Class: WaveFile::Format

Inherits:
Object
  • Object
show all
Defined in:
lib/wavefile/format.rb

Overview

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.

This class is immutable - once a new Format is constructed, it can’t be modified.

Direct Known Subclasses

UnvalidatedFormat

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(channels, format_code, sample_rate, speaker_mapping: nil) ⇒ Format

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, [:front_center, :back_left]
is a valid speaker mapping, but [:back_left, :front_center] 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 [:front_left, :front_right].

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.



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# File 'lib/wavefile/format.rb', line 72

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

Instance Attribute Details

#bits_per_sample ⇒ Object (readonly)

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



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# File 'lib/wavefile/format.rb', line 112

def bits_per_sample
  @bits_per_sample
end

#block_align ⇒ Object (readonly)

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).



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# File 'lib/wavefile/format.rb', line 119

def block_align
  @block_align
end

#byte_rate ⇒ Object (readonly)

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



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# File 'lib/wavefile/format.rb', line 123

def byte_rate
  @byte_rate
end

#channels ⇒ Object (readonly)

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.



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# File 'lib/wavefile/format.rb', line 106

def channels
  @channels
end

#sample_format ⇒ Object (readonly)

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



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# File 'lib/wavefile/format.rb', line 109

def sample_format
  @sample_format
end

#sample_rate ⇒ Object (readonly)

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



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# File 'lib/wavefile/format.rb', line 115

def sample_rate
  @sample_rate
end

#speaker_mapping ⇒ Object (readonly)

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



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# File 'lib/wavefile/format.rb', line 126

def speaker_mapping
  @speaker_mapping
end

Instance Method Details

#mono? ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/wavefile/format.rb', line 94

def mono?
  @channels == 1
end

#stereo? ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/wavefile/format.rb', line 99

def stereo?
  @channels == 2
end