Tuesday, May 11, 2004

I'm seeing a strange problem with QuickTime panoramas that I make with the QuickTime Authoring Studio and then export with fast-start previews using the QuickTime Player: the preview shown while the rest of the movie downloads do not line up with the final movie. I have seen this across multiple versions of the QuickTime software and across multiple machines AND platforms. They appear to be most dramatically mismatched at the wrap-around point (i.e. the edge of the stitched pict file). This affects most of the panoramas on my site. Sometimes the problem seems more visible on PCs than with Macs. At those times, I can get the scenes to preview perfectly on the Mac, yet on the PC the preview is mis-aligned. It happens whether I have the QuickTime Player (pro version) to generate the blurred preview file at one quarter size, or I create a blurred preview image and add it myself. The other funny thing is that not every movie is affected, but it looks like most are. When the problem is evident on the Mac, it seems that the preview image is somehow not being stored properly, as I can open the movie in DeliVRator and see the preview and observe that it is mismatched there. Sometimes the problem seems to go away on the Mac if I choose a 1:1 ratio preview image instead of the 1:2 or 1:4 ratio that I usually specify. However you really pay a size penalty for that option. What appears to be happening is the preview image width is being multiplied by a factor of 1.2 to 2 of what it should be. So the tiles near the initial viewpoint are usually matched right on, but as you pan around, the preview either gets farther out of alignment as you get closer to the "edge", or it flips out completely once you get past the tiles which were loaded for the initial view. What I mean by "edge" is the place on the flat stitched image where the scenery stops and continues on the opposite edge. A perfect example of a scene which works fine on my Mac but the preview is mis-aligned on a PC is Peyto Lake.   This movie was generated by the QuickTime Player using default values for the preview: 1/4 size blurred JPEG. Here are the things I've tried to work-around this problem: * used different bit-depth preview images. Tried 8 or 16 bits, no difference. * used preview images evenly divisable by 96, or 16, or 4. No difference. * used preview images that are 1/4, 1/3, or 1/2 the size of the original pano. No difference. * used a TIFF or Photoshop preview image instead of a PICT file. No difference. * used grayscale or color preview images. No difference. * quit the QT Player after exporting, in case it only happened on subsequent exports. No difference. * tried using a color profile in the saved preview image. No difference. * tried changing the motion quality setting from high to medium. No difference. * tried changing the number of tiles used in an example QuickTime VR movie from 122 to 24, 16, or 12. No difference. * tried changing the number of tiles to 1, 4 or 8, and used a 1:1 or 1:4 ratio preview image for my 5856 pixel wide source image. Seems to work on both PC & Mac. However these are not magic numbers -- 8 tiles failed on another panorama. It appears that less long panos (in the 4000 pixel range) must stick to 1, 2, or 4 tiles. Yet no one else has seemingly reported this problem (last time I checked). How bizarre. Anyone else see this? Any suggestions to work around it? I'd just as soon let QTVRAS pick a number of tiles rather than have to do an experiment to find out how many tiles works for every panorama. I've spent at least 16 hours trying to work around this problem since I first noticed it years ago. 12:00:39 PM

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