Not sure if you’ve worked this out, but all QT DV movies have the “high quality” setting turned off when they are created. This is a legacy setting so that DV movies could play on a mac without overloading the CPU. This is unnecessary with modern cpus.
Simply open up any DV movie – select cmd-J and then video properties. At the bottom right of the dialog box, check the High Quality button. This setting only affects the way a file plays on a computer monitor, and has no affect on the file itself or in conjunction with tape layback etc.
good luck