IEC 61937-4:2003

Overview

IEC 61937-4:2003 defines how non-linear PCM bitstreams in the MPEG audio format are carried over the digital audio interface specified in IEC 60958 (commonly implemented as S/PDIF or AES3). It is part of the IEC 61937 family that standardizes the encapsulation of compressed audio (AC‑3, DTS, MPEG, AAC, etc.) into IEC 60958 frames so that external decoders can detect, extract and correctly decode streamed bitstreams.

Key topics and technical requirements

• Mapping and burst format: Specifies the mapping of MPEG audio frames onto IEC 61937 data‑bursts with a preamble and burst‑payload.
• Burst‑info field: A 16‑bit burst‑info word identifies the data‑type (bits 0–4) and repetition period; data‑type values include:
  • 04h - MPEG‑1 Layer‑1 (384 samples/channel)
  • 05h - MPEG‑1 Layer‑2 or Layer‑3, or MPEG‑2 without extension (1 152 samples/channel)
  • 06h - MPEG‑2 with extension (1 152 samples/channel)
• Pause data‑bursts and gap filling: Defines use and recommended repetition periods for pause bursts to fill stream gaps (typically 32 or 64 IEC 60958 frames depending on the MPEG data‑type) and a gap‑length parameter to indicate missing decoded PCM samples.
• Latency and synchronization: Provides rules for calculating decoder latency (time to receive full burst plus decoding delay) so transmitters can schedule bursts to maintain A/V sync. Example latencies (for MPEG‑1 Layer‑2/3 or MPEG‑2 without extension) are specified: 20.9 ms at 48 kHz, 22.75 ms at 44.1 kHz, and 31.35 ms at 32 kHz.
• Data‑type specific fields and stuffing: Describes how stream stuffing is applied, the structure of base and extension frames (e.g., MPEG‑2 extension frames for multi‑channel), and minimal fields needed in the burst info.

Applications and who uses it

• Consumer electronics manufacturers - implement S/PDIF/AES3 outputs on DVD/Blu‑ray players, set‑top boxes, game consoles and AV receivers to transport MPEG compressed audio reliably to external decoders.
• Audio/video system integrators - ensure correct A/V synchronization and interoperability across devices.
• Firmware/driver and DSP developers - encode/decode and schedule MPEG audio bursts, implement pause burst handling and latency compensation.
• Test labs and compliance engineers - verify adherence to IEC 61937‑4 framing, burst‑info correctness, repetition periods and latency behavior.

Related standards

• IEC 60958 - Digital audio interface (S/PDIF/AES3) - mandatory normative reference.
• IEC 61937‑1 - General rules and burst mapping conventions for non‑linear PCM bitstreams.
• Other IEC 61937 parts cover AC‑3, DTS, AAC and ATRAC formats.

Keywords: IEC 61937-4, IEC 60958, digital audio interface, MPEG audio, non-linear PCM bitstreams, data-burst, burst-info, latency, pause data-burst, S/PDIF, AES3.