I've installed the Perian addon for Quicktime so it can open .flv files, and then I can save them as .m4v or .mov. I'm trying to make an Applescript to convert from .flv to .m4v automatically by using this tutorial and butchering their example applescript file, which normally converts ChemDraw files (.cdx, .cml, .mol) to .tiff, so that it instead uses Quicktime to save the .flv files as .m4v. When I try to use it, though, I get an error "QuickTime Player got an error: document 1 doesn't understand the save message". My save message is currently:

save first document in target_path as ".m4v"

which looks like the QuickTime dictionary's instructions:

save specifier : The document(s) or window(s) to save.

[as saveable file format] : The file format to use.

I've also tried "m4v", without the period, and still get the error.
Is my Save direction wrong, or is it probably an error from trying to use Quicktime instead of the original ChemDraw? I tried to change references to .cdx, .cml, .mol, .tiff, and ChemDraw to .flv, .m4v, and QuickTime respectively, but maybe it's more complicated than that?