ffmpeg **doubled** my duration
By default, ffmpeg treats image sequence and raw video inputs as having a native rate of 25 fps unless told otherwise. So, the -r 50 duplicates each frame.

Use

ffmpeg -framerate 50 -i imageSeq-%06d.png -vcodec png -pix_fmt rgb32 -y video.mov


You can skip the -r 50 since ffmpeg will use the input's framerate.