This paper describes a high-speed optical camera communication (OCC) technique using an LED and a rolling-shutter camera. In the proposed technique, the symbols being transmitted are encoded as time delays of optimally modulated signals derived theoretically. A receiver decodes the symbols by using intensities obtained from four consecutive line sensors of a camera. Experiments using a camera having performance similar to that of a general-purpose camera show that the proposed technique can achieve 0.833 - 1.17 bits per line sensing and that symbol transmission is possible with a longer exposure time setting; this is difficult to achieve using existing on--off keying OCC techniques.