IEC 61937-11:2010 pdf – Digital audio-Interface for non-linear PCM encoded audio bitstreams applyingIEC60958- Part 11: MPEG-4 AAC and its extensions in LATM/LOAS
IEC 61937-11:2010 pdf – Digital audio-Interface for non-linear PCM encoded audio bitstreams applyingIEC60958- Part 11: MPEG-4 AAC and its extensions in LATM/LOAS.
HE AAC bit streams with downsampled SBR shall be transmitted signaling AAC LC in the subdata-type, Therefore one access unit corresponds to 1 024 or 960 AAC encoded audio sam pies.
If HE AAC is signaled by the sub-data-type the IEC 60958 frame rate shall be equal to the sampling frequency of the SBR tool. If AAC LC is signaled the IEC 60958 frame rate shall correspond to the sampling frequency of AAC.
The reference point of a data-burst is bit 0 of Pa and occurs exactly once every number of
IEC 60958 sampling periods which is computed using the information from Table I and
Table 3. The data-burst containing one LATULOAS audio frame shall occur at a constant rate.
The intervals for data-bursts sharing the same bit-stream-number shall correspond exactly to
the amount of IEC 60958 frames which is calculated using the information from Table I and
It Is not allowed to transmit audio data sireams using IEC 60958 frame rates below 32 kHz.
5.3.2 LATM/LOAS framing
The LOAS frame as described in ISO/IEC 14496-3 shall be mapped directly to the payload section. right after the preamble words of the data-burst. The first bit of the LOAS frame shall always correspond to the first bit after the preamble section in the data-burst.
The payload in a data-burst consists of one complete LOAS frame containing one LATM AudioMuxElement. It is not allowed to convey one LATM!LOAS frame using multiple databursts. LOAS frames exceeding the payload capacity of a data-burst shall be dropped and the actual data-burst shall be replaced by a sequence of pause-bursts to match the duration 01 that data-burst.
The parameter nuniSubFrames from the LATM StreamMuxConhig shall be 0. The parameter numProgram from the LATM StreamMuxConfig shall be 0. The parameter numlayer from the LATM StreamMuxConfig shall be 0 except for audio streams signaling the availability of UPS with payload embedding and explicit signaling of UPS in the second LATM layer. In such cases the presence of a second layer in LATM Irames is allowed and therefote numLayer shall be 1 indicating 2 layers. In this conliguration there exists no payload associated to the second LATM layer and therefore the payload size indication for the second layer in LATM is set to zero.
Only the LOAS AudloSyncStream() scheme shall be used in the context of this specification.
The LATM StreamMuxConfig structure shall be conveyed inside the LATU multiplex. This is the main structure that is utilized by the decoder for configuration. The StreamMuxConfig may not be present in each LATM frame in order to save bandwidth. It may be sent in intervals to allow decoders to tune In to a running stream.
The latency of an external audio decoder to decode MPEG-4 AAC and its extensions in LATMILOAS Is defined as the sum of the receiving lime of I he audio payload in one data-burst and the time used for decoding 01 one access unit.
Each data-burst contains a minimum of 4 stuffing words (Pz of 16 bIts). The repetition period of data-bursts in lEG 60958 frames is computed according to information from Table 1 and Table 3. The reception delay for one audio access unit Is calculated as the time elapsed counting from the first bit of the data-burst until the last bit of the actual audio payload Inside the data-burst received. Subsequent stuffing Is not taken into account. After a complete frame Is received immediate decoding and subsequent rendering of the audio frame is not recommended as the size of the next audio frame and therefore time required for receiving It completely cannot be determined accurately.