Class: WaveFile::ChunkReaders::FormatChunkReader

Inherits:
BaseChunkReader show all
Defined in:
lib/wavefile/chunk_readers/format_chunk_reader.rb

Overview

Internal

Instance Method Summary collapse

Methods inherited from BaseChunkReader

#raise_error, #read_entire_chunk_body

Constructor Details

#initialize(io, chunk_size) ⇒ FormatChunkReader

:nodoc:



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# File 'lib/wavefile/chunk_readers/format_chunk_reader.rb', line 5

def initialize(io, chunk_size)
  @io = io
  @chunk_size = chunk_size
end

Instance Method Details

#read ⇒ Object 



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# File 'lib/wavefile/chunk_readers/format_chunk_reader.rb', line 10

def read
  if @chunk_size < MINIMUM_CHUNK_SIZE
    raise_error InvalidFormatError, "The format chunk is incomplete; it contains fewer than the required number of fields."
  end

  raw_bytes = read_entire_chunk_body(CHUNK_IDS[:format])

  format_chunk = {}
  format_chunk[:audio_format],
  format_chunk[:channels],
  format_chunk[:sample_rate],
  format_chunk[:byte_rate],
  format_chunk[:block_align],
  format_chunk[:bits_per_sample] = raw_bytes.slice!(0...MINIMUM_CHUNK_SIZE).unpack("vvVVvv")

  if format_chunk[:audio_format] == FORMAT_CODES[:extensible] || (format_chunk[:audio_format] != FORMAT_CODES[:pcm] && @chunk_size > MINIMUM_CHUNK_SIZE)
    if raw_bytes.length < 2
      raise_error InvalidFormatError, "The format chunk is missing an expected extension."
    end

    format_chunk[:extension_size] = raw_bytes.slice!(0...2).unpack(UNSIGNED_INT_16).first

    if format_chunk[:extension_size] > raw_bytes.length
      raise_error InvalidFormatError, "The format chunk extension size of #{format_chunk[:extension_size]} bytes is too large to fit in the format chunk. The format chunk has a stated size of #{@chunk_size} bytes, with #{raw_bytes.length} bytes available for the extension."
    end

    if format_chunk[:audio_format] == FORMAT_CODES[:extensible]
      if format_chunk[:extension_size] < 22
        raise_error InvalidFormatError, "The format chunk extension size of #{format_chunk[:extension_size]} bytes is too small. Since the format chunk has a format code of #{FORMAT_CODES[:extensible]} (i.e. WAVE_FORMAT_EXTENSIBLE), the extension size must be at least 22 bytes."
      end

      format_chunk[:valid_bits_per_sample] = raw_bytes.slice!(0...2).unpack(UNSIGNED_INT_16).first
      format_chunk[:speaker_mapping] = raw_bytes.slice!(0...4).unpack(UNSIGNED_INT_32).first
      format_chunk[:sub_audio_format_guid] = raw_bytes.slice!(0...16)
    end
  end

  UnvalidatedFormat.new(format_chunk)
end