Emscripten WebAssembly Audio Worklets example

audio.cpp

#include <emscripten/webaudio.h>
#include <emscripten/em_math.h>
float phase = 0.f;
EM_BOOL ProcessAudio(int numInputs, const AudioSampleFrame *inputs,
                     int numOutputs, AudioSampleFrame *outputs,
                     int numParams, const AudioParamFrame *params, void *userData) {
  for(int i = 0; i < 128; ++i) {
    outputs[0].data[i] = emscripten_math_sin(phase);
    phase = emscripten_math_fmod(phase + 0.05f, 2.f * EM_MATH_PI);
  }
  return EM_TRUE;
}
char stack[4096];
int main() {
  EMSCRIPTEN_WEBAUDIO_T context = emscripten_create_audio_context(0);
  emscripten_start_wasm_audio_worklet_thread_async(context, stack, sizeof(stack), [](EMSCRIPTEN_WEBAUDIO_T context, EM_BOOL success, void *userData) {
    WebAudioWorkletProcessorCreateOptions opts = { .name = "my-processor-class" };
    emscripten_create_wasm_audio_worklet_processor_async(context, &opts, [](EMSCRIPTEN_WEBAUDIO_T context, EM_BOOL success, void *userData){
      int outputChannelCounts[1] = { 1 };
      EmscriptenAudioWorkletNodeCreateOptions options = {
        .numberOfInputs = 0,
        .numberOfOutputs = 1,
        .outputChannelCounts = outputChannelCounts
      };
      EMSCRIPTEN_AUDIO_WORKLET_NODE_T workletNode = emscripten_create_wasm_audio_worklet_node(context, "my-processor-class", &options, &ProcessAudio, 0);
      EM_ASM({
        let context = emscriptenGetAudioObject($0);
        let workletNode = emscriptenGetAudioObject($1);
        workletNode.connect(context.destination);
        let button = document.body.appendChild(document.createElement('button'));
        button.innerHTML = 'Start';
        button.onclick = () => { context.resume(); };
      }, context, workletNode);
     }, 0);
  }, 0);
}