CTL reference

libopus is configured through opus_encoder_ctl / opus_decoder_ctl — a varargs interface keyed by integer request codes. libopus-wasm exposes this as encoderCtl(request, value) and decoderCtl(request, value), with the request codes published as the EncoderCtl and DecoderCtl enums.

Most tuning has a named setter; reach for CTLs when you need a request that has no dedicated helper.

#How it works

import { createEncoder, EncoderCtl } from "libopus-wasm";

const encoder = await createEncoder();
encoder.encoderCtl(EncoderCtl.SetBitrate, 32000);
encoder.getBitrate(); // 32000

import { createDecoder, DecoderCtl } from "libopus-wasm";

const decoder = await createDecoder();
decoder.decoderCtl(DecoderCtl.SetGain, 256); // +3 dB, Q8 fixed-point

#A curated, safe subset

encoderCtl and decoderCtl accept integer setter requests only. This is a deliberate safety boundary, not a thin wrapper over the C varargs API:

• Setters, not getters. Getter CTLs in libopus write through a pointer

argument. Passing a JS number where libopus expects an int* would corrupt WASM memory, so getters are exposed as explicit methods (getBitrate, getLookahead, getInDtx) instead.

• Allow-listed requests. Only the codes in EncoderCtl / DecoderCtl are

accepted. Any other request — including pointer-style ones — throws a RangeError at the JS boundary before touching WASM.

• Integers only. Both request and value must be integers, or the call

throws a RangeError.

encoder.encoderCtl(4003, 0); // RangeError: not an allow-listed integer setter

#Encoder requests

EncoderCtl contains the supported encoder setter codes:

// Tell Opus the input only carries 16 meaningful bits.
encoder.encoderCtl(EncoderCtl.SetLsbDepth, 16);

// Force a stereo encode even from a mono-leaning signal.
encoder.encoderCtl(EncoderCtl.SetForceChannels, 2);

#Decoder requests

DecoderCtl covers the supported decoder setters:

decoder.decoderCtl(DecoderCtl.SetGain, -256); // attenuate by 3 dB

#Next

• Encoder tuning — the named setters most code should use.
• API reference — enum values and method signatures.