sndio: Prime the playback buffer when starting the device.

miniaudio.h

@@ -37606,6 +37606,41 @@ static void ma_device_uninit__sndio(ma_device* pDevice)
     ma_free(pDeviceStateSndio, ma_device_get_allocation_callbacks(pDevice));
 }
 
+static void ma_device_prime_playback_buffer__sndio(ma_device* pDevice)
+{
+    ma_device_state_sndio* pDeviceStateSndio = ma_device_get_backend_state__sndio(pDevice);
+    ma_context_state_sndio* pContextStateSndio = ma_context_get_backend_state__sndio(ma_device_get_context(pDevice));
+    ma_device_type deviceType = ma_device_get_type(pDevice);
+    ma_uint8 buffer[4096];
+    ma_uint32 bpf;
+    ma_uint32 framesToWrite;
+    ma_uint32 framesWritten;
+
+    if (deviceType == ma_device_type_playback || deviceType == ma_device_type_duplex) {
+        bpf = ma_get_bytes_per_frame(pDevice->playback.internalFormat, pDevice->playback.internalChannels);
+        framesToWrite = pDevice->playback.internalPeriodSizeInFrames * pDevice->playback.internalPeriods;
+        framesWritten = 0;
+    
+        MA_ZERO_MEMORY(buffer, sizeof(buffer));
+    
+        while (framesWritten < framesToWrite) {
+            ma_uint32 framesToWriteThisIteration = sizeof(buffer) / bpf;
+            ma_uint32 framesRemaining = framesToWrite - framesWritten;
+            if (framesToWriteThisIteration > framesRemaining) {
+                framesToWriteThisIteration = framesRemaining;
+            }
+    
+            /* Just a guard to ensure we don't get stuck in a loop. Should never happen in practice (would require a massive channel count). */
+            if (framesToWriteThisIteration == 0) {
+                break;
+            }
+    
+            pContextStateSndio->sio_write(pDeviceStateSndio->playback.handle, buffer, framesToWriteThisIteration * bpf);
+            framesWritten += framesToWriteThisIteration;
+        }
+    }
+}
+
 static ma_result ma_device_start__sndio(ma_device* pDevice)
 {
     ma_device_state_sndio* pDeviceStateSndio = ma_device_get_backend_state__sndio(pDevice);
@@ -37618,6 +37653,12 @@ static ma_result ma_device_start__sndio(ma_device* pDevice)
 
     if (deviceType == ma_device_type_playback || deviceType == ma_device_type_duplex) {
         pContextStateSndio->sio_start(pDeviceStateSndio->playback.handle);   /* <-- Doesn't actually start until data is written. */
+
+        /*
+        Prime the playback buffer with silence. This mainly for duplex mode which needs
+        a buffer of silence to give the capture side time to produce audio.
+        */
+        ma_device_prime_playback_buffer__sndio(pDevice);
     }
 
     return MA_SUCCESS;