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85 lines
3.4 KiB
Plaintext
85 lines
3.4 KiB
Plaintext
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Sound extraction for CD-DA burning from .WAV audio file format
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Using information and text snippets
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from https://ccrma.stanford.edu/courses/422/projects/WaveFormat/
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in may 2013. The link is now dead. An apparent copy of the page
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is 2017 at: http://soundfile.sapp.org/doc/WaveFormat/
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from https://en.wikipedia.org/wiki/WAV
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For libburnia-project.org by Thomas Schmitt <scdbackup@gmx.net>
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December 2017
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The WAVE file format is an application of the Microsoft RIFF container format
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for multimedia files. A RIFF file consists of Chunks which contain Subchunks.
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The Chunks form a linked list within the file, the Subchunks form a linked
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list inside their Chunk.
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All numbers are stored in little-endian byte order.
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A .WAV file consists at least of one Chunk with id "RIFF", which contains
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one Subchunk with id "fmt " and one with id "data":
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Offset Size Name Description
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0 4 ChunkID Contains the letters "RIFF"
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4 4 ChunkSize The size of the rest of the chunk following
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this field. I.e. the two fields ChunkID and
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ChunkSize are not included in this count.
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8 4 Format Contains the letters "WAVE"
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The "fmt " subchunk describes the sound data's format:
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Offset Size Name Description
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0 4 Subchunk1ID Contains the letters "fmt "
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4 4 Subchunk1Size The size of the rest of the Subchunk following
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this field. I.e. Subchunk1ID and Subchunk1Size
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are not included in this count.
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8 2 AudioFormat PCM = 1 (i.e. Linear quantization)
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Values other than 1 indicate some
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form of compression.
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10 2 NumChannels Mono = 1, Stereo = 2, etc.
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12 4 SampleRate 8000, 44100, etc.
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16 4 ByteRate == SampleRate * NumChannels * BitsPerSample/8
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20 2 BlockAlign == NumChannels * BitsPerSample/8
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The number of bytes for one sample including
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all channels.
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22 2 BitsPerSample 8 bits = 8, 16 bits = 16, etc.
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More data may follow in this Subchunk if AudioFormat is not PCM.
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The "data" subchunk contains the size of the data and the actual sound:
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Offset Size Name Description
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0 4 Subchunk2ID Contains the letters "data"
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4 4 Subchunk2Size == NumSamples * NumChannels * BitsPerSample/8
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The number of audio data bytes.
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8 * Data The audio data bytes.
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CD-DA prescribes these "fmt " parameters:
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AudioFormat == 1
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SampleRate == 44100
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BitsPerSample == 16
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NumChannels == 2 (stereo)
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(little-endian byte order)
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If matching parameters are given in the .WAV file, one can directly use the
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data bytes of Subchunk "data" as payload for burning a CD-DA track.
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Above simple form can be expanded by other Chunks or Subchunks of Chunk "RIFF".
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A .wav file appeared which beared a Subchunk "LIST" inside Chunk "RIFF".
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Wikipedia mentions Chunks "INFO", "CSET", "JUNK", "PAD ".
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Therefore one should expect such Chunks before Chunk "RIFF" and Subchunks
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other than "fmt " and "data" inside the "RIFF" Chunk.
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Multiple Chunks "RIFF" and Subchunks "fmt " or "data" per file have not been
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seen yet. They would make extraction more cumbersome.
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