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

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


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.

Return to: Appendix Cover Page

Copyright 1999 John Lazzaro and John Wawrzynek.