Provides the ability to write data to a wave file.
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
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.
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
Writerrequires seeking back to the beginning of the file to update information in the file's header.
The sample data format that the file should contain
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 # The position to seek back to when re-writing the header on close @start_pos = @io.pos @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
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
Writer.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
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 writer.close # Does nothing, since Writer is already closed # 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
# File lib/wavefile/writer.rb, line 180 def close return if @closed # 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(@start_pos) 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
Appends the sample data in the given
Buffer to the end of the wave file.
Bufferinstance containing the sample data to be written to the file. The format of the
Bufferdoesn'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.
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 = Writer.new("my_file.wav", Format.new(:stereo, :pcm_16, 44100)) writer.write(buffer) writer.close # This will raise WriterClosedError because the Writer has already been closed. writer.write(buffer)
Returns the number of sample frames that have been written to the file so far.
# File lib/wavefile/writer.rb, line 100 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