class WaveFile::Format

Public: Represents information about the data format for a Wave file, such as number of channels, bits per sample, sample rate, and so forth. A Format instance is used by Reader to indicate what format to read samples out as, and by Writer to indicate what format to write samples as.

Attributes

bits_per_sample[R]

Public: Returns the number of bits per sample, such as 8, 16, 24, 32, or 64.

block_align[R]

Public: Returns the number of bytes in each sample frame. For example, in a 16-bit stereo file, this will be 4 (2 bytes for each 16-bit sample, times 2 channels).

byte_rate[R]

Public: Returns the number of bytes contained in 1 second of sample data. Is equivalent to block_align * sample_rate.

channels[R]

Public: Returns the number of channels, such as 1 or 2. This will always return a Integer, even if the number of channels is specified with a symbol (e.g. :mono) in the constructor.

sample_format[R]

Public: Returns a symbol indicating the sample format, such as :pcm or :float

sample_rate[R]

Public: Returns the number of samples per second, such as 44100.

speaker_mapping[R]

Public: Returns the mapping of each channel to a speaker.

Public Class Methods

new(channels, format_code, sample_rate, speaker_mapping: nil) click to toggle source

Public: Constructs a new immutable Format.

channels - The number of channels in the format. Can either be an Integer

(e.g. 1, 2, 3) or the symbols +:mono+ (equivalent to 1) or
+:stereo+ (equivalent to 2).

format_code - A symbol indicating the format of each sample. Consists of

two parts: a format code, and the bits per sample. The valid
values are +:pcm_8+, +:pcm_16+, +:pcm_24+, +:pcm_32+, +:float_32+,
+:float_64+, and +:float+ (equivalent to +:float_32+)

sample_rate - The number of samples per second, such as 44100 speaker_mapping - An optional array which indicates which speaker each channel should be

mapped to. Each value in the array should be one of these values:

+:front_left+, +:front_right+, +:front_center+, +:low_frequency+, +:back_left+,
+:back_right+, +:front_left_of_center+, +:front_right_of_center+,
+:back_center+, +:side_left+, +:side_right+, +:top_center+, +:top_front_left+,
+:top_front_center+, +:top_front_right+, +:top_back_left+, +:top_back_center+,
+:top_back_right+.

Each value should only appear once, and the channels must follow the ordering above.

For example, <code>[:front_center, :back_left]</code>
is a valid speaker mapping, but <code>[:back_left, :front_center]</code> is not.
If a given channel should not be mapped to a specific speaker, the
value +:undefined+ can be used. If this field is omitted, a default
value for the given number of channels. For example, if there are 2
channels, this will be set to <code>[:front_left, :front_right]</code>.

Examples

format = Format.new(1, :pcm_16, 44100)
format = Format.new(:mono, :pcm_16, 44100)  # Equivalent to above

format = Format.new(:stereo, :float_32, 44100)
format = Format.new(:stereo, :float, 44100)  # Equivalent to above

format = Format.new(2, :pcm_16, 44100, speaker_mapping: [:front_right, :front_center])

# Channels should explicitly not be mapped to particular speakers
# (otherwise, if no speaker_mapping set, it will be set to a default
# value for the number of channels).
format = Format.new(2, :pcm_16, 44100, speaker_mapping: [:undefined, :undefined])

# Will result in InvalidFormatError, because speakers are defined in
# invalid order
format = Format.new(2, :pcm_16, 44100, speaker_mapping: [:front_right, :front_left])

# speaker_mapping will be set to [:front_left, :undefined, :undefined],
# because channels without a speaker mapping will be mapped to :undefined
format = Format.new(3, :pcm_16, 44100, speaker_mapping: [:front_left])

Raises InvalidFormatError if the given arguments are invalid.

# File lib/wavefile/format.rb, line 74
def initialize(channels, format_code, sample_rate, speaker_mapping: nil)
  channels = normalize_channels(channels)

  validate_channels(channels)
  validate_format_code(format_code)
  validate_sample_rate(sample_rate)

  sample_format, bits_per_sample = normalize_format_code(format_code)

  speaker_mapping = normalize_speaker_mapping(channels, speaker_mapping)
  validate_speaker_mapping(channels, speaker_mapping)

  @channels = channels
  @sample_format = sample_format
  @bits_per_sample = bits_per_sample
  @sample_rate = sample_rate
  @block_align = (@bits_per_sample / 8) * @channels
  @byte_rate = @block_align * @sample_rate
  @speaker_mapping = speaker_mapping
end

Public Instance Methods

mono?() click to toggle source

Public: Returns true if the format has 1 channel, false otherwise.

# File lib/wavefile/format.rb, line 96
def mono?
  @channels == 1
end
stereo?() click to toggle source

Public: Returns true if the format has 2 channels, false otherwise.

# File lib/wavefile/format.rb, line 101
def stereo?
  @channels == 2
end

Private Instance Methods

default_speaker_mapping(channels) click to toggle source

Internal

# File lib/wavefile/format.rb, line 179
def default_speaker_mapping(channels)
  # These default mappings determined from these sources:
  #
  # See https://docs.microsoft.com/en-us/windows-hardware/drivers/audio/extensible-wave-format-descriptors
  # This article says to use the `front_center` speaker for mono files when using WAVE_FORMAT_EXTENSIBLE
  #
  # https://msdn.microsoft.com/en-us/library/windows/desktop/dd390971(v=vs.85).aspx
  #
  # https://xiph.org/flac/format.html#frame_header
  if channels == 1  # Mono
    [:front_center]
  elsif channels == 2  # Stereo
    [:front_left, :front_right]
  elsif channels == 3
    [:front_left, :front_right, :front_center]
  elsif channels == 4  # Quad
    [:front_left, :front_right, :back_left, :back_right]
  elsif channels == 5
    [:front_left, :front_right, :front_center, :back_left, :back_right]
  elsif channels == 6  # 5.1
    [:front_left, :front_right, :front_center, :low_frequency, :back_left, :back_right]
  elsif channels == 7
    [:front_left, :front_right, :front_center, :low_frequency, :back_center, :side_left, :side_right]
  elsif channels == 8  # 7.1
    [:front_left, :front_right, :front_center, :low_frequency, :back_left, :back_right, :front_left_of_center, :front_right_of_center]
  elsif channels <= UnvalidatedFormat::SPEAKER_POSITIONS.length
    UnvalidatedFormat::SPEAKER_POSITIONS[0...channels]
  else
    UnvalidatedFormat::SPEAKER_POSITIONS
  end
end
normalize_channels(channels) click to toggle source

Internal

# File lib/wavefile/format.rb, line 141
def normalize_channels(channels)
  if channels == :mono
    return 1
  elsif channels == :stereo
    return 2
  else
    return channels
  end
end
normalize_format_code(format_code) click to toggle source

Internal

# File lib/wavefile/format.rb, line 152
def normalize_format_code(format_code)
  if format_code == :float
    [:float, 32]
  else
    sample_format, bits_per_sample = format_code.to_s.split("_")
    [sample_format.to_sym, bits_per_sample.to_i]
  end
end
normalize_speaker_mapping(channels, speaker_mapping) click to toggle source

Internal

# File lib/wavefile/format.rb, line 162
def normalize_speaker_mapping(channels, speaker_mapping)
  if speaker_mapping.nil?
    speaker_mapping = default_speaker_mapping(channels)
  elsif !speaker_mapping.is_a?(Array)
    return speaker_mapping
  else
    speaker_mapping = speaker_mapping.dup
  end

  if speaker_mapping.length < channels
    speaker_mapping += [:undefined] * (channels - speaker_mapping.length)
  end

  speaker_mapping.freeze
end
validate_channels(candidate_channels) click to toggle source

Internal

# File lib/wavefile/format.rb, line 212
def validate_channels(candidate_channels)
  unless candidate_channels.is_a?(Integer) && VALID_CHANNEL_RANGE === candidate_channels
    raise InvalidFormatError,
          "Invalid number of channels: `#{candidate_channels}`. Must be an Integer between #{VALID_CHANNEL_RANGE.min} and #{VALID_CHANNEL_RANGE.max}."
  end
end
validate_format_code(candidate_format_code) click to toggle source

Internal

# File lib/wavefile/format.rb, line 220
def validate_format_code(candidate_format_code)
  unless SUPPORTED_FORMAT_CODES.include? candidate_format_code
    raise InvalidFormatError,
          "Invalid sample format: `#{candidate_format_code}`. Must be one of: #{SUPPORTED_FORMAT_CODES.inspect}"
  end
end
validate_sample_rate(candidate_sample_rate) click to toggle source

Internal

# File lib/wavefile/format.rb, line 228
def validate_sample_rate(candidate_sample_rate)
  unless candidate_sample_rate.is_a?(Integer) && VALID_SAMPLE_RATE_RANGE === candidate_sample_rate
    raise InvalidFormatError,
          "Invalid sample rate: `#{candidate_sample_rate}`. Must be an Integer between #{VALID_SAMPLE_RATE_RANGE.min} and #{VALID_SAMPLE_RATE_RANGE.max}"
  end
end
validate_speaker_mapping(channels, candidate_speaker_mapping) click to toggle source

Internal

# File lib/wavefile/format.rb, line 236
def validate_speaker_mapping(channels, candidate_speaker_mapping)
  if candidate_speaker_mapping.is_a?(Array) && candidate_speaker_mapping.length == channels
    speaker_mapping_without_invalid_speakers = UnvalidatedFormat::SPEAKER_POSITIONS & candidate_speaker_mapping
    if speaker_mapping_without_invalid_speakers.length < channels
      speaker_mapping_without_invalid_speakers += [:undefined] * (channels - speaker_mapping_without_invalid_speakers.length)
    end

    if speaker_mapping_without_invalid_speakers == candidate_speaker_mapping
      return
    end
  end

  raise InvalidFormatError,
        "Invalid speaker_mapping: `#{candidate_speaker_mapping.inspect}`. Should be an array the same size as the number of channels, containing either :undefined or these known speakers: #{UnvalidatedFormat::SPEAKER_POSITIONS.inspect}. Each defined speaker must come before any of the ones after it in the master list, and all :undefined speakers must come after the last defined speaker."
end