Conversion Error : ArrayBuffer to Int16Array

Question

this should be straight forward, but I am not sure why I am getting the error, I am using constructor with ArrayBuffer as parameter as shown in mdn, but I am getting the error as invalid arguments, (p.s with dataview I have checked, the data is Int16 only)

the code is:

        var view= DataView(arrayBuf);
        console.log('arrayBuf.byteLength : '+arrayBuf.byteLength);
        console.log('data at 0 : '+view.getInt16(0));
        console.log('data at 1 : '+view.getInt16(1));
        var int16arry = new Int16Array(arrayBuf);

the console output is:

"arrayBuf.byteLength : 117" 
"data at 0 : 22720" 
"data at 1 : -16315"
Error: invalid arguments

what is my mistake?

Hmm, an array of 16 bit ints should always have an even number of bytes. If you try to calculate how many int16 you have in your arrayBuffer you end up with 58,5 ints, and that wont work. What else have you padded in there? If you do in fact have different data types that i have a script for you if you want it — Snellface
– Snellface, Commented Sep 30, 2014 at 7:35
@Snellface unfortunately these arraybuffers are what I recieve from a library which has no documentation, these are encoded packets, and they work fine when I individually copy them using DataView, also i do not understand how, length of packet/Int16Array is 117 and not 117/2, that y i am increasing view.getInt16(0), as 0,1,2, and not `,2,4... — mido
– mido, Commented Sep 30, 2014 at 7:45
arrayBuf.byteLength gives you the number of bytes in the buffer regardless of their type. So your buffer is either not received correctly, or it contains something other then "only" 16bit integers. If you loop through them one by one and extract them with getInt16, can you make sure that the data you are getting is actually what you are expecting to get? After you have read the final "full" int16, try reading an int8 and see what you get? — Snellface
– Snellface, Commented Sep 30, 2014 at 7:53
Ps, you could try this: var int16arry = new Int16Array(arrayBuf, 0, Math.floor(arrayBuf.byteLength / 2)); This will remove the last "half" 16bit int in the end, but i would call that a hack since you do not know why there is an extra byte, and what it is used for :P You can read this in the documentation you linked, but the function i used here take these arguments: Int16Array(buffer, start index, number of entries to read); — Snellface
– Snellface, Commented Sep 30, 2014 at 7:55
Btw, what library are you using? Or more specifically what language is it written in? (If you are using a javascript library you can probably look at the source code of the function which gives you your array buffer, and that might give you a clue as to why you are receiving an extra byte) — Snellface
– Snellface, Commented Sep 30, 2014 at 8:10

Snellface · Accepted Answer · 2014-09-30 09:04:22Z

2

The short answer is that your arrayBuffer is in the wrong size. You can use:

var int16Array = new Int16Array(arrayBuf, 0, Math.floor(arrayBuf.byteLength / 2));

to hack away the problem.

Case specific comment:
I have tried reading the source for your library but i am unable to see why you are getting that extra byte (or what is missing).
The data you are getting is supposed to be 16 bit ints but for some reason you have other data there that take up an uneven amount of bytes, and according to the source as far as i can tell there should be some doubles (javascript floats) in there as well, meaning that "hacking" away the problem might not work.

answered Sep 30, 2014 at 9:04

Snellface

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2 Comments

mido Over a year ago

I found the solution to the problem, used UInt8Array, it would take care of the odd/even problem, thx for the time spent on this.

Snellface Over a year ago

Do you still get the correct values? The name of the function you told me that you use implies that it will use 16bit ints ("_i16" at the end of the name) Great if it works anyways!

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