class WaveFile::Writer

Provides the ability to write data to a wave file.

When a Writer is constructed it can be given a block. All samples should be written inside this block, and when the block exits the file will automatically be closed:

Writer.new("my_file.wav", Format.new(:mono, :pcm_16, 44100)) do |writer|
  # Write sample data here
end

If no block is given, you'll need to manually close the Writer when done. The underlaying file will not be valid or playable until close is called.

writer = Writer.new("my_file.wav", Format.new(:mono, :pcm_16, 44100))
# Write sample data here
writer.close

Public

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Attributes

format[R]

Returns

Returns a Format object describing the Wave file being written (number of channels, sample format and bits per sample, sample rate, etc.)

total_sample_frames[R]

Returns

Returns the number of samples (per channel) that have been written to the file so far. For example, if 1000 “left” samples and 1000 “right” samples have been written to a stereo file, this will return 1000.

Public Class Methods

new(io_or_file_name, format) { |self| ... } click to toggle source

Returns

Returns a constructed Writer object which is available for writing sample data to the specified file (via the write method). When all sample data has been written, the Writer should be closed. Note that the wave file being written to will NOT be valid (and playable in other programs) until the Writer has been closed.

If a block is given to this method, sample data can be written inside the given block. When the block terminates, the Writer will be automatically closed (and no more sample data can be written).

If no block is given, then sample data can be written until the close method is called.

io_or_file_name

The name of the wave file to read from, or an open IO object to read from. Only implementations of IO that support seeking are supported, because closing the Writer requires seeking back to the beginning of the file to update information in the file's header.

format

The sample data format that the file should contain

Returns a Writer object that is ready to start writing the specified file's sample data.

# File lib/wavefile/writer.rb, line 39
def initialize(io_or_file_name, format)
  if io_or_file_name.is_a?(String)
    @io = File.open(io_or_file_name, "wb")
    @io_source = :file_name
  else
    @io = io_or_file_name
    @io_source = :io
  end
  @format = format

  @closed = false

  @total_sample_frames = 0
  @pack_code = PACK_CODES[format.sample_format][format.bits_per_sample]

  # Note that the correct sizes for the RIFF and data chunks can't be determined
  # until all samples have been written, so this header as written will be incorrect.
  # When close is called, the correct sizes will be re-written.
  write_header(0)

  if block_given?
    begin
      yield(self)
    ensure
      close
    end
  end
end

Public Instance Methods

close() click to toggle source

Closes the Writer. After a Writer is closed, no more sample data can be written to it.

Note that the wave file will NOT be valid until this method is called. The wave file format requires certain information about the amount of sample data, and this can't be determined until all samples have been written. (This method doesn't need to be called when passing a block to ::new, as this method will automatically be called when the block exits).

If you initialized the Writer with an externally created IO instance, note that the IO instance won't be closed when the Writer is closed. You'll need to manually close the IO yourself. This is on purpose, because the Writer can't know what you may/may not want to do with the IO after closing the Writer.

Examples

square_wave_samples = ([0.5] * 100) + ([-0.5] * 100)
buffer = Buffer.new(square_wave_samples, Format.new(1, :float, 44100))

# Basic example of closing a Writer
writer = Writer.new("my_file.wav", Format.new(:mono, :pcm_16, 44100))
writer.write(buffer)
writer.close

# Closing a Writer writing to an externally opened IO
file = File.open("my_file.wav", "wb")
writer = Writer.new(file, Format.new(:mono, :pcm_16, 44100))
writer.close
# file is still open at this point, so it should be manually closed
file.close

# Trying to write to a Writer that has already been closed
writer = Writer.new("my_file.wav", Format.new(:mono, :pcm_16, 44100))
writer.close
# This will raise WriterClosedError, since the Writer is already closed
writer.write(buffer)

# close() needs to be called for the Wave file to be valid
writer = Writer.new("my_file.wav", Format.new(:mono, :pcm_16, 44100))
writer.write(buffer)
exit
# At this point "my_file.wav" won't be a valid Wave file, because close
# was never called

# But, close() doesn't need to be called when constructing the Writer
# with a block, because it is automatically called when the block exits.
Writer.new("my_file.wav", Format.new(:mono, :pcm_16, 44100)) do |writer|
  writer.write(buffer)
end
# Writer is automatically closed here, because block has exited

Returns

Returns nothing. Has side effect of closing the Writer. Raises WriterClosedError if the Writer is already closed.

# File lib/wavefile/writer.rb, line 173
def close
  if @closed
    raise WriterClosedError
  end

  # The RIFF specification requires that each chunk be aligned to an even number of bytes,
  # even if the byte count is an odd number. Therefore if an odd number of bytes has been
  # written, write an empty padding byte.
  #
  # See http://www-mmsp.ece.mcgill.ca/Documents/AudioFormats/WAVE/Docs/riffmci.pdf, page 11.
  bytes_written = @total_sample_frames * @format.block_align
  if bytes_written.odd?
    @io.write(EMPTY_BYTE)
  end

  # We can't know what chunk sizes to write for the RIFF and data chunks until all
  # samples have been written, so go back to the beginning of the file and re-write
  # those chunk headers with the correct sizes.
  @io.seek(0)
  write_header(@total_sample_frames)

  if @io_source == :file_name
    @io.close
  else
    # If writing to an injected IO instance, seek back to the end of the file, which
    # seems like a more expected place for the position to be than at the end of the
    # header. For example, seeking back to the end allows writing consecutive files
    # to the same IO without overwriting the previous file.
    @io.seek(0, IO::SEEK_END)
  end
  @closed = true
end
closed?() click to toggle source

Returns

Returns true if the Writer is closed, and false if it is open and available for writing.

# File lib/wavefile/writer.rb, line 115
def closed?
  @closed
end
total_duration() click to toggle source

Returns

Returns a Duration instance for the number of sample frames that have been written so far

# File lib/wavefile/writer.rb, line 207
def total_duration
  Duration.new(@total_sample_frames, @format.sample_rate)
end
write(buffer) click to toggle source

Appends the sample data in the given Buffer to the end of the wave file.

buffer

A Buffer instance containing the sample data to be written to the file. The format of the Buffer doesn't have to match the format of the file being written to by the Writer - if it doesn't match, it will automatically be converted to the correct format.

Examples

square_wave_samples = ([0.5] * 100) + ([-0.5] * 100)
buffer = Buffer.new(square_wave_samples, Format.new(1, :float, 44100))

Writer.new("my_file.wav", Format.new(:stereo, :pcm_16, 44100)) do |writer|
  writer.write(buffer)
end

Writer.new("my_file.wav", Format.new(:stereo, :pcm_16, 44100)) do |writer|
  writer.write(buffer)
end
# This will raise WriterClosedError because the Writer has already been closed.
writer.write(buffer)

Returns

Returns the number of sample frames that have been written to the file so far. Raises WriterClosedError if the Writer has been closed. Raises BufferConversionError if the Buffer can't be converted to the Writer's format

# File lib/wavefile/writer.rb, line 94
def write(buffer)
  if @closed
    raise WriterClosedError
  end

  samples = buffer.convert(@format).samples

  if @format.bits_per_sample == 24 && @format.sample_format == :pcm
    samples.flatten.each do |sample|
      @io.write([sample].pack("l<X"))
    end
  else
    @io.write(samples.flatten.pack(@pack_code))
  end

  @total_sample_frames += samples.length
end

Internal

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