[AUDIO_WORKLET] clarify docs and use for renderSizeHint (#25760)

Minor clarification of the docs and example.

Author: cwoffenden

site/source/docs/api_reference/wasm_audio_worklets.rst

@@ -44,10 +44,11 @@ and then, these processors are instantiated one or more times in the audio
 processing graph as AudioWorkletNodes.
 
 Once a class type is instantiated on the Web Audio graph and the graph is
-running, a C/C++ function pointer callback will be invoked for each 128
-samples of the processed audio stream that flows through the node. Newer Web
-Audio API specs allow this to be changed, so for future compatibility use the
-``AudioSampleFrame``'s ``samplesPerChannel`` to get the value.
+running, a C/C++ function pointer callback will be invoked for each N samples
+of the processed audio stream that flows through the node (where N is is the
+number of samples per channel, exposed as ``AudioSampleFrame``'s
+``samplesPerChannel``, always 128 in the 1.0 Web Audio API, though with the 1.1
+API ``emscripten_create_audio_context()`` accepts a ``renderSizeHint`` option).
 
 This callback will be executed on a dedicated separate audio processing
 thread with real-time processing priority. Each Web Audio context will

system/include/emscripten/webaudio.h

@@ -102,7 +102,7 @@ typedef void (*EmscriptenWorkletProcessorCreatedCallback)(EMSCRIPTEN_WEBAUDIO_T
 void emscripten_create_wasm_audio_worklet_processor_async(EMSCRIPTEN_WEBAUDIO_T audioContext, const WebAudioWorkletProcessorCreateOptions *options, EmscriptenWorkletProcessorCreatedCallback callback, void *userData3);
 
 // Returns the number of samples processed per channel in an AudioSampleFrame, fixed at 128 in the Web Audio API 1.0 specification, and valid for the lifetime of the audio context.
-// For this to change from the default 128, the context would need to be created with a yet unexposed WebAudioWorkletProcessorCreateOptions renderSizeHint, part of the 1.1 Web Audio API.
+// For this to differ from the default 128, the context would need to be created with a WebAudioWorkletProcessorCreateOptions renderSizeHint, part of the 1.1 Web Audio API.
 int emscripten_audio_context_quantum_size(EMSCRIPTEN_WEBAUDIO_T audioContext);
 
 // Returns the sampling rate of the given Audio Context, e.g. 48000 or 44100 or similar.

test/webaudio/audioworklet_test_shared.inc

@@ -90,19 +90,24 @@ EmscriptenStartWebAudioWorkletCallback getStartCallback(void);
 
 // Common entry point for the mixer tests
 int main(void) {
-  char* const workletStack = memalign(16, AUDIO_STACK_SIZE);
-  emscripten_outf("Audio worklet stack at 0x%p", workletStack);
-  assert(workletStack);
-
-  // Set at least the latency hint to test the attribute setting
-  // (The render size we take from the calling code if set)
+  // Set at least the latency hint to test the attribute setting (the render
+  // size we take from the calling code if set).
   EmscriptenWebAudioCreateAttributes attrs = {
     .latencyHint = "balanced",
 #ifdef RENDER_SIZE_HINT
     .renderSizeHint = RENDER_SIZE_HINT
 #endif
   };
   EMSCRIPTEN_WEBAUDIO_T context = emscripten_create_audio_context(&attrs);
+  // With the 1.1 API this may be values other than 128
+  emscripten_outf("Audio context created with quantum size of %d samples", emscripten_audio_context_quantum_size(context));
+
+  // Here we create a fixed sized worklet stack, but could calculate taking the
+  // quantum size above (ins and outs * bytes per quantum).
+  char* const workletStack = memalign(16, AUDIO_STACK_SIZE);
+  emscripten_outf("Audio worklet stack at 0x%p", workletStack);
+  assert(workletStack);
+
   emscripten_start_wasm_audio_worklet_thread_async(context, workletStack, AUDIO_STACK_SIZE, getStartCallback(), NULL);
 
 #ifdef TEST_AND_EXIT