adpcm: changed adpcm to not have blocks of fixed size

codec/adpcm/adpcm.go

@@ -193,7 +193,7 @@ func (d *decoder) decodeSample(nibble byte) int16 {
 // calcHead sets the state for the encoder by running the first sample through
 // the encoder, and writing the first sample to the encoder's io.Writer (dest).
 // It returns the number of bytes written to the encoder's io.Writer (dest) along with any errors.
-func (e *encoder) calcHead(sample []byte) (int, error) {
+func (e *encoder) calcHead(sample []byte, pad bool) (int, error) {
 	// Check that we are given 1 16-bit sample (2 bytes).
 	const sampSize = 2
 	if len(sample) != sampSize {
@@ -214,7 +214,11 @@ func (e *encoder) calcHead(sample []byte) (int, error) {
 	}
 	n++
 
-	err = e.dest.WriteByte(byte(0x00))
+	if pad {
+		err = e.dest.WriteByte(0x01)
+	} else {
+		err = e.dest.WriteByte(0x00)
+	}
 	if err != nil {
 		return n, err
 	}
@@ -234,7 +238,7 @@ func (e *encoder) encodeBlock(block []byte) (int, error) {
 		return 0, fmt.Errorf("unsupported block size. Given: %v, expected: %v, ie. 505 16-bit PCM samples", len(block), PcmBS)
 	}
 
-	n, err := e.calcHead(block[0:2])
+	n, err := e.calcHead(block[0:2], false)
 	if err != nil {
 		return n, err
 	}
@@ -300,13 +304,19 @@ func (d *decoder) decodeBlock(block []byte) (int, error) {
 // It writes its output to the encoder's dest.
 // The number of bytes written out is returned along with any error that occured.
 func (e *encoder) Write(inPcm []byte) (int, error) {
+	// Determine if there will be a byte that won't contain two full nibbles and will need padding.
+	pcmLen := len(inPcm)
+	pad := false
+	if (pcmLen-2)%4 != 0 {
+		pad = true
+	}
 
-	n, err := e.calcHead(inPcm[0:2])
+	n, err := e.calcHead(inPcm[0:2], pad)
 	if err != nil {
 		return n, err
 	}
 
-	for i := 3; i < len(inPcm); i += 4 {
+	for i := 3; i < pcmLen; i += 4 {
 		nib1 := e.encodeSample(int16(binary.LittleEndian.Uint16(inPcm[i-1 : i+1])))
 		nib2 := e.encodeSample(int16(binary.LittleEndian.Uint16(inPcm[i+1 : i+3])))
 		err = e.dest.WriteByte(byte((nib2 << 4) | nib1))
@@ -315,6 +325,16 @@ func (e *encoder) Write(inPcm []byte) (int, error) {
 		}
 		n++
 	}
+	// If we've reached the end of the pcm data and there's a sample (2 bytes) left over,
+	// compress it to a nibble and leave the first half of the byte padded with 0s.
+	if pad {
+		nib := e.encodeSample(int16(binary.LittleEndian.Uint16(inPcm[pcmLen-2 : pcmLen])))
+		err = e.dest.WriteByte(nib)
+		if err != nil {
+			return n, err
+		}
+		n++
+	}
 
 	return n, nil
 }
@@ -335,7 +355,8 @@ func (d *decoder) Write(inAdpcm []byte) (int, error) {
 
 	// For each byte, seperate it into two nibbles (each nibble is a compressed sample),
 	// then decode each nibble and output the resulting 16-bit samples.
-	for i := 4; i < len(inAdpcm); i++ {
+	// If padding flag is true (Adpcm[3]), only decode up until the last byte, then decode that separately.
+	for i := 4; i < len(inAdpcm)-int(inAdpcm[3]); i++ {
 		twoNibs := inAdpcm[i]
 		nib2 := byte(twoNibs >> 4)
 		nib1 := byte((nib2 << 4) ^ twoNibs)
@@ -356,6 +377,16 @@ func (d *decoder) Write(inAdpcm []byte) (int, error) {
 			return n, err
 		}
 	}
+	if inAdpcm[3] == 0x01 {
+		padNib := inAdpcm[len(inAdpcm)-1]
+		samp := make([]byte, 2)
+		binary.LittleEndian.PutUint16(samp, uint16(d.decodeSample(padNib)))
+		_n, err := d.dest.Write(samp)
+		n += _n
+		if err != nil {
+			return n, err
+		}
+	}
 
 	return n, nil
 }