I've been uploading my 3D videos to YouTube. YT actually does a fairly good job of supporting 3D. 

But if you use the 16:9 aspect ratio, YT has a bug that will really annoy you.

To enable the the 3D support for a video you uploaded, you would specify two tags:


But you will find that YT will actually display the video at what looks like 16:4.5.....all stretched out and squashed.

So I upload them at 16:9....and then once they are uploaded, I change the aspect ratio to 32:18 (which is just 16:9 times 2). 

This works fine. It may be OK to upload them at 32:18.....I'll have to test it. 

What also looks not too bad is 15.99:9 or 1.778:1...but these are approximations, however close, whereas 32:18 is the most exact ratio. 

Here is a sample 3D vid in side-by-side, cross-eyed stereo: