Audio Wave

关于Wave格式

Study Of Wave Formate

Posted by 李AA on February 23, 2020

前言

  • Wave文件应该是音频领域使用最广泛的容器格式了.对于Wave文件的解析器(Parser),也是构建音频引擎的重要组件.本文受数字音频规范与程序设计与Waveless项目启发,意在搭建一个简单parser模型来更好的理解Wave文件格式.

一些Wave格式标准

  • Wave格式是属于RIFF(Resourse Interchange File Format)规范的格式之一.这个规范下的多媒体格式还有.RMI/.RMN/.ANI

  • Wave文件支持所有ACM规范下的编码格式,常用的有PCM/ADPCM.

  • Wave文件常用采样率为11.025kHz/44.1kHz/48kHz/96kHz.常用采样精度为8bit/16bit/24bit/32bit

  • 8bit采样精度使用unsigned char来表示,取值范围0~255.16bit采样精度使用signed short来表示,取值范围-32768 ~ 32767.24bit/32bit通常采用浮点类型来表示,也可以使用signed int来表示,取值范围−8388608 ~ 8388607.

  • PCM编码(非ADPCM压缩编码)的wav文件大小 = 采样率(sample rate) * 采样精度(bit depth) * 声道数 * 时长/8

文件结构

  • wave文件由基础Chunk和SubChunk组成，下图是基础Chunk。包含了基本文件信息和采样点数据。

  • 根据8~12字节的format信息可以将文件类型分为三种

  1. PCM Formate (WAVE_FORMAT_PCM)
    • 标准的PCM文件类型
  2. Non-PCM Formats (WAVE_FORMAT_IEEE_FLOAT / WAVE_FORMAT_ALAW / WAVE_FORMAT_MULAW)
    • 浮点编码或者压缩编码的PCM类型
  3. Extensible Format (WAVE_FORMAT_EXTENSIBLE)
    • fmt chunk中有其他sub-chunk时的类型

Chunk数据

  • Wave格式的元数据是通过各类Chunk数据块组合而成,不同类型Chunk块储存不同的种类元数据,Chunk也是元数据组合的最小单位.

    • RIFF Chunk

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      struct RIFFChunk
{
  //RIFF规范标识符 : "RIFF"
  char ckID[4];
  //RIFF Chunk 大小
  unsigned long ckSize;
  //Wave格式ID: "WAVE"
  char WavID[4];
};

    • Standard Format Chunk

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    struct StandardPCMFmtChunk
{
  //Chunk ID: "fmt"
  char ckID[4];
  //fmt Chunk 大小
  unsigned long ckSize;
  //音频数据的编码格式
  unsigned short wFormatTag;
  //声道数
  unsigned short nChannels;
  //采样率
  unsigned long nSamplesPerSec;
  //每秒码率
  unsigned long nAvgBytesPerSec;
  //对齐占位数据 2=16-bit mono, 4=16-bit stereo
  unsigned short nBlockAlign;
  //采样精度
  unsigned short wBitsPerSample;
};

    • Non-PCM Format Chunk

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      struct NonPcmFmtChunk
{
//与Standard Format Chunk相同
StandardPCMFmtChunk standardFmtChunk;
  //extension Chunk的大小
  unsigned short cbSize;
};

    • Extensible Format Chunk

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      struct ExtensibleFmtChunk
{
//与Standard Format Chunk相同
  StandardPCMFmtChunk standardFmtChunk;
  //extension Chunk的大小
  unsigned short cbSize;
  //实际有效的编码位,比如12bit的编码方式采样精度显示的是16bit,实际有效编码位只有12bit
  unsigned short wValidBitsPerSample;
  //回放音响的布局
  unsigned long dwChannelMask;
  //GUID标识符(头两位是subformat信息,剩余12位是GUID标识符)
  char SubFormat[16];
};

    • Data Chunk

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      struct DataChunk
{
  //Chunk ID: "data"
  char ckID[4];
  //实际音频数据大小
  unsigned long ckSize;
};

    • Fact Chunk

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      struct FactChunk
{
  //Chunk ID: "fact"
  char ckID[4];
  //fact Chunk 大小
  unsigned long ckSize;
  //每个声道采样数
  unsigned long dwSampleLength;
};

    • Bext Chunk

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      struct BextChunk
{
  //Chunk ID = "bext"
  char ckID[4];
//bext chunk 大小
  unsigned long ckSize;
//文件描述信息
  char Description[256];
//创作者信息
  char Originator[32];
//创作者关联信息
  char OriginatorReference[32];
//创作日期
  char OriginationDate[10];
//创作时间 <<hh::mm::ss>>
  char OriginationTime[8];
  //对齐占位数据
  unsigned short Align = 0;
//参考时间 低位
  unsigned long TimeReferenceLow;
//参考时间 高位
  unsigned long TimeReferenceHigh;
//BWF版本号
  unsigned short Version;
//SMPTE UMID数据
  char UMID[64];
//集成响度值 LUFS
  short LoudnessValue;
//响度范围值 LU
  short LoudnessRange;
//TruePeak峰值 dBTP
  short MaxTruePeakLevel;
//瞬时响度均值 LUFS
  short MaxMomentaryLoudness;
//ShortTerm响度均值 LUFS
  short MaxShortTermLoudness;
//预留空间 现在全为0
  char Reserved[180];
};

    • Junk Chunk

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      struct JunkChunk
{
  //Chunk ID = "JUNK"
  char ckID[4];
//Junk Chunk 大小
  unsigned long ckSize;
//无效数据
  char initialData[74];
};

    • RF64 Chunk

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      struct RF64Chunk
{
  // Chunk ID = "RF64"
  char ckID[4]; 
  // -1 不要使用这个数据,用DS64 Chunk里面的riffSizeHigh 和 riffSizeLow来获取大小
  unsigned long ckSize;
  // Type ID = "WAVE"
  char rf64Type[4]; 
};

    • DS64 Chunk

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      struct DS64Chunk
{
  // Chunk ID = "DS64"
  char ckID[4];
//DS64 Chunk大小
  unsigned long ckSize;
//RF64 Chunk大小的低四位
  unsigned long RIFFSizeLow;
//RF64 Chunk大小的高四位
  unsigned long RIFFSizeHigh;
//Data Chunk数据大小的低四位
  unsigned long DataSizeLow;
//Data Chunk数据大小的高四位
  unsigned long DataSizeHigh;
//fact Chunk采样数大小低四位
  unsigned long SampleCountLow;
//fact Chunk采样数大小高四位
  unsigned long SampleCountHigh;
//Table数组的大小
  unsigned long TableLength;
};

    • PAD Chunk

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      struct PadChunk
{
//Chunk ID = "PAD"
  char ckID[4];
//Pad Chunk大小
  unsigned long ckSize;
};

    • 一些不常用扩展Chunk

      1. Cue Chunk
      2. Playlist Chunk
      3. Associated Data Chunk
      4. Instrument Chunk
      5. Sample Chunk

Header分类

  • Standard PCM

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  struct StandardWavHead
  {
  	RIFFChunk RIFFChunk;
  	StandardPCMFmtChunk fmtChunk;
  	DataChunk DataChunk;
  };

  • Non-PCM

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  //基本少有单独是Non-PCM类型的Header,因为Non-PCM Header只是包含了Extensible  Header的基础数据类型
  struct NonPcmHead
  {
  	RIFFChunk RIFFChunk;
  	NonPcmFmtChunk fmtChunk;
  	FactChunk FactChunk;
  	DataChunk DataChunk;
  };

  • Extensible

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  struct ExtensibleWavHead
  {
  	RIFFChunk RIFFChunk;
  	ExtensibleFmtChunk fmtChunk;
  	FactChunk FactChunk;
  	DataChunk DataChunk;
  };

  struct ExtensibleNoFactHead
  {
  	RIFFChunk RIFFChunk;
  	ExtensibleFmtChunk fmtChunk;
  	DataChunk DataChunk;
  };

  • BWF

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  //EBU制定的Wave格式扩展标准,增加了大量的元数据供使用
  struct StandardBWFHead
  {
  	RIFFChunk RIFFChunk;
  	StandardPCMFmtChunk fmtChunk;
  	BextChunk BextChunk;
  	JunkChunk JunkChunk;
  	DataChunk DataChunk;
  };

  struct RF64Header
  {
  	RF64Chunk RF64Chunk;
  	DS64Chunk DS64Chunk;
  	//std::vector<CS64Chunk> TableChunk;
  	ExtensibleFmtChunk fmtChunk;
  	BextChunk BextChunk;
  	//JunkChunk JunkChunk;
  	DataChunk DataChunk;
  };

  struct ExtensibleBWFHead
  {
  	RIFFChunk RIFFChunk;
  	ExtensibleFmtChunk fmtChunk;
  	FactChunk FactChunk;
  	BextChunk BextChunk;
  	JunkChunk JunkChunk;
  	DataChunk DataChunk;
  };

Data数据类型

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  enum class WavDataType
  {
  	Invalid,
  	//usigned int8
  	WavData8bit,
  	//int12
  	WavData12bit,
  	//int16
  	WavData16bit,
  	//int24
  	WavData24bit,
  	//float32
  	WavData32bit,
  	//float64
  	WavData64bit
  };

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  signed-integer
  PCM data stored as signed (‘two’s complement’) integers. Commonly used with a 1or 24 −bit encoding size. A value of 0 represents minimum signal power.
  
  unsigned-integer
  PCM data stored as unsigned integers. Commonly used with an 8-bit encoding size. value of 0 represents maximum signal power.
  
  floating-point
  PCM data stored as IEEE 753 single precision (32-bit) or double precision (64-bitfloating-point (‘real’) numbers. A value of 0 represents minimum signal power.
  
  a-law 
  International telephony standard for logarithmic encoding to 8 bits per sample. Ihas a precision equivalent to roughly 13-bit PCM and is sometimes encoded witreversed bitordering (see the −X option).
  
  u-law, mu-law
  North American telephony standard for logarithmic encoding to 8 bits per sampleA.k.a.µ-law. It has a precision equivalent to roughly 14-bit PCM and is sometimeencoded with reversed bit-ordering (see the −X option).
  
  oki-adpcm
  OKI (a.k.a. VOX, Dialogic, or Intel) 4-bit ADPCM; it has a precision equivalent to
  roughly 12-bit PCM. ADPCM is a form of audio compression that has a goocompromise between audio quality and encoding/decoding speed.

  ima-adpcm
  IMA (a.k.a. DVI) 4-bit ADPCM; it has a precision equivalent to roughly 13-bit PCM.
  
  ms-adpcm
  Microsoft 4-bit ADPCM; it has a precision equivalent to roughly 14-bit PCM.
  
  gsm-full-rate
  GSM is currently used for the vast majority of the world’s digital wirelestelephone calls.It utilises several audio formats with different bit-rates anassociated speech quality.

  • Data数据的一些标准

    • I/O

      Wave采样数据点的取值范围和采样精度相关联.CPU对于数据帧的IO操作是以8位为基础单位的,所以数模转换器产生(ADC)产生的数据也是8的整数倍.

    • 左对齐(left-justified)

      采样点数据使用左对齐,剩余的比特位在右边用零填充.比如12bit数据101011101011补全为1010111010110000.

    • 小端编码(little endian)

      低比特位在低地址位.内存内布局: 10110000|10101110.

    • 采样帧(sample frame)

      • 同时播放的采样点称作采样帧。多声道文件的采样点数据是交替储存的。
      • stereo [left right]
      • 3.0 [left right center]
      • quad [front left front right rear left rear right]
      • 4.0 [left center right surround]
      • 5.1 [left center left center right center right surround]

WaveParser

GitHub

  • Parser设计思路

    我准备了22个各种Header类型的测试文件,以正确解析所有文件为标准,只负责Header数据的解析,暂时没有Header信息的编辑以及Data部分的处理.

  • Parser的使用

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    #include "WavParser.h"
#include "WavUtility.h"

int main()
{
  const std::string& FilePath = "MyFileFolder/MyFile.wav"

  auto MyParser = new WavParser();
  if(MyParser->LoadFile(FilePath))
  {
    MyParser->Parser();
  }

  std::cin.get();
  delete MyParser;
  return 0;
}

  • Parser的测试文件

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    enum class TestFileType
{
  //WAVE file, stereo unsigned 8-bit data
    Uint8Stereo,
  //WAVE file, stereo A-law data
    Uint8ALawStereo,
  //WAVE file, stereo µ-law data
    UInt8MuLawStereo,
  //WAVE file, stereo 12/16-bit data
    Int12Stereo,
  //WAVE file, stereo 16-bit data
    Int16Stereo,
  //WAVE file, stereo 24-bit data
    Int24Stereo,
  //WAVE file, stereo 32-bit data
    Int32Stereo,
  //WAVE file, stereo 32-bit float data
    Float32Stereo,
  //WAVE file, stereo 64-bit float data
    Float64Stereo,
  //WAVE (WAVE_FORMAT_EXTENSIBLE) file, stereo unsigned 8-bit data
    Uint8StereoExt,
  //WAVE (WAVE_FORMAT_EXTENSIBLE) file, stereo A-law data
    UInt8ALawStereoExt,
  //WAVE (WAVE_FORMAT_EXTENSIBLE) file, stereo µ-law data
    UInt8MuLawStereoExt,
  //WAVE (WAVE_FORMAT_EXTENSIBLE) file, stereo 12/16-bit data
    Int12StereoExt,
  //WAVE (WAVE_FORMAT_EXTENSIBLE) file, stereo 16-bit data
    Int16StereoExt,
  //WAVE (WAVE_FORMAT_EXTENSIBLE) file, stereo 24-bit data
    Int24StereoExt,
  //WAVE (WAVE_FORMAT_EXTENSIBLE) file, stereo 32-bit data
    Int32StereoExt,
  //WAVE (WAVE_FORMAT_EXTENSIBLE) file, stereo 32-bit float data
    Float32StereoExt,
  //WAVE (WAVE_FORMAT_EXTENSIBLE) file, stereo 64-bit float data
    Float64StereoExt,
  //6-channel WAVE file with speaker locations FL FR FC LF BL BR, 44100 Hz, 16-bit
    Int16Channel_6,
  //8-channel WAVE file with speaker locations FL FR FC LF BL BR - -, 48000 Hz, 24-bit
    Int24Channel_8,
  //WAVE file, BWF Type, 16-bit data
    Int16Bwf,
  //WAVE file, RF64 Type, 24-bit Data
    Int24RF64
};

int main()
{
  const std::string& FilePath = GetTestFilePath(TestFileType::Int16Stereo);

  ......

}
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