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

# Appendix G: COR1 Corrigenda Changes to MP4-SA

## User-Defined Opcodes

New normative rate semantics describe the execution of i-rate statements in kopcodes and k-rate and i-rate statements in aopcodes. New restrictions limit the use of k-rate and a-rate variables and statements in user-defined polymorphic opcodes.

## Opcode Call Rate Semantics

New normative rate semantics describe the execution of kopcode calls in a-rate statements and iopcode calls in k-rate or a-rate statements. Explained in both core opcode and user-defined opcode chapters.

## If and If-Else Rate Semantics

New normative rate semantics describe the execution of i-rate statements in k-rate if and if-else statement blocks, and i-rate and k-rate statements in a-rate if and if-else statement blocks.

## Standard Names

SAOL programs may alter the value of writable standard names (MIDIctrl and params) by using the call by reference semantics of user-defined opcodes.

## Core Opcodes

The syntax and semantics of the compressor core opcode has changed: all programs using this opcode will need to be altered. Significant semantic changes have also been made to the spectral opcodes. Minor clarifications have been made to several other core opcodes; consult COR 1 for details.

## Wavetable Generators

The semantics of the concat and the window wavetable generator have been clarified.

## MIDI

MP4-SA encodings that use the midi_file chunk now use the default tempo of the MIDI File standard (120 beats/minute). New normative semantics for monitoring MIDI standard names in dynamic, effects, and SASL instruments. Correct semantics for the All Sounds Off and All Notes Off MIDI commands.

## Miscellaneous

New semantics for user-defined opcodes without return statements, and for empty return statements. New semantics of event triggering in the decoder execution cycle: an event occurs if its timestamp is less than or equal to the current score time. Corrections to the SAOL operator precedence table.

Appendix H:

Aspects of MP4-SA Not Covered in This Book

Copyright 1999 John Lazzaro and John Wawrzynek.