Do you or anyone else have a simple HTML page that plays .ismv? I can use that as a basis to configure the HTML template. My guess is Silverlight is required, but that shouldn't be a problem because GSP uses Silverlight for other file types.

Even if renaming a mp4 file to ismv worked, I wouldn't ship GSP with the ismv file support included unless I can do a real test with IIS smooth streaming. I may do that someday, but I have higher priorities for now.

Meanwhile, you can do this yourself if you want, since all you have to do is a couple edits to galleryserverpro.config. (1) Add the .ismv mime type. (2) Add an HTML template in the mediaObject section (based on a copy of the video/mp4 template).

You might google this a bit more before firing up your encoder. I found this post that talked about buffering not working for H.264 in Flash until the video was encoded a bit differently. Maybe something similar is true with Silverlight?

I couldn't find a definitive answer on whether progressive downloading of H.264 is supported in Silverlight but I only searched for 5 minutes.