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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 = [
-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));
}