OpenCV3 ffmpeg has no definition

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I am currently working on installing ROS on a raspberrypi 3 on Stretch. While following the a tutorial I was lead to these instructions on updating the ros_catkin_ws workspace. I had to run the command:

rosdep install --from-paths src --ignore-src --rosdistro kinetic -y

When I do that I get the error:

ERROR: the following packages/stacks could not have their rosdep keys resolved to system dependencies: opencv3: No definition of [ffmpeg] for OS version [stretch] I have been looking around but still have not succeeded in solving this issue. I tried installing ffmpeg separately but that does not eliminate the error. How do I solve this?