[ros-users] Creating movie files at variable framerates

Are there any tools anywhere in the ROS stacks, or does anyone have
any techniques for, generating movie files from a ROS image topic? The
tricky bit is that I have an image that is updated at some variable
rate (usually something like 1 to 5 Hz), and the only ways I know of
to create movie files would assume a fixed constant rate. I want the
movie that is generated to maintain this variable timing, and ideally
well enough that it can be synchronized with other output such as an
rviz display (the latter captured with GLC).

I suppose it should be possible to do a fixed frame rate that is high
relative to the variable rate, say 30 Hz, and just write frames out to
disk at that high rate even if they are unchanged.

But are there ways to do this without most of the output being
duplicate frames? I did some googling around and found hints that
variable frame rate codecs exist but very little information about how
to generate movies.

Thanks,
Pat