Bug 311451 – Degraded audio quality with microphone enabled

• Status: NEW
• Component: WebRTC

Overview

After activating the microphone via navigator.mediaDevices.getUserMedia(), output audio quality is degraded.

getUserMedia API: https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/getUserMedia

Steps to Reproduce

1. Begin audio playback (a WebRTC stream or more directly an HTML audio element have been tested)
2. Begin microphone capture with navigator.mediaDevices.getUserMedia(). You may capture without constraints with navigator.mediaDevices.getUserMedia({audio: true, video: false}), or include constraints such as navigator.mediaDevices.getUserMedia({audio: {echoCancellation: false}, video: false}). My understanding is that echo cancellation is currently the only constraint used by Safari.

Actual Results

With or without the echoCancellation: false constraint, audio quality after step 2 is degraded in terms of:

1. Reduced sample rate
2. Stereo audio converted to mono

These are more noticeable with a high quality audio file or with music. The degradation may be more apparent depending on the audio output device, especially headphones. 

Expected Results

With the {echoCancellation: false} constraint (or possibly additional constraints if they become supported), audio quality should ideally remain roughly the same as without microphone capture active. This supports the case of applications and games that may capture the microphone but not require the audio processing of a call.

Build Date and Hardware

Appears to be a longstanding issue in Safari on iOS and iPadOS, most recently affecting iOS 26.4 on iPhone 15 pro.

Additional Builds and Platforms

Does not affect Safari on MacOS.

Additional Information

This is a separate issue from https://bugs.webkit.org/show_bug.cgi?id=218012, which focused on possible changes in audio volume when beginning microphone capture.

[Radar WebKit Bug Importer]

<rdar://problem/174529097>

Created attachment 479097 [details]
Demo with WebRTC, serve with HTTPS for mic access on iOS

I attached a demo HTML file for the issue. It is also hosted here: https://webrtc.nvidia.com/api-tests/mic-audio/webrtc/josh-test.html. This is a version of the demo which does not use an additional audio file, but it is harder to hear the difference in quality: https://webrtc.nvidia.com/api-tests/mic-audio/webrtc/ashish-test.html.

To add some context on replicating this issue in production GeForce Now:

- Launch play.geforcenow.com as a PWA on iPhone (free subscription tier is okay)
- Enter a game, Genshin Impact is an example of a free game where this issue is noticeable
- When launching the game you should enter a login screen with background music playing
- In GeForce Now the microphone can be enabled during a stream by pressing the microphone icon in the top left
- After enabling the microphone the audio quality is degraded for the remainder of the session (resets after exiting game)
- The degree of perceivable audio quality degradation depends on the device, but on AirPods the Genshin Impact background music becomes tinny and has some static/crackle
- The degradation is still audible on iPhone device speakers, but seems to be more pronounced on higher quality output devices 

Going through these steps should demonstrate the loss of quality for GFN users playing with the microphone enabled.

[Byungseon(Sun) Shin]

Created attachment 480598 [details]
iOS-macOS 27 public beta test report

Attached iOS-macOS 27 public beta test report. The reported issue still persist on the latest iOS & macOS 27 public beta.