@twilio/voice-sdk
Version:
Twilio's JavaScript Voice SDK
62 lines • 3.99 kB
JavaScript
const r0 = 94.768; // Constant used in computing "rFactor".
/**
* Calculate the mos score of a stats object
* @param {number} rtt
* @param {number} jitter
* @param {number} fractionLost - The fraction of packets that have been lost.
* Calculated by packetsLost / totalPackets
* @return {number | null} mos - Calculated MOS, `1.0` through roughly `4.5`.
* Returns `null` when any of the input parameters are not a `non-negative`
* number.
*/
export function calculate(rtt, jitter, fractionLost) {
if (typeof rtt !== 'number' ||
typeof jitter !== 'number' ||
typeof fractionLost !== 'number' ||
!isNonNegativeNumber(rtt) ||
!isNonNegativeNumber(jitter) ||
!isNonNegativeNumber(fractionLost)) {
return null;
}
// Compute the effective latency.
const effectiveLatency = rtt + (jitter * 2) + 10;
// Compute the initial "rFactor" from effective latency.
let rFactor = 0;
switch (true) {
case effectiveLatency < 160:
rFactor = r0 - (effectiveLatency / 40);
break;
case effectiveLatency < 1000:
rFactor = r0 - ((effectiveLatency - 120) / 10);
break;
}
// Adjust "rFactor" with the fraction of packets lost.
switch (true) {
case fractionLost <= (rFactor / 2.5):
rFactor = Math.max(rFactor - fractionLost * 2.5, 6.52);
break;
default:
rFactor = 0;
break;
}
// Compute MOS from "rFactor".
const mos = 1 +
(0.035 * rFactor) +
(0.000007 * rFactor) *
(rFactor - 60) *
(100 - rFactor);
return mos;
}
/**
* Returns true if and only if the parameter passed is a number, is not `NaN`,
* is finite, and is greater than or equal to `0`.
* @param n
*/
export function isNonNegativeNumber(n) {
return typeof n === 'number' && !isNaN(n) && isFinite(n) && n >= 0;
}
export default {
calculate,
isNonNegativeNumber,
};
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