audio-player: adpcm file playing in browser

Adpcm files can be uploaded and played however decoding takes a significant time.
The process needs to be optimised.

cmd/audio-player/adpcm.js

@@ -26,12 +26,40 @@ const byteDepth = 2, // We are working with 16-bit samples. TODO(Trek): make con
 	bytesPerEnc = samplesPerEnc * byteDepth,
 	compFact = 4; // In general ADPCM compresses by a factor of 4.
 
-let est, // Estimation of sample based on quantised ADPCM nibble.
-	idx, // Index to step used for estimation.
-	step;
+let est = 0, // Estimation of sample based on quantised ADPCM nibble.
+	idx = 0, // Index to step used for estimation.
+	step = 0;
 
 function decodeSample(nibble) {
-	return new Uint8Array([1, 2])
+
+	let diff = 0;
+	if ((nibble & 4) != 0) {
+		diff += step;
+	}
+	if ((nibble & 2) != 0) {
+		diff += step >> 1;
+	}
+	if ((nibble & 1) != 0) {
+		diff += step >> 2;
+	}
+	diff += step >> 3;
+
+	if ((nibble & 8) != 0) {
+		diff = -diff;
+	}
+	est += diff;
+	idx += indexTable[nibble];
+
+	if (idx < 0) {
+		idx = 0;
+	} else if (idx > stepTable.length - 1) {
+		idx = stepTable.length - 1;
+	}
+
+	step = stepTable[idx];
+
+	result = new Uint8Array(new Uint16Array([est]).buffer);
+	return result;
 }
 
 function decode(b) {
@@ -42,7 +70,7 @@ function decode(b) {
 	}
 
 	// Initialize Decoder with first 4 bytes of b.
-	est = (new Uint16Array(b.slice(0, 2).buffer))[1];
+	est = (new Uint16Array(b.slice(0, 2).buffer))[0];
 	idx = b[byteDepth];
 	step = stepTable[idx];
 
@@ -63,7 +91,6 @@ function decode(b) {
 		var samp = decodeSample(padNib)
 		result = concat(result, samp)
 	}
-
 	return result;
 }
 

cmd/audio-player/main.js

@@ -7,21 +7,16 @@ window.onload = function () {
         reader.onload = event => {
             bytes = new Uint8Array(event.target.result)
 
-            console.log(bytes.slice(0, 16))
-
             var decoded = decode(bytes)
 
             console.log("playing file")
-
-            console.log(decoded.slice(0, 16))
-
-            // var player = new PCMPlayer({
-            //     encoding: '16bitInt',
-            //     channels: 1,
-            //     sampleRate: 48000,
-            //     flushingTime: 2000
-            // });
-            // player.feed(bytes)
+            var player = new PCMPlayer({
+                encoding: '16bitInt',
+                channels: 1,
+                sampleRate: 48000,
+                flushingTime: 2000
+            });
+            player.feed(decoded)
         }
         reader.onerror = error => reject(error)
         reader.readAsArrayBuffer(input)