This standard is part of a suite documenting carriage constraints of Next Generation Audio (NGA) codecs in MPEG-2 transport systems and in MPEG DASH. It is intended to be used in conjunction with the specific audio technologies described in subsequent Parts of this standard (see [SCTE 243-1]).
This document is part of a three-part standard that specifies carriage constraints of Next Generation Audio (NGA) codecs in MPEG-2 transport systems and in MPEG DASH. In conjunction with [SCTE 243-1] this document defines the carriage of AC-4 audio in MPEG-2 transport systems and MPEG DASH.
The Next Generation Audio (NGA) system audio system provides immersive and personalizable sound for television. AC-4 supports the generation of coded audio frames that represent the same time interval as the associated video frame. With this frame alignment, audio can be passed transparently through a cable, satellite, or Internet Protocol Television (IPTV) turnaround facility, eliminating the need to decode and re-encode audio to correct time-base differences or to perform switching/splicing. All common integer and fractional video frame rates are supported.
To select the correct frame rate and time-align the audio frame boundaries to video, the AC-4 encoder is provided with reference timing information. There is a direct whole-frame relationship between video and audio frames from a reference time, such as at the start of a coded video sequence or at a random access point (RAP).
Note that NGA is not compatible with the audio system used in [SCTE 54-era service.