See this addon for use of opus. https://store.godotengine.org/asset/joyless/opus-gdextension/

This addon will be changed to flac only.

Xiph Audio for Godot is a cross-platform Godot 4 GDExtension for loading and playing Ogg Opus (.opus) and FLAC (.flac) files as native AudioStream resources.

It supports duration reporting, seeking, simultaneous playback, and optional looping with a loop offset. Audio is decoded incrementally from compressed resource data. The addon loads automatically and does not require enabling an EditorPlugin.

The release includes debug and release binaries for Linux and Windows x86-64, universal macOS, iOS arm64, Android arm32/arm64/x86-32/x86-64, and threaded or single-threaded Web exports. Godot 4.5 or newer is required.

This addon provides decoding and playback only; it does not provide audio encoding or format conversion. Source, documentation, and issue tracking are available from the GitHub repository. A live WebAssembly demo is available on itch.io/godot-xiph-audio-demo.