It's true for video recorded by professional cameras, but if you check video recorded by most mobile phones you notice that it's wrong.
It's unfortunate that so many tools assume constant framerate, because VFR is a useful compression technique in itself --- for sequences where there's basically no change between frames (few-second black scenes, for example), the encoder can stop continually encoding "no change" and just wait until there is.
It's unfortunate that so many tools assume constant framerate, because VFR is a useful compression technique in itself --- for sequences where there's basically no change between frames (few-second black scenes, for example), the encoder can stop continually encoding "no change" and just wait until there is.