GetWaveInfo
If you've ever wondered how sound applications can show the kilohertz and samples per second
information about a waveform file (.WAV), the answer lies in the RIFF file format.
The RIFF file format is designed to be as generic as possible. It is used for waveform, AVI, palette,
and other information standards that may need to be mixed and used together. Generally speaking,
though, any file with a WAV extension will only contain waveform data.
RIFF provides information in chunks and subchunks. The header for each chunk describes the
length of the chunk and the type of data the chunk contains (WAVE, for instance, is the string
identifying a WAVE chunk).
The Wave subchunk is immediately followed by the WAVE Format Chunk. It is this small chunk
that defines the structure of the waveform data that will follow. It defines the format of the
waveform, the number of channels used (with 0 being mono, 1 being stereo), the sampling rate, the
kilohertz at which is was recorded, and the data block size. Of these, only mono/stereo and the
sampling rate are likely to be of interest unless you intend to write your own custom waveform
player.
Original Author: Tims VB 5 tips and tricks
Assumptions
had originally defined all of the string chunk identifiers (RIFF, WAVE, and 'fmt ') as being strings
in our user-defined data type WavInfo. But as fate would have it, I kept getting 'Bad File Handle'
errors when I used the string data types with VB5.0. So I elected to use a rather lengthy binary
representation of the same information, which follows the BUG FIX comment. I suspect that it has
something to do with Unicode, but really don't care to chase it down.
API Declarations
'Type n, Mono/Stereo, 8/16 bit sample
'These constants are not used internally, and
'can be safely deleted if you do not intend to use them
Public Const WAVE_FORMAT_1M08 = &H1
Public Const WAVE_FORMAT_1M16 = &H4
Public Const WAVE_FORMAT_1S08 = &H2
Public Const WAVE_FORMAT_1S16 = &H8
Public Const WAVE_FORMAT_2M08 = &H10
Public Const WAVE_FORMAT_2M16 = &H40
Public Const WAVE_FORMAT_2S08 = &H20
Public Const WAVE_FORMAT_2S16 = &H80
Public Const WAVE_FORMAT_4M08 = &H100
Public Const WAVE_FORMAT_4M16 = &H400
Public Const WAVE_FORMAT_4S08 = &H200
Public Const WAVE_FORMAT_4S16 = &H800
'BUG FIX
'Binary representations of strings
Public Const RIFF_ID = 1179011410
Public Const RIFF_WAVE = 1163280727
Public Const RIFF_FMT = 544501094
'Typical header of a simple RIFF WAVE file
Public Type WAVInfo
Riff_Format As Long
chunk_size As Long
ChunkID As Long
fmt As Long
Wave_Format As Integer
Channels As Integer '0 = mono, 1 = stereo
SamplesPerSecond As Long
AverageBytesPerSecond As Long '11.025kHz, 22.05kHz, etc
BlockAlign As Integer 'Size of blocks for low level playback
End Type
Code
Public Function GetWaveInfo(Byval filename As String, Byref w As WAVInfo) _
As Boolean
Dim ff As Integer
ff = FreeFile
On Error GoTo ehandler
Open filename For Binary Access Read As #ff
On Error GoTo ehandler_fo
Get #ff, , w
Close #ff
On Error GoTo ehandler
If w.Riff_Format = RIFF_ID And w.ChunkID = _
RIFF_WAVE And w.fmt = RIFF_FMT Then
GetWaveInfo = True
Else
GetWaveInfo = False
End If
Exit Function
ehandler_fo:
Close #ff
ehandler:
GetWaveInfo = False
End Function
Loading Comments ...
Comments
No comments have been added for this post.
You must be logged in to make a comment.