Superfly,

   I work for MindTouch, maker of an Enterprise Wiki solution which is also Open Source.  I wanted to put that disclaimer up first.  I'm going to talk in generalities though and not sell you anything.

Almost all wiki software support linking of some sort within the editor.  The question is, do you want it to be a WYSIWYG experience or are you ok with using a markup to link.  Posting videos on the wiki is also something that a majority of wiki software solutions support.  some require plugins to support this and others include built in dialogs that allow you to reference internal and external video files.

As for the upsides and downsides of Commercial vs Non Commercial (by non commercial I believe you are referencing Open Source) wikis, Open Source wikis are typically free from a licensing standpoint and depending on the size of the project, the community can provide helpful resources for setup, configuration, and deployment of your solution.  The downside is that if you want support then it may be hard to find and depending on the solution you pick you will have to have knowledge of server management in order to administer, especially if you want it behind your firewall and not hosted.  With the Commercial solutions, there is the licensing fee, but there is also the benefit of commercial support where you can access a representative of the company in order to help you with configuration, setup, and deployment, along with being able to help you with upgrades. 

Now the nice thing about working at MindTouch is that we have the best of both worlds.  We have a Commercial Solution: MindTouch Enterprise and we have an Open Source solution: MindTouch Core.  Both can be downloaded for Free from our website: http://www.mindtouch.com/Download.  The Enterprise edition has a 15 day trial whereas the Open Source edition is free forever.  There are feature differences which you will be able to see on our website.  I strongly recommend to look at all of the solutions available, compare the features through the matrix on this site, and create an even longer list of requirements.  In this competitive arena you can narrow your solution down to exactly what you want. 

I hope this was fairly general without too many marketing undertones.   If you have any other questions please reply to this forum.

Superfly,

  Our OpenSource software does include a WYSIWYG editor and in fact we store everything as XHTML as opposed to wiki markup to ensure that it is standards compliant.   If you are interested in accessing content on an inhouse server then MindTouch is definitely a solution to take a look at.  The way our framework is setup, it allows you to expose external resource in the MindTouch page like retrieving information from DBs, external applications, and web services.