New metadata are needed to describe 3D methods.
HDMI 1.4a provides new descriptors in the vendor specific infoframe for 3D types support : side-by-side, top-over-bottom, frame-packing... half or full... (see http://www.hdmi.org/manufacturer/hdmi_1_4/3d.aspx)
Specification for Stereoscopic Windows Media Files v0.2 is also moving ahead (see http://www.3dtv.at/knowhow/StereoWmvSpe ... Attributes)
But what about MPEG4 metadata ? Because their are focus mainly on 3D oriented codec, they currently don't propose any metadata for "flat 3D" (I mean for left and right views stitched together or just double streaming).
Then new metadata can not be inserted in tools like FFMPEG without hacking (ok, just modify C and recompile it;)
Any input about new MPEG4 metadata for "flat" 3D ?

Ok, "flat" 3D means stereoscopic

You can easily add meta data to any file. The problem is to have the video player capable of detecting them, recognizing them and then use them correctly when playing such a file.

Peter Wimmer's wmv meta data aren't standard. He intoduced them by himself and added support in his own player but that's it. No other 3D video player uses them.
I wish there were similar metadata for any video (tags attached to the video container for example, the matroska container appears to be very favorable to this kind of approach) but if these aren't used in players they're useless.