Saturday, August 28, 2010

I had always wanted to play and decode the WAVE file properly. I had little success on this using the Microchip's MDD File System in my Project L.A.T.H.I. Recently I came across a wonder full article and am publishing the same for benifit of the readers.

Original Article : https://ccrma.stanford.edu/courses/422/projects/WaveFormat/
Many Thanks to Scott Wilson for his Insight.

The WAVE file format is a subset of Microsoft's RIFF specification for the storage of multimedia files. A RIFF file starts out with a file header followed by a sequence of data chunks. A WAVE file is often just a RIFF file with a single "WAVE" chunk which consists of two sub-chunks -- a "fmt " chunk specifying the data format and a "data" chunk containing the actual sample data. Call this form the "Canonical form".




Offset Size name Description
RIFF Chunk Descriptor
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).
Fmt Sub-Chunk
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. Well, wonder what happens when this number isn't an integer?
34 2 BitsPerSample 8 bits = 8, 16 bits = 16, etc.
(void) 2 ExtraParamSize if PCM, then doesn't exist
(void) X ExtraParams space for extra parameters
Data Sub-Chunk
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. We can also think of this as the size of the read of the subchunk following this number.
44 * Data The actual sound data.

This is the Table Showing the Format Structure with Offset for WAVE File Format.As an example, here are the opening 72 bytes of a WAVE file with bytes shown as hexadecimal numbers:

52 49 46 46 24 08 00 00 57 41 56 45 66 6d 74 20 10 00 00 00 01 00 02 00
22 56 00 00 88 58 01 00 04 00 10 00 64 61 74 61 00 08 00 00 00 00 00 00
24 17 1e f3 3c 13 3c 14 16 f9 18 f9 34 e7 23 a6 3c f2 24 f2 11 ce 1a 0d


Here is the interpretation of these bytes as a WAVE sound file:

 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

References:
1.    http://netghost.narod.ru/gff/graphics/summary/micriff.htm
       RIFF Format Reference (good).

2.    http://www.lightlink.com/tjweber/StripWav/WAVE.html


Content Locations:
1. Canonical Wave File Format Picture
2. Example of Byte Interpretation of the Wave File
3. Word Document Containing the Complete Article

Let me know in case you find any more data on this File Format.

TODO:
- Add the Structure for Reading the Data buffer containing this header info
- Add Code for Generic Interpretation of the data
- Possibly implement in some micro and try to demonstrate as a complete project

Warm Regards,
Boseji

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