Seems like YouTube has decided to change the YT3D tags and options. They have now standardized on side-by-side LR frame-compatible (squished) format. This would be the same as broadcast, and thus stick with a standard format. It will also mean most modern 3D HDTVs will be able to play embedded YouTube videos. However, this means that all of the videos that were uploaded at full resolution are no longer supported and look messed up. This is because they straight-up DROPPED support for ALL the old YT3D tags (although the videos will still display as 3D, but they might not look right). You can see the new tags and the new rules here:

http://www.google.com/support/youtube/b ... wer=157640

This is most problematic for full-res SBS 720P or 1080P content. For example, look at one of my recent videos which was uploaded as 2560 x 720:

http://www.youtube.com/watch?v=NuoGMBv7pl0

Not looking so good. Fortunately most of my old videos were in the frame-compatible format, so they still look alright. But this a huge blunder on their part. There are a lot of YT3D videos from the past 2 years, who knows what different options or aspect-ratios people were using. And this basically KILLS all that content (including some of my own). I could, of course, re-upload the videos but that sucks. What about all the thousands of views I have, and the comments. I'm just going to lose that. Some people's videos have tens of thousands, even hundreds of thousands views. Are they just expected to throw that away? I don't understand why they couldn't have left in some legacy support (like if the video was uploaded before the cut-off date it would still work). Why do this to people? Should we petition or something? How do we fix this?

I don't think that those new tags work well. At least not for me. I always need to use the yt3d:enable=true. The yt3d:enable-LR doesn't work without it. I found out that on my files, setting the yt3d:aspect=32:18 foxes things, but I normally do not use 720p, I use 1080p. Ihope htis helps.

I really think youtube had nothing to do with 720p to start with.

Ever compared a 16.000 kbps container with that sh*t ? I did, the Duke Nukem Forever launch trailer. YT was just way messed up, it actually hurt the aliasing a lot.

And you expect a streaming site that has to deliver it's picture in real time to match a 3x higher bitrate downloaded file ? Seriously... we don't all have fibre connections, Youtube can't provide 10Mbps streaming or too many people would not understand why they have to wait so long to watch their videos.

Anyways, all my videos seem to be working again with the old tags.

The new tag is:
yt3d:enable=LR

And it does work: http://www.youtube.com/watch?v=CpQC0pjZONs

@tritosine: What are you talking about? People have uploaded 4K 3D videos on YouTube and it works fine (you just need to let it buffer, obviously).

Duh, still this "An error occurred, please try again later" when putting the mouse over the 3D button, I guess the problem must be with Google Chrome or my version of the Flash plugin then. I'm at version 10.2.154.12 here, what are yours ?

yes, I can play a Youtube 3D video (like http://www.youtube.com/watch?v=9HpU0MQldTY) in 3D with Nvidia's 3D glasses (they turn on). Much like 3DVision Live (http://www.3dvisionlive.com/3d_video). There is an option for checkerboard on Youtube which my TV uses. What a progress! Congrats Youtube!
(Google Earth also is in 3D)

luckily the old uploaded videos seem to work fine now- used to be they were squished. good that they fixed that.