Rendering of multichannel audio using interpolated matrices

A method for recovery of M channels of an N-channel audio program, wherein the program is specified over a time interval, the time interval includes a subinterval from a time t1 to a time t2, and a time-varying mix, A(t), of N encoded signal channels to M output channels has been specified over the time interval, said method including steps of:

• obtaining an encoded bitstream which is indicative of encoded audio content, interpolation values, and a first cascade of N×N primitive matrices, wherein an N×N primitive matrix is defined as a matrix in which N−1 rows contain off-diagonal elements equal to zero and on-diagonal elements with an absolute value of 1;
• and
• performing interpolation to determine a sequence of cascades of N×N updated primitive matrices, from the interpolation values, the first cascade of primitive matrices, and an interpolation function over the subinterval, wherein
• the first cascade of N×N primitive matrices, when applied to samples of N encoded signal channels of the encoded audio content, implements a first mix of audio content of the N encoded signal channels to the M output channels, wherein the first mix is consistent with the time-varying mix, A(t), in the sense that the first mix is at least substantially equal to A(t1), and
• the interpolation values, with the first cascade of primitive matrices, and the interpolation function, are indicative of a sequence of cascades of N×N updated primitive matrices, such that each of the cascades of updated primitive matrices, when applied to samples of the N encoded signal channels of the encoded audio content, implements an updated mix, associated with a different time in the subinterval, of the N encoded signal channels to the M output channels, wherein each said updated mix is consistent with the time-varying mix, A(t).