audio: Let emscripten update device->sample_frames at device open time.

Fixes #11435.

src/audio/SDL_audio.c

@@ -144,7 +144,7 @@ const char *SDL_GetCurrentAudioDriver(void)
     return current_audio.name;
 }
 
-static int GetDefaultSampleFramesFromFreq(const int freq)
+int SDL_GetDefaultSampleFramesFromFreq(const int freq)
 {
     const char *hint = SDL_GetHint(SDL_HINT_AUDIO_DEVICE_SAMPLE_FRAMES);
     if (hint) {
@@ -626,7 +626,7 @@ static SDL_AudioDevice *CreatePhysicalAudioDevice(const char *name, bool recordi
     device->recording = recording;
     SDL_copyp(&device->spec, spec);
     SDL_copyp(&device->default_spec, spec);
-    device->sample_frames = GetDefaultSampleFramesFromFreq(device->spec.freq);
+    device->sample_frames = SDL_GetDefaultSampleFramesFromFreq(device->spec.freq);
     device->silence_value = SDL_GetSilenceValueForFormat(device->spec.format);
     device->handle = handle;
 
@@ -1666,7 +1666,7 @@ static bool OpenPhysicalAudioDevice(SDL_AudioDevice *device, const SDL_AudioSpec
     device->spec.format = (SDL_AUDIO_BITSIZE(device->default_spec.format) >= SDL_AUDIO_BITSIZE(spec.format)) ? device->default_spec.format : spec.format;
     device->spec.freq = SDL_max(device->default_spec.freq, spec.freq);
     device->spec.channels = SDL_max(device->default_spec.channels, spec.channels);
-    device->sample_frames = GetDefaultSampleFramesFromFreq(device->spec.freq);
+    device->sample_frames = SDL_GetDefaultSampleFramesFromFreq(device->spec.freq);
     SDL_UpdatedAudioDeviceFormat(device);  // start this off sane.
 
     device->currently_opened = true;  // mark this true even if impl.OpenDevice fails, so we know to clean up.

src/audio/SDL_sysaudio.h

@@ -91,6 +91,9 @@ extern SDL_AudioDevice *SDL_FindPhysicalAudioDeviceByCallback(bool (*callback)(S
 // Backends should call this if they change the device format, channels, freq, or sample_frames to keep other state correct.
 extern void SDL_UpdatedAudioDeviceFormat(SDL_AudioDevice *device);
 
+// Backends can call this to get a reasonable default sample frame count for a device's sample rate.
+int SDL_GetDefaultSampleFramesFromFreq(const int freq);
+
 // Backends can call this to get a standardized name for a thread to power a specific audio device.
 extern char *SDL_GetAudioThreadName(SDL_AudioDevice *device, char *buf, size_t buflen);
 

src/audio/emscripten/SDL_emscriptenaudio.c

@@ -190,6 +190,7 @@ static bool EMSCRIPTENAUDIO_OpenDevice(SDL_AudioDevice *device)
 
     // limit to native freq
     device->spec.freq = EM_ASM_INT({ return Module['SDL3'].audioContext.sampleRate; });
+    device->sample_frames = SDL_GetDefaultSampleFramesFromFreq(device->spec.freq);
 
     SDL_UpdatedAudioDeviceFormat(device);