Sometimes Sandvox stalls when uploading/publishing large movie files.
If you are using MobileMe, you can upload the movies using the Finder and link to them from Sandvox.
My example site (with very short movies) is here: [Video-iDisk]
To upload the video using the Finder
If you have already published you site to MobileMe, the Finder path to where Sandvox places movie files is:
iDisk : Web : Sites : SiteFolderName : _Media
Click on iDisk under Devices in the Finder.
1. You can upload your movie to the _Media folder of your published site.
2. In Sandvox you can create a video page
3. In the Inspector, to the right of 'Movie Source:' click the pop-up menu and choose 'From URL' and type in the URL to the movie e.g.
http://web.me.com/username/sitename/_Media/videoname.mov

(it's a good idea not to have space characters in file name to be used on web.me.com, also filenames are case-sensitive in URLs from web.me.com so I keep them all lower-case letters)
4. A grey place holder will appear which will be replaced by the movie when you publish the site.
The advantage of doing this is that publishing the site becomes much quicker especially when doing a Site > Publish All
Tip: I have found that sometimes when publishing to MobileMe, on the first publish the file don't go up, I click publish a second time and they do.
MobileMe from Europe has been very slow to deal with.
