I found instructions on how to put a preview JPEG of the most interesting part of the video, but the instructions are for a Quicktime .MOV file. But my file was originally a .VOB file which I had to convert it to .WMV which didn't work in all browsers, so I converted it to .MP4; the conversion software I found didn't have a setting for Quicktime .MOV (although it had plenty of other Apple video settings). If I follow the instructions for Quicktime, will it likely work with my .MP4 or do I have to find something to convert it to .MOV?

Also, my video is on my page at 720 width and 480 height which worked fine with most browsers when it was WMV, but now that it's MP4, it shrunk to 322 width by 257 height in all browsers except Chrome which didn't show the video at all (tho I haven't tested it in Explorer yet).
I didn't change the size in my code. Why did it shrink? Is that what happens when you convert from WMV to MP4? How can I fix this?