OSS: Prime the playback buffer when starting the device.

miniaudio.h

@@ -39612,17 +39612,48 @@ static void ma_device_uninit__oss(ma_device* pDevice)
     ma_free(pDeviceStateOSS, ma_device_get_allocation_callbacks(pDevice));
 }
 
+
+static void ma_device_prime_playback_buffer__oss(ma_device* pDevice)
+{
+    ma_device_state_oss* pDeviceStateOSS = ma_device_get_backend_state__oss(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;
+            }
+    
+            write(pDeviceStateOSS->fdPlayback, buffer, framesToWriteThisIteration);
+            framesWritten += framesToWriteThisIteration;
+        }
+    }
+}
+
 /*
 Note on Starting and Stopping
 =============================
 In the past I was using SNDCTL_DSP_HALT to stop the device, however this results in issues when
 trying to resume the device again. If we use SNDCTL_DSP_HALT, the next write() or read() will
 fail. Instead what we need to do is just not write or read to and from the device when the
-device is not running.
+device is not running. As a result, the stop function for OSS is just an empty stub.
-
-As a result, both the start and stop functions for OSS are just empty stubs. The starting and
-stopping logic is handled by ma_device_write__oss() and ma_device_read__oss(). These will check
-the device state, and if the device is stopped they will simply not do any kind of processing.
 
 The downside to this technique is that I've noticed a fairly lengthy delay in stopping the
 device, up to a second. This is on a virtual machine, and as such might just be due to the
@@ -39630,13 +39661,22 @@ virtual drivers, but I'm not fully sure. I am not sure how to work around this p
 the moment that's just how it's going to have to be.
 
 When starting the device, OSS will automatically start it when write() or read() is called.
+
+UPDATE: 2026-01-14
+I'm no longer getting the stop delay when running from inside Virtual Box.
 */
 static ma_result ma_device_start__oss(ma_device* pDevice)
 {
-    MA_ASSERT(pDevice != NULL);
+    ma_device_type deviceType = ma_device_get_type(pDevice);
 
-    /* The device is automatically started with reading and writing. */
+    /*
-    (void)pDevice;
+    For playback we'll start the device by priming it with silence. Otherwise we'll do nothing
+    and let it start in step(). We want the playback buffer to be initially filled with silence
+    for the benefit of duplex mode.
+    */
+    if (deviceType == ma_device_type_playback || deviceType == ma_device_type_duplex) {
+        ma_device_prime_playback_buffer__oss(pDevice);
+    }
 
     return MA_SUCCESS;
 }