A method for processing an audio/video bit-stream includes the steps of receiving an input bit-stream, detecting whether the input bit-stream has a startcode emulation prevention pattern, and removing the startcode emulation prevention pattern from the input bit-stream to generate an output bit-stream and setting a flag signal as a first designated flag value when the startcode emulation prevention pattern is detected. The method further includes the step of detecting whether the input bit-stream includes a startcode, and directly outputting the input bit-stream and setting the flag signal as a second designated flag value when the startcode is detected.