CODEWITHSUNDEEP
javascriptweb-audio-apityped-arrays
Wilson Luniz
Wilson Luniz

Reputation: 479

Javascript: UInt8Array to Float32Array

I have some audio buffer in usigned 8bit PCM format need to play via web audio which only accept signed 32bit PCM. And now I have ArrayBuffer for pieces of pcm_u8 data(come from Uint8array). How can I convert it to Float32Array?

Upvotes: 8

Views: 12586

Answers (3)

Jaromanda X
Jaromanda X

Reputation: 1

This function converts an ArrayBuffer to Float32Array

function convertBlock(buffer) { // incoming data is an ArrayBuffer
    var incomingData = new Uint8Array(buffer); // create a uint8 view on the ArrayBuffer
    var i, l = incomingData.length; // length, we need this for the loop
    var outputData = new Float32Array(incomingData.length); // create the Float32Array for output
    for (i = 0; i < l; i++) {
        outputData[i] = (incomingData[i] - 128) / 128.0; // convert audio to float
    }
    return outputData; // return the Float32Array
}

This one converts a Uint8Array to Float32Array

function convertBlock(incomingData) { // incoming data is a UInt8Array
    var i, l = incomingData.length;
    var outputData = new Float32Array(incomingData.length);
    for (i = 0; i < l; i++) {
        outputData[i] = (incomingData[i] - 128) / 128.0;
    }
    return outputData;
}

Note: A few months after writing this answer, Safari finally caught up and made the TypedArray.from method available (as noted in another answer)

So, the code would be simply (for an ArrayBuffer input)

const convertBlock = input => Float32Array.from(new Uint8Array(input), v => (v - 128) / 128);

For Uint8Array input, you could still use the above, or simpler:

const convertBlock = input => Float32Array.from(input, v => (v - 128) / 128);

Upvotes: 14

Mahmoud
Mahmoud

Reputation: 11441

grab Uint8Array's underlying ArrayBuffer and pass it to the Float32Array constructor:

const f_sz = 42; // length of elements in f
const a = new Uint8Array();
const b = a.buffer; // ArrayBuffer
const f = new Float32Array(b, 0, f_sz);

may also work:

const b = a.buffer; // ArrayBuffer
const f = new Float32Array(b);

ref: Float32Array() constructor

Upvotes: 0

robjtede
robjtede

Reputation: 746

ECMAScript 2015 and onwards has TypedArray.from which converts any typed array (and indeed, any iterable) to the specified typed array format.

So converting a Uint8Array to a Float32Array is now as easy as:

const intArray = new Uint8Array()
const floatArray = Float32Array.from(intArray)

Upvotes: 16

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