mirror of https://bitbucket.org/ausocean/av.git
72 lines
2.0 KiB
JavaScript
72 lines
2.0 KiB
JavaScript
|
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,
|
||
|
|
16, 17, 19, 21, 23, 25, 28, 31,
|
||
|
|
34, 37, 41, 45, 50, 55, 60, 66,
|
||
|
|
73, 80, 88, 97, 107, 118, 130, 143,
|
||
|
|
157, 173, 190, 209, 230, 253, 279, 307,
|
||
|
|
337, 371, 408, 449, 494, 544, 598, 658,
|
||
|
|
724, 796, 876, 963, 1060, 1166, 1282, 1411,
|
||
|
|
1552, 1707, 1878, 2066, 2272, 2499, 2749, 3024,
|
||
|
|
3327, 3660, 4026, 4428, 4871, 5358, 5894, 6484,
|
||
|
|
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.
|
||
|
|
|
||
|
|
let est, // Estimation of sample based on quantised ADPCM nibble.
|
||
|
|
idx, // Index to step used for estimation.
|
||
|
|
step;
|
||
|
|
|
||
|
|
function decode(b) {
|
||
|
|
// b should be a Uint8Array
|
||
|
|
if (!(b instanceof Uint8Array)) {
|
||
|
|
console.log("Error: data is not a Uint8Array");
|
||
|
|
return;
|
||
|
|
}
|
||
|
|
|
||
|
|
// Initialize Decoder with first 4 bytes of b.
|
||
|
|
est = (new Uint16Array(b.slice(0, 2).buffer))[1];
|
||
|
|
idx = b[byteDepth];
|
||
|
|
step = stepTable[idx];
|
||
|
|
|
||
|
|
var result = new Uint8Array(b.slice(0, 2));
|
||
|
|
|
||
|
|
for (var i = headBytes; i < b.length - b[3]; i++) {
|
||
|
|
var twoNibs = b[i];
|
||
|
|
var nib2 = twoNibs >> 4;
|
||
|
|
var nib1 = (nib2 << 4) ^ twoNibs
|
||
|
|
var firstBytes = decodeSample(nib1)
|
||
|
|
concat(result, firstBytes)
|
||
|
|
|
||
|
|
var secondBytes = decodeSample(nib2)
|
||
|
|
concat(result, secondBytes)
|
||
|
|
}
|
||
|
|
if (b[3] == 1) {
|
||
|
|
var padNib = b[b.length - 1]
|
||
|
|
var samp = decodeSample(padNib)
|
||
|
|
concat(result, samp)
|
||
|
|
}
|
||
|
|
|
||
|
|
return result;
|
||
|
|
}
|
||
|
|
|
||
|
|
// concat concatenates TypedArrays a and b of same type.
|
||
|
|
function concat(a, b) {
|
||
|
|
var c = new(a.constructor)(a.length + b.length);
|
||
|
|
c.set(a, 0);
|
||
|
|
c.set(b, a.length);
|
||
|
|
return c;
|
||
|
|
}
|