Look at gstreamer It has a Perl module for the library. It is quite advanced, and thus more complicated to figure out, but it does have a good maillist (where at least the c libs are discussed). That is probably your best bet. If you can get someone there to show a way in c, or with the commandline program, you can probably convert it to Perl.

However, since you already are using ImageMagick to generate the frames(and don't care about sound), I would dig deep into it's docs and examples to find a way with it. IM supports writing to Perl filehandles, in memory images(blobs), and the avi format..... so there may be a way. The problem with IM is the docs are so scattered and unorganized. You may be able to open an animated gif as a blob in memory, write to it, and when done change it's -magick option to avi, then print it. You really have to experiment with IM to get the right combination to work as intended.

I would also look at mencoder (not Perl but it is widely used).