I have just downloaded and successfully used this excellent program. It has been created by Ben Smith from Ultrasound of the Week . I used a Mac, there is a Windows version as well.
The avi that my machine outputs was very easily converted into a GIF loop with the ability to trim the length and crop the size of the video. Does exactly what it says on the box in a very easy manner. A great addition if you are saving and using images for teaching. Just don’t forget to confirm consent to use images for teaching/research!