Garbled audio with AudioStreamSynchronized on no-threads web builds

[elliotfontaine]

Tested versions

• v4.3.stable.official [77dcf97d8],
• v4.4.1.stable.official [49a5bc7b6],
• v4.5.beta5.official [c81fd6c51].

System information

MacOS 12.7.4 - OpenGL3 (gl_compatibility) - Intel Iris Pro OpenGL Engine (Intel Inc.) - Intel(R) Core(TM) i7-4750HQ CPU @ 2.00GHz (8 Threads) - Brave Browser

Issue description

This is a follow-up to #87329, which was marked as fixed. The fix from #91382 appears to resolve audio crackling for most AudioStream resources, but AudioStreamSynchronized is still affected on no-threads Web builds.

This may also affect other AudioStream subclasses, but testing was limited to AudioStreamSynchronized and AudioStreamMP3 (the latter working as expected).

This might be the root cause of some previous reports, namely:

• Audio cracks with lower end devices on web builds - no threads. #103442

Steps to reproduce

Run elliotfontaine/godot-web-audio-garble (ZIP archive available below) in the browser. Third demo on the right, AudioStreamSynchronized (3), should produce garbled audio.

Minimal reproduction project (MRP)

web-audio-garble.zip