audio-player: using typed arrays

change decoder to use typed array and array indexing instead of pushing to regular arrays for performance reasons.

cmd/audio-player/adpcm.js

@@ -61,7 +61,7 @@ class Decoder {
         ];
     }
 
-    static get byteDepth() { return 2; }    // We are working with 16-bit samples. TODO(Trek): make configurable.
+    static get byteDepth() { return 2; }    // We are working with 16-bit samples.
     static get headSize() { return 8; }     // Number of bytes in the header of ADPCM.
     static get chunkLenSize() { return 4; } // Length in bytes of the chunk length field in header.
     static get compFact() { return 4; }     // In general ADPCM compresses by a factor of 4.
@@ -99,9 +99,10 @@ class Decoder {
 
     // decode takes an array of bytes of arbitrary length representing adpcm and decodes it into pcm.
     decode(b) {
+        let result = new Uint16Array(Decoder.decBytes(b)/Decoder.byteDepth);
+        let resultOff = 0;
         // Iterate over each chunk and decode it.
         let chunkLen;
-        let result = [];
         for (let off = 0; off + Decoder.headSize <= b.length; off += chunkLen) {
             // Read length of chunk and check if whole chunk exists.
             chunkLen = Decoder.bytesToInt32(b.slice(off, off + Decoder.chunkLenSize))
@@ -109,38 +110,37 @@ class Decoder {
                 break;
             }
 
-            // Initialize Decoder with first 4 bytes of b.
+            // Initialize Decoder.
             this.est = Decoder.bytesToInt16(b.slice(off + Decoder.chunkLenSize, off + Decoder.chunkLenSize + Decoder.byteDepth));
             this.idx = b[off + Decoder.chunkLenSize + Decoder.byteDepth];
             this.step = Decoder.stepTable[this.idx];
 
-            result.push(...b.slice(off + Decoder.chunkLenSize, off + Decoder.chunkLenSize + Decoder.byteDepth));
+            result[resultOff] = Decoder.bytesToInt16(b.slice(off + Decoder.chunkLenSize, off + Decoder.chunkLenSize + Decoder.byteDepth));
+            resultOff++;
 
             for (let i = off + Decoder.headSize; i < off + chunkLen - b[off + Decoder.chunkLenSize + 3]; i++) {
                 let twoNibs = b[i];
                 let nib2 = twoNibs >> 4;
                 let nib1 = (nib2 << 4) ^ twoNibs;
 
-                let sample1 = Decoder.int16ToBytes(this.decodeSample(nib1));
+                let sample1 = this.decodeSample(nib1);
-                result.push(...sample1);
+                result[resultOff] = sample1;
+                resultOff++;
                 
-                let sample2 = Decoder.int16ToBytes(this.decodeSample(nib2));
+                let sample2 = this.decodeSample(nib2);
-                result.push(...sample2);
+                result[resultOff] = sample2;
+                resultOff++;
             }
             if (b[off + Decoder.chunkLenSize + 3] == 1) {
                 let padNib = b[off + chunkLen - 1];
-                let sample = Decoder.int16ToBytes(this.decodeSample(padNib));
+                let sample = this.decodeSample(padNib);
-                result.push(...sample);
+                result[resultOff] = sample;
+                resultOff++;
             }
         }
         return result;
     }
 
-    // int16ToBytes takes a number assumed to be an int 16 and converts it to an array containing bytes (Little Endian).
-    static int16ToBytes(num) {
-        return [(num & 0x00ff), (num & 0xff00) >> 8];
-    }
-
     // bytesToInt16 takes an array of bytes (assumed to be values between 0 and 255), interprates them as little endian and converts it to an int16.
     static bytesToInt16(b) {
         return (b[0] | (b[1] << 8));

cmd/audio-player/main.js

@@ -29,18 +29,18 @@ function playFile() {
     const reader = new FileReader()
 
     reader.onload = event => {
-        bytes = new Uint8Array(event.target.result)
+        bytes = new Uint8Array(event.target.result);
 
         let dec = new Decoder();
 
         // Decode adpcm to pcm.
-        let decoded = dec.decode(Array.from(bytes))
+        let decoded = dec.decode(bytes);
 
         // Convert raw pcm to wav TODO(Trek): make these configurable.
-        let wav = pcmToWav(decoded, 48000, 1, 16);
+        let wav = pcmToWav(new Uint8Array(decoded.buffer), 48000, 1, 16);
 
         // Play wav data in player.
-        const blob = new Blob([Uint8Array.from(wav)], {
+        const blob = new Blob([wav], {
             type: 'audio/wav'
         });
         const url = URL.createObjectURL(blob);

cmd/audio-player/pcm-to-wav.js

@@ -24,41 +24,74 @@ LICENSE
 
 // pcmToWav takes raw pcm data along with the sample rate, number of channels and bit-depth, 
 // and adds a WAV header to it so that it can be read and played by common players.
-// Input and output data bytes are represented as arrays of 8 bit integers.
+// Input should be a Uint16Array containing 16 bit PCM samples, output will be a Uint8Array representing the bytes of the wav file.
 // WAV spec.: http://soundfile.sapp.org/doc/WaveFormat/
 function pcmToWav(data, rate, channels, bitdepth) {
-    subChunk2ID = [100, 97, 116, 97]; // "data".
+    let subChunk2ID = [100, 97, 116, 97]; // "data".
-    subChunk2Size = int32ToBytes(data.length);
+    let subChunk2Size = int32ToBytes(data.length);
 
-    subChunk1ID = [102, 109, 116, 32]; // "fmt ".
+    let subChunk1ID = [102, 109, 116, 32]; // "fmt ".
-    subChunk1Size = int32ToBytes(16);
+    let subChunk1Size = int32ToBytes(16);
-    audioFmt = int16ToBytes(1); // 1 = PCM.
+    let audioFmt = int16ToBytes(1); // 1 = PCM.
-    numChannels = int16ToBytes(channels);
+    let numChannels = int16ToBytes(channels);
-    sampleRate = int32ToBytes(rate);
+    let sampleRate = int32ToBytes(rate);
-    byteRate = int32ToBytes(rate * channels * bitdepth / 8);
+    let byteRate = int32ToBytes(rate * channels * bitdepth / 8);
-    blockAlign = int16ToBytes(channels * bitdepth / 8);
+    let blockAlign = int16ToBytes(channels * bitdepth / 8);
-    bitsPerSample = int16ToBytes(bitdepth)
+    let bitsPerSample = int16ToBytes(bitdepth)
 
-    chunkID = [82, 73, 70, 70]; // "RIFF".
+    let chunkID = [82, 73, 70, 70]; // "RIFF".
-    chunkSize = int32ToBytes(36 + data.length);
+    let chunkSize = int32ToBytes(36 + data.length);
-    format = [87, 65, 86, 69]; // "WAVE".
+    let format = [87, 65, 86, 69]; // "WAVE".
 
-    result = chunkID;
+    let result = new Uint8Array((data.length*2) + 44);
-    result.push(...chunkSize, ...format, ...subChunk1ID, ...subChunk1Size, ...audioFmt, ...numChannels, ...sampleRate, ...byteRate, ...blockAlign, ...bitsPerSample, ...subChunk2ID, ...subChunk2Size);
+    let off = 0;
-    return result.concat(data);
+
+    result.set(chunkID, off);
+    off += 4;
+    result.set(chunkSize, off);
+    off += 4;
+    result.set(format, off);
+    off += 4;
+    result.set(subChunk1ID, off);
+    off += 4;
+    result.set(subChunk1Size, off);
+    off += 4;
+    result.set(audioFmt, off);
+    off += 2;
+    result.set(numChannels, off);
+    off += 2;
+    result.set(sampleRate, off);
+    off += 4;
+    result.set(byteRate, off);
+    off += 4;
+    result.set(blockAlign, off);
+    off += 2;
+    result.set(bitsPerSample, off);
+    off += 2;
+    result.set(subChunk2ID, off);
+    off += 4;
+    result.set(subChunk2Size, off);
+    off += 4;
+
+    result.set(data, off);
+
+    return result;
 }
 
 // int32ToBytes takes a number assumed to be an int 32 and converts it to an array containing bytes (Little Endian).
 function int32ToBytes(num) {
-    return [
+    let b = new Uint8Array(4);
-        (num & 0x000000ff),
+    b[0] = (num & 0x000000ff);
-        (num & 0x0000ff00) >> 8,
+    b[1] = (num & 0x0000ff00) >> 8;
-        (num & 0x00ff0000) >> 16,
+    b[2] = (num & 0x00ff0000) >> 16;
-        (num & 0xff000000) >> 24
+    b[3] = (num & 0xff000000) >> 24;
-    ];
+    return b;
 }
 
 // int16ToBytes takes a number assumed to be an int 16 and converts it to an array containing bytes (Little Endian).
 function int16ToBytes(num) {
-    return [(num & 0x00ff), (num & 0xff00) >> 8];
+    let b = new Uint8Array(2);
+    b[0] = (num & 0x00ff);
+    b[1] = (num & 0xff00) >> 8;
+    return b;
 }