Abstract: The present application discloses a method, system and medium of adding additional information to a LC3 audio code stream. The method comprises: obtaining unused bit space in a LC3 audio encoding process, including: obtaining an single-bit unused space of a current encoding frame in the LC3 audio encoding process, wherein the single-bit unused space is a difference value between an estimate length of a residual encoded bit and an actual length of the residual encoded bit of the current encoding frame in the LC3 audio encoding process; obtaining an multiple-bit unused space of the current encoding frame in the LC3 audio encoding process, wherein the multiple-bit unused space is an unused residual space of the current encoding frame in the LC3 audio encoding process; and adding additional information in the LC3 audio encoding process into the unused bit space, so as to be encoded.