A device (24; 1002A) configured to process a backward compatible bitstream, the device comprising: one or more memories configured to store at least a portion of the backward compatible bitstream, wherein the backward compatible bitstream conforms to a legacy transport format, the legacy transport format comprises an audio data transport stream, ADTS, frame for legacy audio data and one or more associated fill elements (350A - 350E), and the legacy audio data comprises mono audio data or stereo audio data; and one or more processors configured to: obtain, from the ADTS frame of the backward compatible bitstream, legacy audio data; obtain, from one or more fill elements (350A - 350E) of the backward compatible bitstream associated with the ADTS frame, a header including one or more indications indicative of how extended audio data, that enhances the legacy audio data, was specified in the backward compatible bitstream; obtain, from the one or more fill elements (350A - 350E) of the backward compatible bitstream and based on the one or more indications, the extended audio data; obtain, from the legacy audio data, first higher order ambisonic audio data, wherein the extended audio data comprises second higher order ambisonic audio data, and the second higher order ambisonic audio data comprises one or more higher order ambisonic coefficients corresponding to spherical basis functions having an order greater than zero or one; and render, based on the first higher order ambisonic audio data and the second higher order ambisonic audio data, output speaker feeds with increased soundfield resolution as compared to the legacy audio format. one or more memories configured to store at least a portion of the backward compatible bitstream, wherein the backward compatible bitstream conforms to a legacy transport format, the legacy transport format comprises an audio data transport stream, ADTS, frame for legacy audio data and one or more associated fill elements (350A - 350E), and the legacy audio data comprises mono audio data or stereo audio data; and one or more processors configured to: obtain, from the ADTS frame of the backward compatible bitstream, legacy audio data; obtain, from one or more fill elements (350A - 350E) of the backward compatible bitstream associated with the ADTS frame, a header including one or more indications indicative of how extended audio data, that enhances the legacy audio data, was specified in the backward compatible bitstream; obtain, from the one or more fill elements (350A - 350E) of the backward compatible bitstream and based on the one or more indications, the extended audio data; obtain, from the legacy audio data, first higher order ambisonic audio data, wherein the extended audio data comprises second higher order ambisonic audio data, and the second higher order ambisonic audio data comprises one or more higher order ambisonic coefficients corresponding to spherical basis functions having an order greater than zero or one; and render, based on the first higher order ambisonic audio data and the second higher order ambisonic audio data, output speaker feeds with increased soundfield resolution as compared to the legacy audio format. obtain, from the ADTS frame of the backward compatible bitstream, legacy audio data; obtain, from one or more fill elements (350A - 350E) of the backward compatible bitstream associated with the ADTS frame, a header including one or more indications indicative of how extended audio data, that enhances the legacy audio data, was specified in the backward compatible bitstream; obtain, from the one or more fill elements (350A - 350E) of the backward compatible bitstream and based on the one or more indications, the extended audio data; obtain, from the legacy audio data, first higher order ambisonic audio data, wherein the extended audio data comprises second higher order ambisonic audio data, and the second higher order ambisonic audio data comprises one or more higher order ambisonic coefficients corresponding to spherical basis functions having an order greater than zero or one; and render, based on the first higher order ambisonic audio data and the second higher order ambisonic audio data, output speaker feeds with increased soundfield resolution as compared to the legacy audio format.