Encoding and decoding media contents using code sequence to estimate audience

Systems and methods for estimating media audience are disclosed. In one aspect, a method includes receiving a media signal to be transmitted via a media distribution system, the media signal including multiple pieces of media content that each contain video and audio signals. One of the multiple pieces of media content within the received media signal are identified. It is determined that the identified piece of media content exceeds a threshold length, and, in response to determining that the identified piece of media content exceeds a threshold length, the audio signal of the identified piece of media content is encoded with a sequence of discrete codes. Each discrete code has a period that includes a set of sequential frequency components imperceptible to humans. The threshold length is greater than the period of a discrete code multiplied by the number of discrete codes in the sequence.