speed up video analyzer

[khoan]

# currently takes a long time
identify -ping -format '%m %w %h' /path/to/video.mp4

can we somehow extract first frame and use it to return format, width and height?

[khoan]

# this runs in seconds
identify -ping -format "%m %w %h" /path/to/video.mp4[0]

[markevans]

it probably wouldn't hurt always analysing the first frame - feel free to send a pull request