Layered coding and data structure for compressed higher-order Ambisonics sound or sound field representations
The present document relates to a method of layered encoding of a frame of a compressed higher-order Ambisonics, HOA, representation of a sound or sound field. The compressed HOA representation comprises a plurality of transport signals. The method comprises assigning the plurality of transport signals to a plurality of hierarchical layers, the plurality of layers including a base layer and one or more hierarchical enhancement layers, generating, for each layer, a respective HOA extension payload including side information for parametrically enhancing a reconstructed HOA representation obtainable from the transport signals assigned to the respective layer and any layers lower than the respective layer, assigning the generated HOA extension payloads to their respective layers, and signaling the generated HOA extension payloads in an output bitstream. The present document further relates to a method of decoding a frame of a compressed HOA representation of a sound or sound field, an encoder and a decoder for layered coding of a compressed HOA representation, and a data structure representing a frame of a compressed HOA representation of a sound or sound field.
1. A method of decoding a compressed Higher Order Ambisonics (HOA) representation of a sound or sound field, the method comprising:
receiving a bit stream comprising the compressed HOA representation, wherein the bit stream comprises a plurality of hierarchical layers that comprise a base layer and one or more hierarchical enhancement layers,
determining a highest usable layer among the plurality of hierarchical layers for decoding;
determining that a parameter CodedVVecLength=2, and based on this determination determining that vector elements 1 to MinNumOfCoeffsForAmbHOA are not transmitted, and that coefficients of predominant vectors corresponding to a number greater than a MinNumOfCoeffsForAmbHOA are specified, wherein a VVecCoeffId array is determined based on MinNumOfCoeffsForAmbHOA;
extracting a HOA extension payload assigned to the highest usable layer, wherein the HOA extension payload includes side information for parametrically enhancing a reconstructed HOA representation corresponding to the highest usable layer, wherein the reconstructed HOA representation corresponding to the highest usable layer is based on of transport signals assigned to the highest usable layer and any layers lower than the highest usable layer;
decoding the compressed HOA representation corresponding to the highest usable layer based on layer information and the VVecCoeffId array, wherein the layer information indicates an active enhancement layer, and wherein the active enhancement layer can be used to determine a number of active directional signals in a current frame of the active enhancement layer; and
parametrically enhancing the decoded HOA representation using the side information included in the HOA extension payload assigned to the highest usable layer.
2. The method of claim 1 , wherein the layer information includes enhancement information that includes at least one of Spatial Signal Prediction, Sub-band Directional Signal Synthesis and Parametric Ambience Replication Decoder.
3. The method of claim 1 , further including v-vector elements that are not transmitted for indices that are equal to indices of additional HOA coefficients included in a set of ContAddHoaCoeff.
4. The method of claim 1 , wherein the layer information includes NumLayers elements, where each element indicates a number of the transport signals included in all layers up to an i-th layer.
5. The method of claim 1 , wherein the layer information includes an indicator of all actually used layers for a k-th frame.
6. A non-transitory carrier medium carrying computer executable code that, when executed on a processor, causes the processor to perform a method according to claim 1 .
7. An apparatus for decoding a compressed Higher Order Ambisonics (HOA) representation of a sound or sound field, the apparatus comprising:
a receiver configured to receive a bit stream comprising the compressed HOA representation, wherein the bit stream comprises a plurality of hierarchical layers that comprise a base layer and one or more hierarchical enhancement layers,
a decoder configured to:
determine a highest usable layer among the plurality of hierarchical layers for decoding;
determine that a parameter CodedVVecLength=2, and based on this determination determining that vector elements 1 to MinNumOfCoeffsForAmbHOA are not transmitted, and that coefficients of predominant vectors corresponding to a number greater than a MinNumOfCoeffsForAmbHOA are specified, wherein a VVecCoeffId array is determined based on MinNumOfCoeffsForAmbHOA;
extract a HOA extension payload assigned to the highest usable layer, wherein the HOA extension payload includes side information for parametrically enhancing a reconstructed HOA representation corresponding to the highest usable layer, wherein the reconstructed HOA representation corresponding to the highest usable layer is based on transport signals assigned to the highest usable layer and any layers lower than the highest usable layer;
decode the compressed HOA representation corresponding to the highest usable layer based on layer information and the VVecCoeffId array, wherein the layer information indicates an active enhancement layer, and wherein the active enhancement layer can be used to determine a number of active directional signals in a current frame of the active enhancement layer; and
parametrically enhance the decoded HOA representation using the side information included in the HOA extension payload assigned to the highest usable layer.