mirror of https://bitbucket.org/ausocean/av.git
audio-player: structured Decoder as a class
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Trek H
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0517e399d1
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7f2c77368d
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@ -27,121 +27,129 @@ LICENSE
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Reference algorithms for ADPCM compression and decompression are in part 6.
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*/
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// Table of index changes (see spec).
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const indexTable = [
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-1, -1, -1, -1, 2, 4, 6, 8,
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-1, -1, -1, -1, 2, 4, 6, 8
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];
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// Quantize step size table (see spec).
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const stepTable = [
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7, 8, 9, 10, 11, 12, 13, 14,
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16, 17, 19, 21, 23, 25, 28, 31,
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34, 37, 41, 45, 50, 55, 60, 66,
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73, 80, 88, 97, 107, 118, 130, 143,
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157, 173, 190, 209, 230, 253, 279, 307,
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337, 371, 408, 449, 494, 544, 598, 658,
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724, 796, 876, 963, 1060, 1166, 1282, 1411,
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1552, 1707, 1878, 2066, 2272, 2499, 2749, 3024,
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3327, 3660, 4026, 4428, 4871, 5358, 5894, 6484,
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7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
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15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794,
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32767
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];
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const byteDepth = 2; // We are working with 16-bit samples. TODO(Trek): make configurable.
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const headSize = 8; // Number of bytes in the header of ADPCM.
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const chunkLenSize = 4;
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let est = 0; // Estimation of sample based on quantised ADPCM nibble.
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let idx = 0; // Index to step used for estimation.
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let step = 0;
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// decodeSample takes 4 bits which represents a single ADPCM nibble, and returns a 16 bit decoded PCM sample.
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function decodeSample(nibble) {
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let diff = 0;
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if ((nibble & 4) != 0) {
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diff += step;
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}
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if ((nibble & 2) != 0) {
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diff += step >> 1;
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}
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if ((nibble & 1) != 0) {
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diff += step >> 2;
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}
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diff += step >> 3;
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if ((nibble & 8) != 0) {
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diff = -diff;
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}
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est += diff;
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idx += indexTable[nibble];
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if (idx < 0) {
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idx = 0;
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} else if (idx > stepTable.length - 1) {
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idx = stepTable.length - 1;
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class Decoder {
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constructor() {
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this.est = 0; // Estimation of sample based on quantised ADPCM nibble.
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this.idx = 0; // Index to step used for estimation.
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this.step = 0;
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}
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step = stepTable[idx];
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// Table of index changes (see spec).
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static get indexTable() {
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return [
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-1, -1, -1, -1, 2, 4, 6, 8,
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-1, -1, -1, -1, 2, 4, 6, 8
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];
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}
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result = est;
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return result;
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}
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// Quantize step size table (see spec).
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static get stepTable() {
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return [
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7, 8, 9, 10, 11, 12, 13, 14,
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16, 17, 19, 21, 23, 25, 28, 31,
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34, 37, 41, 45, 50, 55, 60, 66,
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73, 80, 88, 97, 107, 118, 130, 143,
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157, 173, 190, 209, 230, 253, 279, 307,
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337, 371, 408, 449, 494, 544, 598, 658,
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724, 796, 876, 963, 1060, 1166, 1282, 1411,
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1552, 1707, 1878, 2066, 2272, 2499, 2749, 3024,
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3327, 3660, 4026, 4428, 4871, 5358, 5894, 6484,
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7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
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15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794,
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32767
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];
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}
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// decode takes an array of bytes of arbitrary length representing adpcm and decodes it into pcm.
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function decode(b) {
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// Iterate over each chunk and decode it.
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let chunkLen;
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let result = [];
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for (let off = 0; off + headSize <= b.length; off += chunkLen) {
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// Read length of chunk and check if whole chunk exists.
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chunkLen = bytesToInt32(b.slice(off, off + chunkLenSize))
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if (off + chunkLen > b.length) {
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break;
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static get byteDepth() { return 2; } // We are working with 16-bit samples. TODO(Trek): make configurable.
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static get headSize() { return 8; } // Number of bytes in the header of ADPCM.
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static get chunkLenSize() { return 4; }
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// decodeSample takes 4 bits which represents a single ADPCM nibble, and returns a 16 bit decoded PCM sample.
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decodeSample(nibble) {
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let diff = 0;
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if ((nibble & 4) != 0) {
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diff += this.step;
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}
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if ((nibble & 2) != 0) {
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diff += this.step >> 1;
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}
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if ((nibble & 1) != 0) {
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diff += this.step >> 2;
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}
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diff += this.step >> 3;
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if ((nibble & 8) != 0) {
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diff = -diff;
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}
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this.est += diff;
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this.idx += Decoder.indexTable[nibble];
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if (this.idx < 0) {
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this.idx = 0;
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} else if (this.idx > Decoder.stepTable.length - 1) {
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this.idx = Decoder.stepTable.length - 1;
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}
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// Initialize Decoder with first 4 bytes of b.
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est = bytesToInt16(b.slice(off + chunkLenSize, off + chunkLenSize + byteDepth));
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idx = b[off + chunkLenSize + byteDepth];
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step = stepTable[idx];
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this.step = Decoder.stepTable[this.idx];
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result.push(...b.slice(off + chunkLenSize, off + chunkLenSize + byteDepth));
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for (let i = off + headSize; i < off + chunkLen - b[off + chunkLenSize + 3]; i++) {
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let twoNibs = b[i];
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let nib2 = twoNibs >> 4;
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let nib1 = (nib2 << 4) ^ twoNibs;
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let sample1 = int16ToBytes(decodeSample(nib1));
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result.push(...sample1);
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let sample2 = int16ToBytes(decodeSample(nib2));
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result.push(...sample2);
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}
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if (b[off + chunkLenSize + 3] == 1) {
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let padNib = b[off + chunkLen - 1];
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let sample = int16ToBytes(decodeSample(padNib));
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result.push(...sample);
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}
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return this.est;
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}
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return result;
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}
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// int16ToBytes takes a number assumed to be an int 16 and converts it to an array containing bytes (Little Endian).
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function int16ToBytes(num) {
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return [(num & 0x00ff), (num & 0xff00) >> 8];
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}
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// decode takes an array of bytes of arbitrary length representing adpcm and decodes it into pcm.
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decode(b) {
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// Iterate over each chunk and decode it.
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let chunkLen;
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let result = [];
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for (let off = 0; off + Decoder.headSize <= b.length; off += chunkLen) {
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// Read length of chunk and check if whole chunk exists.
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chunkLen = Decoder.bytesToInt32(b.slice(off, off + Decoder.chunkLenSize))
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if (off + chunkLen > b.length) {
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break;
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}
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// 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.
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function bytesToInt16(b) {
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return (b[0] | (b[1] << 8));
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}
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// Initialize Decoder with first 4 bytes of b.
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this.est = Decoder.bytesToInt16(b.slice(off + Decoder.chunkLenSize, off + Decoder.chunkLenSize + Decoder.byteDepth));
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this.idx = b[off + Decoder.chunkLenSize + Decoder.byteDepth];
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this.step = Decoder.stepTable[this.idx];
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// bytesToInt32 takes an array of bytes (assumed to be values between 0 and 255), interprates them as little endian and converts it to an int32.
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function bytesToInt32(b) {
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return (b[0] |
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(b[1] << 8) |
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(b[2] << 16) |
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(b[3] << 24));
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result.push(...b.slice(off + Decoder.chunkLenSize, off + Decoder.chunkLenSize + Decoder.byteDepth));
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for (let i = off + Decoder.headSize; i < off + chunkLen - b[off + Decoder.chunkLenSize + 3]; i++) {
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let twoNibs = b[i];
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let nib2 = twoNibs >> 4;
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let nib1 = (nib2 << 4) ^ twoNibs;
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let sample1 = Decoder.int16ToBytes(this.decodeSample(nib1));
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result.push(...sample1);
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let sample2 = Decoder.int16ToBytes(this.decodeSample(nib2));
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result.push(...sample2);
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}
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if (b[off + Decoder.chunkLenSize + 3] == 1) {
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let padNib = b[off + chunkLen - 1];
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let sample = Decoder.int16ToBytes(this.decodeSample(padNib));
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result.push(...sample);
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}
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}
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return result;
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}
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// int16ToBytes takes a number assumed to be an int 16 and converts it to an array containing bytes (Little Endian).
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static int16ToBytes(num) {
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return [(num & 0x00ff), (num & 0xff00) >> 8];
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}
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// 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.
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static bytesToInt16(b) {
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return (b[0] | (b[1] << 8));
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}
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// bytesToInt32 takes an array of bytes (assumed to be values between 0 and 255), interprates them as little endian and converts it to an int32.
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static bytesToInt32(b) {
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return (b[0] |
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(b[1] << 8) |
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(b[2] << 16) |
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(b[3] << 24));
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}
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}
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@ -31,11 +31,13 @@ function playFile() {
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reader.onload = event => {
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bytes = new Uint8Array(event.target.result)
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let dec = new Decoder();
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// Decode adpcm to pcm.
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var decoded = decode(Array.from(bytes))
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let decoded = dec.decode(Array.from(bytes))
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// Convert raw pcm to wav TODO(Trek): make these configurable.
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var wav = pcmToWav(decoded, 48000, 1, 16);
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let wav = pcmToWav(decoded, 48000, 1, 16);
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// Play wav data in player.
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const blob = new Blob([Uint8Array.from(wav)], {
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@ -57,8 +59,8 @@ function playFile() {
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// getQuery gets everything after the question mark in the URL.
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function getQuery() {
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var regex = new RegExp("\\?(.*)");
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var match = regex.exec(window.location.href);
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let regex = new RegExp("\\?(.*)");
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let match = regex.exec(window.location.href);
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if (match == null) {
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return '';
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} else {
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@ -68,7 +70,7 @@ function getQuery() {
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// load gets the file from the given url and displays a link for download.
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function load() {
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var url = document.getElementById('url').value;
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let url = document.getElementById('url').value;
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if (url == "") {
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url = getQuery()
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document.getElementById('url').value = url;
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@ -80,7 +82,7 @@ function load() {
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return;
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}
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var request = new XMLHttpRequest();
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let request = new XMLHttpRequest();
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request.responseType = "blob";
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request.onreadystatechange = function () {
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if (request.readyState === XMLHttpRequest.DONE) {
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@ -91,7 +93,7 @@ function load() {
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dataURL = URL.createObjectURL(data);
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var link = document.getElementById("link");
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let link = document.getElementById("link");
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link.href = dataURL;
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link.download = "media.ts";
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link.innerHTML = "Download";
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