An optical laser motion sensor like the Agilent ADNS 6000 is a very sophisticated possibility to touchlessly detect motion speed.
Since those sensors are built in many modern pc-mice, this part of high-tech is available at incredibly low prices.
The Keysonic Warp Laser Mouse is sold for 16 and includes everything you need, even the usb-serial communication driver.
The only thing I am not sure about, is the way of the data into the pc. As DGA access is a quite comfortable way, a self-
programmed device driver will have definetly less latency, and capturing of x and y motion information on a regular basis is
mandatory to guess the velocity right. See the software-section for more details on this later.

To make it short, laser mice are the first computer mice that suit our needs. Ball mice are too unprecise and normal optical
mice do not support the high resolution and picture rate, and though, high speeds (up to 0.4 m/s at 33 RPM and 100% speed) and
high resolutions can not be realised. Keysonic states to capture 6.700 fps at 1.600 dpi, making it possible to read input
speeds of up to 0.71 m/s which is enough to pitch a 12inch LP at 33 RPM to about 175% of its normal speed.

Thanks to integrated circuits, laser-mice are not the outstanding example for highly complex computer pheripheria any more.
Basically the have none less than those parts installed nowadays.

The hardware part is a laser diode that heavily illuminates the surface, the mouse is operated on. A 18x18 pixel camera captures
a picture of this surface 6.700 times a second and a microcomputer compares the pictures. Using fast fourier transformation,
it can now detect the motion that happened in the time between the to pictures.

Since the sensors have 1.600 dpi or more, it makes it possible to operate on almost any surface without significant loss of framerate.
Therefore we will be able to operate on a normal vinyl platter and no special "input"-platter is needed.
You might take a dive in the Agilent datasheets:
Agilent ADNS-6000 Lasermouse Sensor datasheet