In this paper, we propose a novel application of audio watermarking, estimation of recording location. The purpose of the paper is to determine the seat location in a theater at which a bootleg recording was made by using a digital video camera. In the proposed application, we embed different watermarks in the channels of the multi-channel sound of the movie. The multi-channel sound enters the air from multiple loudspeakers in a theater. If a monaural recording of the sound is made, the location of recording in the theater can be determined by detecting the multiple watermarks without any access to the host signals. The main idea is to use the time offsets of the watermark signals in the recorded signal. In simulation experiments, the recording locations can be determined within 1 m in almost all of the test cases. Although an experiment in a real environment resulted in more errors due to noise, these results successfully showed the potential applicability for practical use.