The present paper describes a method for indexing a piece of music using the TwinVQ (Transform-domain Weighted Interleave Vector Quantization) audio compression (MPEG-4 audio standard). First, we present a framework for indexing a piece of music based on the autocorrelation coefficients computed in the encoding step of TwinVQ audio compression. Second, we propose a new music feature that is robust with respect to bit rate based on the fact that the i-th autocorrelation coefficient with bit rate B₁ of a piece of music computed in the encoding step of TwinVQ audio compression can approximate the j-th autocorrelation coefficient with bit rate B₂ of the piece of music where i= left lfloor frac B_1 B_2 j right rfloor, and on the wavelet transform. Finally, we perform retrieval experiments on 1,023 pieces of polyphonic music with bit rate (8 kbps, 12 kbps, 16 kbps, 20 kbps, 24 kbps, 28 kbps, 32 kbps, 36 kbps, 40 kbps, and 44 kbps). The experimental results indicate that the proposed music feature for indexing has excellent retrieval performance for queries of various bit rates.