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 hit stream containing the compressed HOA representation corresponding to a plurality of hierarchical layers that include a base layer and one or more hierarchical enhancement layers, wherein the plurality of layers have assigned thereto components of a basic compressed sound representation of the sound or sound field, the components being assigned to respective layers in respective groups of components,
determining a highest usable layer among the plurality of layers for decoding;
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 obtainable on the basis 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, the transport signals assigned to the highest usable layer and any layers lower than the highest usable 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. 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 containing the compressed HOA representation corresponding to a plurality of hierarchical layers that include a base layer and one or more hierarchical enhancement layers, wherein the plurality of layers have assigned thereto components of a basic compressed sound representation of the sound or sound field, the components being assigned to respective layers in respective groups of components,
a decoder configured to:
determine a highest usable layer among the plurality of layers for decoding;
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 obtainable on the basis of 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, the transport signals assigned to the highest usable layer and any layers lower than the highest usable layer; and
parametrically enhance the decoded HOA representation using the side information included in the HOA extension payload assigned to the highest usable layer.
3. The method of claim 1 , wherein the layer information indicates a total number of additional ambient HOA coefficients for an enhancement layer.
4. The method of claim 1 , wherein the layer information includes HOA coefficient indices for each additional ambient HOA coefficient for an enhancement layer.
5. 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.
6. 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.
7. The method of claim 1 , wherein the layer information includes NumLayers elements, where each element indicates a number of transport signals included in all layers up to an i-th layer.
8. The method of claim 1 , wherein the layer information includes an indicator of all actually used layers for a k-th frame.
9. The method of claim 1 , wherein the layer information indicates that all of coefficients for predominant vectors are specified.
10. The method of claim 1 , wherein the layer information indicates that coefficients of the predominant vectors corresponding to a number greater than a MinNumOfCoeffsForAmbHOA are specified.
11. The method of claim 1 , wherein the layer information indicates MinNumOfCoeffsForAmbHOA and all elements defined in ContAddHoaCoeff are not transmitted, where lay is an index of layer containing vector based signal corresponding to a vector.