TypeError: el is undefined

Where did it happen?
The issue is only fully reproducible on third party instances. On cryptpad.fr the media-tag page is not reporting errors, but its not displaying any media tags either

To Reproduce
Steps to reproduce the behavior:

1. edit mediatag/index.html and insert a valid media-tag reference within a local cryptpad instance
2. browse to /mediatag in the instance
3. See error

Expected behavior
The mediatags should be displayed, and the demo-code should be in a working state.

Cryptpad version:
staging (commit e83385c)

Browser:

• OS: Ubuntu 18
• Browser: Happens both with Firefox and Chromium

Screenshot