WAVE PCM soundfile format-优快云博客

本文链接：https://blog.youkuaiyun.com/ckbulesky/article/details/14226175

本文详细解析了WAVE PCM格式的基本构成，包括RIFF头部、格式标识、子块描述等关键部分，以及如何理解8位和16位样本存储方式。

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WAVE PCM 格式分析：

The canonical WAVE format starts with the RIFF header:

0         4   ChunkID          Contains the letters "RIFF" in ASCII form
                               (0x52494646 big-endian form).
4         4   ChunkSize        36 + SubChunk2Size, or more precisely:
                               4 + (8 + SubChunk1Size) + (8 + SubChunk2Size)
                               This is the size of the rest of the chunk 
                               following this number.  This is the size of the 
                               entire file in bytes minus 8 bytes for the
                               two fields not included in this count:
                               ChunkID and ChunkSize.
8         4   Format           Contains the letters "WAVE"
                               (0x57415645 big-endian form).

The "WAVE" format consists of two subchunks: "fmt " and "data":
The "fmt " subchunk describes the sound data's format:

12        4   Subchunk1ID      Contains the letters "fmt "
                               (0x666d7420 big-endian form).
16        4   Subchunk1Size    16 for PCM.  This is the size of the
                               rest of the Subchunk which follows this number.
20        2   AudioFormat      PCM = 1 (i.e. Linear quantization)
                               Values other than 1 indicate some 
                               form of compression.
22        2   NumChannels      Mono = 1, Stereo = 2, etc.
24        4   SampleRate       8000, 44100, etc.
28        4   ByteRate         == SampleRate * NumChannels * BitsPerSample/8
32        2   BlockAlign       == NumChannels * BitsPerSample/8
                               The number of bytes for one sample including
                               all channels. I wonder what happens when
                               this number isn't an integer?
34        2   BitsPerSample    8 bits = 8, 16 bits = 16, etc.
          2   ExtraParamSize   if PCM, then doesn't exist
          X   ExtraParams      space for extra parameters

The "data" subchunk contains the size of the data and the actual sound:

36        4   Subchunk2ID      Contains the letters "data"
                               (0x64617461 big-endian form).
40        4   Subchunk2Size    == NumSamples * NumChannels * BitsPerSample/8
                               This is the number of bytes in the data.
                               You can also think of this as the size
                               of the read of the subchunk following this 
                               number.
44        *   Data             The actual sound data.

看以下例子分析：

Notes:

The default byte ordering assumed for WAVE data files is little-endian. Files written using the big-endian byte ordering scheme have the identifier RIFX instead of RIFF.
The sample data must end on an even byte boundary. Whatever that means.
8-bit samples are stored as unsigned bytes, ranging from 0 to 255. 16-bit samples are stored as 2's-complement signed integers, ranging from -32768 to 32767.
There may be additional subchunks in a Wave data stream. If so, each will have a char[4] SubChunkID, and unsigned long SubChunkSize, and SubChunkSize amount of data.
RIFF stands for Resource Interchange File Format.

General discussion of RIFF files:

Multimedia applications require the storage and management of a wide variety of data, including bitmaps, audio data, video data, and peripheral device control information. RIFF provides a way to store all these varied types of data. The type of data a RIFF file contains is indicated by the file extension. Examples of data that may be stored in RIFF files are:

Audio/visual interleaved data (.AVI)
Waveform data (.WAV)
Bitmapped data (.RDI)
MIDI information (.RMI)
Color palette (.PAL)
Multimedia movie (.RMN)
Animated cursor (.ANI)
A bundle of other RIFF files (.BND)

NOTE: At this point, AVI files are the only type of RIFF files that have been fully implemented using the current RIFF specification. Although WAV files have been implemented, these files are very simple, and their developers typically use an older specification in constructing them.

For more info see http://www.ora.com/centers/gff/formats/micriff/index.htm