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audio-player: added ability to decode consecutive chunks to js decoder.

This commit is contained in:
Trek H 2019-08-10 21:00:26 +09:30
parent d23ae1a290
commit e6697b9de9
1 changed files with 42 additions and 27 deletions
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69
cmd/audio-player/adpcm.js
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@ -30,7 +30,7 @@ LICENSE
const indexTable = [ const indexTable = [
-1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8,
-1, -1, -1, -1, 2, 4, 6, 8 -1, -1, -1, -1, 2, 4, 6, 8
] ];
const stepTable = [ const stepTable = [
7, 8, 9, 10, 11, 12, 13, 14, 7, 8, 9, 10, 11, 12, 13, 14,
@ -45,15 +45,11 @@ const stepTable = [
7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794,
32767 32767
] ];
const byteDepth = 2, // We are working with 16-bit samples. TODO(Trek): make configurable. const byteDepth = 2, // We are working with 16-bit samples. TODO(Trek): make configurable.
initSamps = 2, // Number of samples used to initialise the encoder. headSize = 8, // Number of bytes in the header of ADPCM.
initBytes = initSamps * byteDepth, chunkLenSize = 4;
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.
let est = 0, // Estimation of sample based on quantised ADPCM nibble. let est = 0, // Estimation of sample based on quantised ADPCM nibble.
idx = 0, // Index to step used for estimation. 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. // decode takes an array of bytes of arbitrary length representing adpcm and decodes it into pcm.
function decode(b) { function decode(b) {
// Initialize Decoder with first 4 bytes of b. // Iterate over each chunk and decode it.
est = bytesToInt16(b[0], b[1]); let chunkLen;
idx = b[byteDepth]; var result = [];
step = stepTable[idx]; 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++) { result.push(...b.slice(off + chunkLenSize, off + chunkLenSize + byteDepth));
var twoNibs = b[i];
var nib2 = twoNibs >> 4;
var nib1 = (nib2 << 4) ^ twoNibs
var sample1 = int16ToBytes(decodeSample(nib1)) for (var i = off + headSize; i < off + chunkLen - b[off + chunkLenSize + 3]; i++) {
result.push(...sample1) var twoNibs = b[i];
var nib2 = twoNibs >> 4;
var nib1 = (nib2 << 4) ^ twoNibs;
var sample2 = int16ToBytes(decodeSample(nib2)) var sample1 = int16ToBytes(decodeSample(nib1));
result.push(...sample2) result.push(...sample1);
}
if (b[3] == 1) { var sample2 = int16ToBytes(decodeSample(nib2));
var padNib = b[b.length - 1] result.push(...sample2);
var sample = int16ToBytes(decodeSample(padNib)) }
result.push(...sample) if (b[off + chunkLenSize + 3] == 1) {
var padNib = b[off + chunkLen - 1];
var sample = int16ToBytes(decodeSample(padNib));
result.push(...sample);
}
} }
return result; return result;
} }
@ -124,5 +132,12 @@ function int16ToBytes(num) {
} }
function bytesToInt16(b) { 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));
} }