Initial public release of the 2024A software.
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Joe Kearney
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Fixed-point MP3 decoder
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Developed by RealNetworks, 2003
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===============================
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Overview
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--------
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This module contains a high-performance MPEG layer 3 audio decoder for 32-bit fixed-point
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processors. The following is a quick summary of what is and is not supported:
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Supported
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- layer 3
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- MPEG1, MPEG2, and MPEG2.5 (low sampling frequency extensions)
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- constant bitrate, variable bitrate, and free bitrate modes
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- mono and all stereo modes (normal stereo, joint stereo, dual-mono)
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Not currently supported
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- layers 1 and 2
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Highlights
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----------
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- highly optimized for ARM processors (details in docs/ subdirectory)
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- reference x86 implementation
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- C and assembly code only (C++ not required)
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- reentrant, statically linkable
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- low memory (details in docs/ subdirectory)
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- option to use Intel Integrated Performance Primitives (details below)
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Supported platforms and toolchains
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----------------------------------
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This codec should run on any 32-bit fixed-point processor which can perform a full 32x32-bit
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multiply (providing a 64-bit result). The following processors and toolchains are supported:
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- x86, Microsoft Visual C++
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- ARM, ARM Developer Suite (ADS)
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- ARM, Microsoft Embedded Visual C++
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- ARM, GNU toolchain (gcc)
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- RISC-V, GNU toolchain (gcc)
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ARM refers to any processor supporting ARM architecture v.4 or above. Thumb is not required.
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Typically this means an ARM7TDMI or better (including ARM9, StrongARM, XScale, etc.)
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Generally ADS produces the fastest code. EVC 3.0 does not support inline assembly code for
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ARM targets, so calls to MULSHIFT32 (smull on ARM) are left as function calls. For the
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fastest code on targets which do not normally use ADS consider compiling with ADS,
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using the -S option to output assembly code, and feeding this assembly code to the assembler
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of your choice. This might require some syntax changes in the .S file.
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Adding support for a new processor is fairly simple. Simply add a new block to the file
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real/assembly.h which implements the required inline assembly functions for your processor.
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Something like
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...
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#elif defined NEW_PROCESSOR
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/* you implement MULSHIFT32() and so forth */
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#else
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#error Unsupported platform in assembly.h
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#endif
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Optionally you can rewrite or add assembly language files optimized for your platform. Note
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that many of the algorithms are designed for an ARM-type processor, so performance of the
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unmodified C code might be noticeably worse on other architectures.
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Adding support for a new toolchain should be straightforward. Use the sample projects or the
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Umakefil as a template for which source files to include.
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Directory structure
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-------------------
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fixpt/ platform-independent code and tables, public API
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fixpt/docs algorithm notes, memory and CPU usage figures, optimization suggestions
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fixpt/ipp source code which uses IPP for decoding (see the "IPP" section below)
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fixpt/pub public header files
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fixpt/real source code for RealNetworks' MP3 decoder
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fixpt/testwrap sample code to build a command-line test application
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Code organization
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-----------------
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fixpt/
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mpadecobj.cpp optional shim which exports API used by Helix clients (see mp3/renderer)
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mp3dec.c main decode functions, exports C-only API
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mp3tabs.c common tables used by all implementations (bitrates, frame sizes, etc.)
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fixpt/pub/
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mp3common.h defines low-level codec API which mp3dec.c calls
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mp3dec.h defines high-level codec API which applications call
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mpadecobjfixpt.h optional C++ shim API (only necessary if mpadecobj.cpp is used)
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statname.h symbols which get name-mangled by C preprocessor to allow static linking
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fixpt/ipp source code for wrapper files which link in IPP libraries
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fixpt/real full source code for RealNetworks MP3 decoder
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To build an MP3 decoder library, you'll need to compile the top-level files and EITHER
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real/*.c OR ipp/*.c and the correct IPP library.
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Decoder using Real code: mp3dec.c + mp3tabs.c + real/*.c + real/arm/[files].s (if ARM)
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Decoder using IPP code: mp3dec.c + mp3tabs.c + ipp/*.c + ippac*.lib
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Although the real/ and ipp/ source code follow the same top-level API (for Dequantize(),
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Subband(), etc.) mixing and matching is not guaranteed to work. The outputs might
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be ordered differently for optimization purposes, scaled differently, etc.
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IPP
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---
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For certain platforms Intel® has created highly-optimized object code libraries of DSP
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routines. These are called the Intel® Integrated Performance Primitives (IPP). If IPP
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libraries are available for a platform, this MP3 decoder can link them in and use them
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instead of the RealNetworks source code. To use IPP, you still need to build the top-level
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files (mp3dec.c, mp3tabs.c). You also build the files in ipp/*.c. These are just thin
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wrappers which provide the glue logic between the top-level decode functions in
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mp3dec.c and the optimized DSP primitives in the IPP libraries. IPP libraries are not
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included in this module. You must obtain them WITH A LICENSE directly from Intel.
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Further info on the latest versions of IPP (as of the date of this readme) is available
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from the URLs below
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Intel® Integrated Performance Primitives for the
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Intel® PXA25x and PXA26x family of Processors, Version 3.0
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* http://www.intel.com/design/pca/applicationsprocessors/swsup/IPPv30.htm
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Intel® Integrated Performance Primitives for
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Intel® Pentium® Processors and Intel® Itanium® Architectures
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* http://www.intel.com/software/products/ipp/ipp30/
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These sites explain how to obtain IPP and the terms under which IPP libraries may be used.
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The code in this module is merely wrapper code which calls IPP functions. You are fully
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responsible for adhering to the license agreement under which you obtain the IPP
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libraries from Intel.
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To-Do list and status
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---------------------
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faster/lower-memory dequantizer (in progress)
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tighter fixed-point scaling (in progress)
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remove all run-time math calls (/, %) (in progress)
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ARM assembly code for DCT32, IMDCT (if necessary)
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add test scripts and compliance docs
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write 32-bit C polyphase filter
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(where 64-bit MACC not available)
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As these optimizations are completed, they will be added to the Helix codebase. Please
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continue to check there for updates. Changes will be noted in this readme.
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readme.txt last updated 07/23/03
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