feat: logarithmic volume support

[christriants]

Description

Addresses: #8498

This PR adds support for logarithmic (perceptual) volume control to Video.js, providing a more natural audio experience that better matches human perception of loudness. When enabled via the logarithmicVolume option, the volume slider uses decibel-based scaling where linear slider movements produce logarithmic volume changes, making volume adjustments feel more consistent across the entire range.

The Problem:

As discussed in issue #8498, traditional linear volume control doesn't match how humans perceive sound. With linear scaling:

• Moving from 10% to 20% can feel like a huge jump in loudness
• Moving from 80% to 90% is barely noticeable
• Fine control at low volumes is difficult, making it hard to find a comfortable quiet listening level

Specific Changes proposed

Logarithmic volume control solves this by using decibel (dB) scaling, the audio engineering standard that matches human hearing perception (source). This implementation provides finer control at lower volumes where precision matters most - the first 50% of the slider covers roughly 0-6% of actual volume. This solution remains fully backward compatible - linear volume remains the default behavior.

Usage:

const player = videojs('my-video', {
  logarithmicVolume: true,
  logarithmicVolumeRange: 50
});

New VolumeTransfer class:

• src/js/utils/volume-transfer.js - Volume transfer functions for converting between slider position and player volume
• includes VolumeTransfer (base class), LinearVolumeTransfer (default, maintains current behavior), and LogarithmicVolumeTransfer (decibel-based scaling)

Updates to VolumeBar:

• src/js/controls/volume-control/volume-bar.js
• Added initVolumeTransfer_() to initialize transfer function based on logarithmicVolume option
• Updated handleMouseMove(), getPercent(), stepForward(), and stepBack() to use transfer functions

New Player Options:

• Added logarithmicVolume option (boolean, default: false)
  Added logarithmicVolumeRange option (number, default: 50)

Tests:
test/unit/utils/volume-transfer.test.js - Test suite covering both transfer implementations

Test Page:
https://christriants.github.io/video.js/sandbox/logarithmic-volume.html

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chrome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
  • Has no DOM changes which impact accessiblilty or trigger warnings (e.g. Chrome issues tab)
  • Has no changes to JSDoc which cause npm run docs:api to error
• Reviewed by Two Core Contributors

[welcome]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.65%. Comparing base (d203eab) to head (2def34d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9124      +/-   ##
==========================================
+ Coverage   84.31%   84.65%   +0.34%     
==========================================
  Files         120      121       +1     
  Lines        8154     8199      +45     
  Branches     1964     1971       +7     
==========================================
+ Hits         6875     6941      +66     
+ Misses       1279     1258      -21     

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[mister-ben]

Suggested change

	QUnit.test.only('VolumeBar stepBack() sets volume to 0 when slider would go below threshold', function(assert) {
	QUnit.test('VolumeBar stepBack() sets volume to 0 when slider would go below threshold', function(assert) {

Coverage ought to pass without the only left in.

[christriants]

Thanks, @mister-ben. Updated.