The Helix MP3 Decoder

The Helix MP3 decoder provides MPEG-compliant decoding of MP3 content. Both floating-point and fixed-point decoder implementations are available. The fixed-point decoder is optimized especially for ARM processors but can run on any 32-bit fixed-point processor which can perform a long multiply operation (two 32-bit inputs generating a 64-bit result) and long multiply-accumulate (long multiply with 64-bit accumulator).

Key Features

• Pure 32-bit fixed-point implementation
• High-quality C reference code for porting to new platforms
• Optimized for ARM processors
• Fully reentrant and statically linkable
• Optional C++ API for compatibility with Helix clients
• Designed for high performance and low power consumption in handheld and mobile devices
• Full layer 3 support for
  • MPEG1 layer 3 - sampling frequencies: 48 KHz, 44.1 KHz, 32 KHz
  • MPEG2 layer 3 - sampling frequencies: 24 KHz, 22.05 KHz, 16 KHz
  • MPEG2.5 layer 3 - sampling frequencies: 12 KHz, 11.025 KHz, 8 KHz
• Supports constant bitrate, variable bitrate, and free bitrate modes
• Supports mono and all stereo modes (normal stereo, joint stereo, dual-mono)
• Option to use Intel® IPP performance libraries (if available)
  • Easy to link in either IPP libraries or Helix code

Technical Specifications

Average CPU Usage

Sample Rate	Channels	Bit Rate	Processor Model (1)
ARM7TDMI	ARM9TDMI-REV2	ARM920T	ARM9E	StrongARM1	XScale
48.0 KHz	2	320 Kbps	30 MHz	24 MHz	27 MHz	20 MHz	20 MHz	20 MHz
44.1 KHz	2	128 Kbps	26 MHz	21 MHz	24 MHz	17 MHz	17 MHz	17 MHz

(1) Tested with ARMulator, simulated zero-wait-state memory

Memory Usage

• ROM = 13446 Bytes (const globals)
• RAM = 23816 Bytes (heap)
  • Total Data Memory = 37262 Bytes
• Code Size = 21000 Bytes (approximately - depends on compiler)

Frequently Asked Questions

Where is the code in CVS?

• See the Helix Datatype project page: http://datatype.helixcommunity.org The CVS root is /cvsroot/datatype, and the module name (path) is mp3/codec/fixpt

Where does the build system put the code in my local source tree?

• datatype/mp3/codec/fixpt

How does the build system decide whether to build the fixed-point or floating-point MP3 decoder?

• If HELIX_CONFIG_FIXEDPOINT is defined in your profile, it will build the fixed-point decoder. Otherwise it will build the floating-point version.

整理自 https://www.helixcommunity.org/projects/datatype/Mp3dec

整理者 liuduanfei