Synchronous infrasonic, video, and wave height measurements were performed during high surf at Polihale beach, Kauai, on March 4--12, 2005. During the experiment, atmospheric sound levels in the 0.5--20 Hz frequency band were associated with large breaking ocean waves. The envelope of surf infrasound signals yields breaking wave periods comparable to those derived from nearshore sea surface elevation measurements. Our analysis confirms that individual plunging waves are partly responsible for the generation of surf infrasound. We demonstrate the potential to extract breaking wave period from a single, well sited infrasonic microphone.