From: Bill Kelly <billk@...>
Date: 2003-11-09T01:07:13+09:00
Subject: Re: process .wav file?

Hi,

From: "mike re-v" <mrmrmr50@yahoo.com>
>
> Sorry I should have specified linux platform
> I've looked at the RAA several keywd searches
> like 1.) sound i/o
> 2)i/o sound linux
> 3).wav
> I don't see anything relative.

Not sure if this will be of any help, but I wrote some
code awhile back to parse WAV files and read/write the
format chunk (sample rate, etc.) and extract the audio
samples from the WAV...  (Doesn't play the sound, tho!)

For what it's worth I'll attach the code below...

Regards,

Bill


~~ wavtweak.rb ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#
# WAV format info at: http://www.borg.com/~jglatt/tech/wave.htm
# 

class NotRIFFFormat < StandardError; end
class NotWAVEFormat < StandardError; end

def read_chunk_header(file)
  hdr = file.read(8)
  chunkName, chunkLen = hdr.unpack("A4V")
end

def parse_wav(file)
  riff, riffLen = read_chunk_header(file)
  raise NotRIFFFormat unless riff == 'RIFF'
  riffEnd = file.tell + riffLen
  wave = file.read(4)
  raise NotWAVEFormat unless wave == 'WAVE'
  while file.tell < riffEnd
    chunkName, chunkLen = read_chunk_header(file)
    fpos = file.tell
    yield file, chunkName, chunkLen if block_given?
    file.seek(fpos + chunkLen)
  end
end

class WaveFmtChunk
  
  #   short          AudioFormat;   PCM = 1 (i.e. Linear quantization)
  #                                 Values other than 1 indicate some
  #                                 form of compression.
  #   unsigned short NumChannels;   Mono = 1, Stereo = 2, etc.
  #   unsigned long  SampleRate;    8000, 44100, etc.
  #   unsigned long  ByteRate;      == SampleRate * NumChannels * BitsPerSample/8
  #   unsigned short BlockAlign;    == NumChannels * BitsPerSample/8
  #                                 The number of bytes for one sample including
  #                                 all channels.
  #   unsigned short BitsPerSample; 8 bits = 8, 16 bits = 16, etc.

  attr_reader :audioFormat, :numChannels,
              :sampleRate, :byteRate,
              :blockAlign, :bitsPerSample

  PACK_FMT = "vvVVvv"

  def initialize(binRepr)
    @audioFormat, @numChannels,
    @sampleRate, @byteRate,
    @blockAlign, @bitsPerSample = binRepr.unpack(PACK_FMT)
  end
  
  def to_s
    [ @audioFormat, @numChannels,
      @sampleRate, @byteRate,
      @blockAlign, @bitsPerSample ].pack(PACK_FMT)
  end
  
  def set_sample_rate(rate)
    @byteRate = calc_byte_rate(rate)
    @sampleRate = rate
  end
  
  def calc_byte_rate(srate, numch = @numChannels, bitss = @bitsPerSample)
    srate * numch * (bitss / 8)
  end
end

def handle_fmt_chunk(file, chunkLen)
  fmtDatPos = file.tell
  fmt = WaveFmtChunk.new(file.read(chunkLen))
  print "srate is #{fmt.sampleRate} brate is #{fmt.byteRate}\n"
  
  # Tweak the sample rate (without resampling the data)
  #
  # fmt.set_sample_rate(45750)  # (52245)
  # print "srate now #{fmt.sampleRate} brate now #{fmt.byteRate}\n"
  # fs = fmt.to_s
  # print "writing new fmt data, len #{fs.length} bytes "
  # fs.each_byte {|c| printf("%02x", c) }
  # print "\n"
  # file.seek(fmtDatPos)
  # print "cur file ofst #{file.tell}\n"
  # file.write(fmt)
  # print "post write file ofst #{file.tell}\n"
end

def handle_data_chunk(file, chunkLen)
  data = file.read(chunkLen)
end

ARGV.each do |fname|
  puts "#{fname}"
  File.open(fname, File::RDWR) do |f|
    f.binmode
    f.seek(0)
    parse_wav(f) do |file, chunkName, chunkLen|
      puts "'#{chunkName}' size #{chunkLen}"
      case chunkName
        when 'fmt'  then handle_fmt_chunk(file, chunkLen)
        when 'data' then handle_data_chunk(file, chunkLen)
      end
    end
  end
end
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~