Make Waves

makewave.cr

# http://www-mmsp.ece.mcgill.ca/Documents/AudioFormats/WAVE/WAVE.html
# http://soundfile.sapp.org/doc/WaveFormat/

filename = ARGV[0]
filesize = File.size(filename)
puts "Reading #{filename} (#{filesize} bytes)"

# Constant
chunkID = "RIFF"
format = "WAVE"
subchunk1ID = "fmt "
subchunk2ID = "data"
subchunk1Size = 16 # turn into byte representation (10 00 00 00)

# Set
data = File.read(filename).to_slice.to_a
sampleRate = 44100 # turn into 4-byte rep (44 ac 00 00)
bitsPerSample = 16 # turn into 2-byte rep (10 00)
numChannels = 2 # turn into 2-byte rep (02 00)
audioFormat = 1 # turn into 2-byte representation (01 00)

# Calculated
subchunk2Size = filesize # Turn into a bytes representation
chunkSize = 36 + subchunk2Size
byteRate = sampleRate * numChannels * (bitsPerSample / 8)
blockAlign = numChannels * (bitsPerSample / 8)

combined = chunkID.bytes
combined += toBytes(chunkSize, 4)
combined += format.bytes

combined += subchunk1ID.bytes
combined += toBytes(subchunk1Size, 4)
combined += toBytes(audioFormat, 2)
combined += toBytes(numChannels, 2)
combined += toBytes(sampleRate, 4)
combined += toBytes(byteRate, 4)
combined += toBytes(blockAlign, 2)
combined += toBytes(bitsPerSample, 2)

combined += subchunk2ID.bytes
combined += toBytes(subchunk2Size, 4)
combined += data

content = Slice.new(combined.to_unsafe, combined.size)
File.write("#{filename}.wav", content, mode: "w")

def toBytes(num, numBytes)
	bytes = num.to_s(16)
	bytes = bytes.size % 2 == 0 ? bytes : "0#{bytes}"
	bytes = bytes.split(/(.{2})/)
	bytes.delete("")
	bytes.map!{|c| c.size != 2 ? "0#{c}" : c}
	bytes.reverse!
	while bytes.size < numBytes
		bytes.push("00")
	end
	bytes.map{|c| c.hexbytes[0] }
end