From e6697b9de9d765e72c9d399eadf8ed0f03ebf134 Mon Sep 17 00:00:00 2001
From: Trek H <trek.hopton@gmail.com>
Date: Sat, 10 Aug 2019 21:00:26 +0930
Subject: [PATCH] audio-player: added ability to decode consecutive chunks to
 js decoder.

---
 cmd/audio-player/adpcm.js | 69 ++++++++++++++++++++++++---------------
 1 file changed, 42 insertions(+), 27 deletions(-)

diff --git a/cmd/audio-player/adpcm.js b/cmd/audio-player/adpcm.js
index 6767452e..32d66d6b 100644
--- a/cmd/audio-player/adpcm.js
+++ b/cmd/audio-player/adpcm.js
@@ -30,7 +30,7 @@ LICENSE
 const indexTable = [
 	-1, -1, -1, -1, 2, 4, 6, 8,
 	-1, -1, -1, -1, 2, 4, 6, 8
-]
+];
 
 const stepTable = [
 	7, 8, 9, 10, 11, 12, 13, 14,
@@ -45,15 +45,11 @@ const stepTable = [
 	7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
 	15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794,
 	32767
-]
+];
 
 const byteDepth = 2, // We are working with 16-bit samples. TODO(Trek): make configurable.
-	initSamps = 2, // Number of samples used to initialise the encoder.
-	initBytes = initSamps * byteDepth,
-	headBytes = 4, // Number of bytes in the header of ADPCM.
-	samplesPerEnc = 2, // Number of sample encoded at a time eg. 2 16-bit samples get encoded into 1 byte.
-	bytesPerEnc = samplesPerEnc * byteDepth,
-	compFact = 4; // In general ADPCM compresses by a factor of 4.
+	headSize = 8, // Number of bytes in the header of ADPCM.
+	chunkLenSize = 4;
 
 let est = 0, // Estimation of sample based on quantised ADPCM nibble.
 	idx = 0, // Index to step used for estimation.
@@ -93,28 +89,40 @@ function decodeSample(nibble) {
 
 // decode takes an array of bytes of arbitrary length representing adpcm and decodes it into pcm.
 function decode(b) {
-	// Initialize Decoder with first 4 bytes of b.
-	est = bytesToInt16(b[0], b[1]);
-	idx = b[byteDepth];
-	step = stepTable[idx];
+	// Iterate over each chunk and decode it.
+	let chunkLen;
+	var result = [];
+	for (var off = 0; off + headSize <= b.length; off += chunkLen) {
+		// Read length of chunk and check if whole chunk exists.
+		chunkLen = bytesToInt32(b.slice(off, off + chunkLenSize))
+		if (off + chunkLen > b.length) {
+			break;
+		}
+		console.log(b.length, chunkLen, off);
 
-	var result = b.slice(0, 2);
+		// Initialize Decoder with first 4 bytes of b.
+		est = bytesToInt16(b.slice(off + chunkLenSize, off + chunkLenSize + byteDepth));
+		idx = b[off + chunkLenSize + byteDepth];
+		step = stepTable[idx];
 
-	for (var i = headBytes; i < b.length - b[3]; i++) {
-		var twoNibs = b[i];
-		var nib2 = twoNibs >> 4;
-		var nib1 = (nib2 << 4) ^ twoNibs
+		result.push(...b.slice(off + chunkLenSize, off + chunkLenSize + byteDepth));
 
-		var sample1 = int16ToBytes(decodeSample(nib1))
-		result.push(...sample1)
+		for (var i = off + headSize; i < off + chunkLen - b[off + chunkLenSize + 3]; i++) {
+			var twoNibs = b[i];
+			var nib2 = twoNibs >> 4;
+			var nib1 = (nib2 << 4) ^ twoNibs;
 
-		var sample2 = int16ToBytes(decodeSample(nib2))
-		result.push(...sample2)
-	}
-	if (b[3] == 1) {
-		var padNib = b[b.length - 1]
-		var sample = int16ToBytes(decodeSample(padNib))
-		result.push(...sample)
+			var sample1 = int16ToBytes(decodeSample(nib1));
+			result.push(...sample1);
+
+			var sample2 = int16ToBytes(decodeSample(nib2));
+			result.push(...sample2);
+		}
+		if (b[off + chunkLenSize + 3] == 1) {
+			var padNib = b[off + chunkLen - 1];
+			var sample = int16ToBytes(decodeSample(padNib));
+			result.push(...sample);
+		}
 	}
 	return result;
 }
@@ -124,5 +132,12 @@ function int16ToBytes(num) {
 }
 
 function bytesToInt16(b) {
-	return (b[0] | (b[1] << 8))
+	return (b[0] | (b[1] << 8));
+}
+
+function bytesToInt32(b) {
+	return (b[0] |
+		(b[1] << 8) |
+		(b[2] << 16) |
+		(b[3] << 24));
 }
\ No newline at end of file