Você está usando o pacote de movimento que suporta o MMAL? De acordo com este tópico intitulado: Motion / MMAL / Jessie parece que o Pi simplesmente não consegue lidar com a taxa de quadros.
Your resolution question is a bit more complicated. The clever part of this version of motion is that the Pi's camera feeds low resolution video to the motion detection algorithm - so that the Pi's processor isn't too heavily loaded - and at the same time, higher resolution stills and videos of the detected movement can be saved. So you need to have a good look at your config file to get the resolution you want. These are the key lines in the config
O exemplo config mostra o framerate de 4:
width 320
height 188
framerate 4
mmalcam_secondary_buffer_upscale 5
pre_capture 4
output_both_pictures on
output_secondary_pictures on
target_dir /run/shm
snapshot_filename lastsnap
picture_filename preview
movie_filename %Y%m%d%H%M%S
NOTA: A distro usada acima é o Raspian.
Além disso, esse comentário também é importante:
You should be getting the video at 640x480 and the stills at 2560x1920.
Existe outro link sobre como configurar o MMAL - Re: Motion - câmera MMAL .