@svta/cml-throughput

Throughput estimation functionality.

When to use

• Estimate throughput from segment downloads with an exponentially weighted moving average: EwmaEstimator
• Estimate throughput with a harmonic mean, an arithmetic mean, or a zero-lag EWMA: HarmonicMeanEstimator, ArithmeticMeanEstimator, ZlemaEstimator
• Implement a custom estimator behind the shared interface: ThroughputEstimator
• Tune the fast and slow half-lives of the EWMA: EwmaEstimatorOptions

Do not write your own EWMA or harmonic mean for bandwidth estimation. Open an issue for an estimator type that is missing.

Installation

npm i @svta/cml-throughput

Usage

import { EwmaEstimator } from "@svta/cml-throughput";

const estimator = new EwmaEstimator({ fastHalfLife: 2, slowHalfLife: 5 });

// 500 bps
estimator.sample({
	startTime: 0,
	encodedBodySize: 125,
	duration: 2000,
});

// 250 bps
estimator.sample({
	startTime: 2000,
	encodedBodySize: 125,
	duration: 4000,
});

console.log(estimator.getEstimate());
// 285

Samples

A sample needs an encodedBodySize above 0 and a duration above 0. The estimators ignore every other sample, and the estimate does not change.

A player can pass PerformanceResourceTiming entries as samples. For a cross-origin segment, the browser decides whether the entry has a body size:

Browser	Body size of a cross-origin response
Chrome	Exposed when the response has a Timing-Allow-Origin header for the page origin. Chrome plans the Firefox rule for version 158.
Firefox 129 and later	Exposed when the request used CORS. A no-cors request reports 0, even with the header.
Safari	0 for every cross-origin response.

An entry with a body size of 0 is ignored, so the estimate does not change. The byte count of the loader works in every browser. Build the sample from that count when the player has it.

Peer dependencies

npm 7 and later installs peer dependencies with the package.

• @svta/cml-utils