In this study, we propose a novel scheme for expanding chaotic keys for encrypting and decrypting image and video signals. The process begins with achieving chaos synchronization in semiconductor lasers driven using a common signal over a 130-km optical fiber link with a synchronization coefficient of 0.945. The resulting synchronized chaotic signal is processed through dual-threshold quantization, and error bits are removed through lower-triangle reconciliation, thereby yielding consistent keys at 1 Gbit/s. These keys are expanded to 80 Gbit/s using the Mersenne twister algorithm. Analysis shows that they can pass the NIST tests, thereby demonstrating good randomness and security. Thus, the encryption and decryption of image and video signals using these expanded keys is experimentally demonstrated.