riff-wave.specs

ears-0.32, linux下有用的语音信号处理工具包

          RIFF Waveform Audio File Format (WAVE) (.WAV)


               This section describes the Waveform format, which is used to
               represent digitized sound.

               The WAVE form is defined as follows. Programs must expect
               (and ignore) any unknown chunks encountered, as with all
               RIFF forms. However, <fmt-ck> must always occur before
               <wave-data>, and both of these chunks are mandatory in a
               WAVE file.

                <WAVE-form> ->
                      RIFF( 'WAVE'
                           <fmt-ck>               // Format
                           [<fact-ck>]                 // Fact chunk
                           [<cue-ck>]             // Cue points
                           [<playlist-ck>]             // Playlist
                           [<assoc-data-list>]              // Associated
                data list
                           <wave-data>   )             // Wave data

               The WAVE chunks are described in the following sections.


          WAVE Format Chunk


               The WAVE format chunk <fmt-ck> specifies the format of the
               <wave-data>. The <fmt-ck> is defined as follows:

                <fmt-ck> ->   fmt( <common-fields>
                                 <format-specific-fields> )

                <common-fields> ->
                      struct
                      {
                         WORD wFormatTag;              // Format category
                         WORD wChannels;          // Number of channels
                         DWORDdwSamplesPerSec;         // Sampling rate
                         DWORDdwAvgBytesPerSec;        // For buffer
                estimation
                         WORD wBlockAlign;        // Data block size
                      }

               The fields in the <common-fields> chunk are as follows:



               Field          Description






               wFormatTag     A number indicating the WAVE format
                              category of the file. The content of
                              the <format-specific-fields> portion
                              of the `fmt' chunk, and the
                              interpretation of the waveform data,
                              depend on this value.

                              You must register any new WAVE format
                              categories. See ``Registering
                              Multimedia Formats'' in Chapter 1,
                              ``Overview of Multimedia
                              Specifications,'' for information on
                              registering WAVE format categories.

                              ``Wave Format Categories,'' following
                              this section, lists the currently
                              defined WAVE format categories.

               wChannels      The number of channels represented in
                              the waveform data, such as 1 for mono
                              or 2 for stereo.

               dwSamplesPerSe The sampling rate (in samples per
               c              second) at which each channel should
                              be played.

               dwAvgBytesPerS The average number of bytes per second
               ec             at which the waveform data should be
                              transferred. Playback software can
                              estimate the buffer size using this
                              value.

               wBlockAlign    The block alignment (in bytes) of the
                              waveform data. Playback software needs
                              to process a multiple of wBlockAlign
                              bytes of data at a time, so the value
                              of wBlockAlign can be used for buffer
                              alignment.



               The <format-specific-fields> consists of zero or more bytes
               of parameters. Which parameters occur depends on the WAVE
               format category-see the following section for details.
               Playback software should be written to allow for (and
               ignore) any unknown <format-specific-fields> parameters that
               occur at the end of this field.



          WAVE Format Categories


               The format category of a WAVE file is specified by the value
               of the wFormatTag field of the `fmt' chunk. The




               representation of data in <wave-data>, and the content of
               the <format-specific-fields> of the `fmt' chunk, depend on
               the format category.

               The currently defined open non-proprietary WAVE format
               categories are as follows:



               wFormatTag Value         Format Category


               WAVE_FORMAT_PCM (0x0001) Microsoft Pulse Code
                                        Modulation (PCM) format



               The following are the registered proprietary WAVE format
               categories:



               wFormatTag Value         Format Category


               IBM_FORMAT_MULAW         IBM mu-law format
               (0x0101)

               IBM_FORMAT_ALAW (0x0102) IBM a-law format

               IBM_FORMAT_ADPCM         IBM AVC Adaptive
               (0x0103)                 Differential Pulse Code
                                        Modulation format



               The following sections describe the Microsoft
               WAVE_FORMAT_PCM format.


               Pulse Code Modulation (PCM) Format


               If the wFormatTag field of the <fmt-ck> is set to
               WAVE_FORMAT_PCM, then the waveform data consists of samples
               represented in pulse code modulation (PCM) format. For PCM
               waveform data, the <format-specific-fields> is defined as
               follows:

                <PCM-format-specific> ->
                      struct
                      {
                         WORD wBitsPerSample;      // Sample size
                      }

               The wBitsPerSample field specifies the number of bits of
               data used to represent each sample of each channel. If there




               are multiple channels, the sample size is the same for each
               channel.

               For PCM data, the wAvgBytesPerSec field of the `fmt' chunk
               should be equal to the following formula rounded up to the
               next whole number:

                                              wBitsPerSample
                 wChannels x wBitsPerSecond x --------------
                                                     8

               The wBlockAlign field should be equal to the following
               formula, rounded to the next whole number:

                             wBitsPerSample
                 wChannels x --------------
                                    8

               Data Packing for PCM WAVE Files

               In a single-channel WAVE file, samples are stored
               consecutively. For stereo WAVE files, channel 0 represents
               the left channel, and channel 1 represents the right
               channel. The speaker position mapping for more than two
               channels is currently undefined. In multiple-channel WAVE
               files, samples are interleaved.

               The following diagrams show the data packing for a 8-bit
               mono and stereo WAVE files:


                     Sample 1     Sample 2     Sample 3    Sample 4


                     Channel 0    Channel 0   Channel 0    Channel 0



                             Data Packing for 8-Bit Mono PCM



                            Sample 1                 Sample 2

                     Channel 0    Channel 1   Channel 0    Channel 0
                      (left)       (right)      (left)      (right)



                            Data Packing for 8-Bit Stereo PCM



               The following diagrams show the data packing for 16-bit mono
               and stereo WAVE files:


                            Sample 1                 Sample 2





                     Channel 0    Channel 0   Channel 0    Channel 0

                     low-order   high-order   low-order   high-order
                       byte         byte         byte        byte


                             Data Packing for 16-Bit Mono PCM



                                        Sample 1

                     Channel 0    Channel 0   Channel 1    Channel 1
                      (left)       (left)      (right)      (right)
                     low-order   high-order   low-order   high-order
                       byte         byte         byte        byte


                            Data Packing for 16-Bit Stereo PCM



               Data Format of the Samples

               Each sample is contained in an integer i. The size of i is
               the smallest number of bytes required to contain the
               specified sample size. The least significant byte is stored
               first. The bits that represent the sample amplitude are
               stored in the most significant bits of i, and the remaining
               bits are set to zero.

               For example, if the sample size (recorded in nBitsPerSample)
               is 12 bits, then each sample is stored in a two-byte
               integer. The least significant four bits of the first (least
               significant) byte is set to zero.

               The data format and maximum and minimums values for PCM
               waveform samples of various sizes are as follows:



               Sample Size  Data Format Maximum Value  Minimum Value


               One to       Unsigned    255 (0xFF)     0
               eight bits   integer

               Nine or      Signed      Largest        Most negative
               more bits    integer i   positive       value of i
                                        value of i


               For example, the maximum, minimum, and midpoint values for
               8-bit and 16-bit PCM waveform data are as follows:






               Format       Maximum     Minimum Value  Midpoint
                            Value                      Value


               8-bit PCM    255 (0xFF)  0              128 (0x80)

               16-bit PCM   32767       -32768         0
                            (0x7FFF)    (-0x8000)


               Examples of PCM WAVE Files

               Example of a PCM WAVE file with 11.025 kHz sampling rate,
               mono, 8 bits per sample:

                RIFF( 'WAVE'     fmt(1, 1, 11025, 11025, 1, 8)
                              data( <wave-data> ) )

               Example of a PCM WAVE file with 22.05 kHz sampling rate,
               stereo, 8 bits per sample:

                RIFF( 'WAVE'     fmt(1, 2, 22050, 44100, 2, 8)
                              data( <wave-data> ) )

               Example of a PCM WAVE file with 44.1 kHz sampling rate,
               mono, 20 bits per sample:

                RIFF( 'WAVE'     INFO(INAM("O Canada"Z))
                              fmt(1, 1, 44100, 132300, 3, 20)
                              data( <wave-data> ) )


          Storage of WAVE Data


               The <wave-data> contains the waveform data. It is defined as
               follows:

                <wave-data> ->   { <data-ck> : <data-list> }

                <data-ck>  ->    data( <wave-data> )

                <wave-list> ->   LIST( 'wavl' {        <data-ck> :
                    // Wave samples
                                           <silence-ck> }... )   // Silence

                <silence-ck> ->  slnt( <dwSamples:DWORD> )       // Count
                of
                                                       // silent samples

               Note:  The `slnt' chunk represents silence, not necessarily
               a repeated zero volume or baseline sample. In 16-bit PCM
               data, if the last sample value played before the silence
               section is a 10000, then if data is still output to the D to
               A converter, it must maintain the 10000 value. If a zero




               value is used, a click may be heard at the start and end of
               the silence section. If play begins at a silence section,
               then a zero value might be used since no other information
               is available. A click might be created if the data following
               the silent section starts with a nonzero value.


          FACT Chunk


               The <fact-ck> fact chunk stores important information about
               the contents of the WAVE file. This chunk is defined as
               follows:

                <fact-ck> -> fact( <dwFileSize:DWORD> )            // Number
                of samples

               The `fact'' chunk is required if the waveform data is
               contained in a `wavl'' LIST chunk and for all compressed