I've been playing around with different commenting engines on tinyvid.
Currently I use Intense Debate. An example of a video using this comment system is here. I like this service a lot. You can sign on with OpenId, the moderation tools are good and it seems to be generally reliable.
Intense Debate has support for plugins that anyone can write. Potentially I could write a video plugin that allowed embedding <video> into comments for example.
But it does have some issues. Sometimes comments don't seem to appear in the right order. I'll get an email that a comment was left, visit the page, and it's nowhere. Somehow it gets buried amongst other older comments. This started happening when I switched the ordering of the comments to have the most recent comment at the top.
Sometimes, depending on the content of your comment, the engine gets confused and the comment is scrambled. This seems to happen if I edit a comment that has a URL in it. It converts the URL to an HTML <a href/> and when editing and saving seems to reconvert, or do some weirdness with it. I've lost comments through this. Long comments can get silently truncated or trashed.
I set up tinyvid so I can easily add different comment engines and switch them on and off for individual videos for testing. I recently tried js-kit. An example of video with js-kit comments for testing is here.
I like js-kit too. I'm using their 'rating' widget and that seems to work nicely. The comments are ok too. You can sign in with OpenId. But there is some weirdness there. If I sign in using OpenId, leave a comment, then revisit the page later, then the comments don't appear. I have to delete the js-kit cookie to have them appear again.
There is a limit to the size of the comments, similar in size to Intense Debate's, of 3,000 characters. I suspect this limit isn't a problem in practice however.
There's a lot to like about js-kit, apart from the OpenId issue, but I need to try it out a bit more to see what other issues it has.
The last one I tried was Disqus. Example here. The Disqus site lets you register using OpenId. However you can't login to leave a comment using OpenId. You must login using a Disqus Id that gets assigned to you when you've registered.
When I registered using OpenId, then tried to login to leave a comment it requested a password. I had to go back to the Disqus site, change my profile to add a password. This seems sub-optimal since the point of me using OpenId is to avoid multiple passwords and accounts.
Disqus requires anonymous posters to leave a valid email address. I couldn't find a way to turn this option off. I'm sure this will just result in people leaving bogus email addresses.
One step of the Disqus setup requires adding a script block to the page that does document.write. This won't work on XHTML sites. And I dislike document.write usage in general. Thankfully this step appears optional. It's for converting marked up items in the page to a comment count.
After leaving a comment Disqus does a full page refresh. This unfortunately results in the video on the page restarting and reloading.
Apart from those issues Disqus seemed quite nice. Simple to set up and configurable.
So the end result is I'm not sure which is best. I'll play around with them for a bit more and get feedback. Are there any other's worth trying?