### From The MPEG-4 Structured Audio Book by John Lazzaro and John Wawrzynek.

# Appendix H: Aspects of MP4-SA Not Covered in This Book

## Introduction

Several part of MPEG 4 Structured Audio are not discussed in the book. In this Appendix, we briefly describe these topics, and provide a pointer to the part(s) of the standards document (FDIS ISO/IEC 14496-3:1999(E), edited by Eric Scheirer) that explains the topic.

The uncovered topics are listed on the right panel. Several of these topics concern language features not included in `sfront`, such as AudioFX support and SASBF synthesis.

The other topics on the right panel are standards-oriented issues, such as the binary layout of an MP4 file, that is not usually necessary knowledge for SAOL programmers.

## Uncovered Topics and FDIS Page Numbers

#### Language Features

- `sasbf` (p. 52, 107) An atomic element in expressions, that implements a sample-bank based synthesizer algorithm. Its primary purpose in life is to support Object 2 MP4-SA decoders, which don't use SAOL and SASL. Not in `sfront`.
- AudioFX elements (p. 56, 114). SAOL can be used in other parts of MP4 as a support language for effects processing. The standard names position, direction, listenerPosition, listenerDirection, minFront, maxFront, minBack, maxBack, and params support this application. Control drivers in `sfront` are able to support these variables, but none do at present.
- `fx_speedc` core opcode (p. 95) A core opcode for changing the sampling rate of an input_bus. Not supported in `sfront`.

#### Standards Issues

- Binary MP4-SA Files (p. 16, 106, 116). How to read and write the MP4 binary encoding.
- Decoding Process (p. 21). Exact normative description of how a SAOL program starts up, and how an orchestra cycle executes.
- Random Access (p. 131). How to write SAOL and SASL so that the audio can be "fast-forwarded and reversed" easily.

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Copyright 1999 John Lazzaro and John Wawrzynek.