WASAPI: Rework the data discontinuity recovery logic.

Public issue https://github.com/mackron/miniaudio/issues/572

miniaudio.h

@@ -22223,12 +22223,17 @@ static ma_result ma_device_read__wasapi(ma_device* pDevice, void* pFrames, ma_ui
         } else {
             /* We don't have any cached data pointer, so grab another one. */
             HRESULT hr;
-            DWORD flags;
+            DWORD flags = 0;
 
             /* First just ask WASAPI for a data buffer. If it's not available, we'll wait for more. */
             hr = ma_IAudioCaptureClient_GetBuffer((ma_IAudioCaptureClient*)pDevice->wasapi.pCaptureClient, (BYTE**)&pDevice->wasapi.pMappedBufferCapture, &pDevice->wasapi.mappedBufferCaptureCap, &flags, NULL, NULL);
             if (hr == S_OK) {
                 /* We got a data buffer. Continue to the next loop iteration which will then read from the mapped pointer. */
+                pDevice->wasapi.mappedBufferCaptureLen = pDevice->wasapi.mappedBufferCaptureCap;
+
+                if (flags != 0) {
+                    ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[WASAPI] Capture Flags: %ld\n", flags);
+                }
 
                 /* Overrun detection. */
                 if ((flags & MA_AUDCLNT_BUFFERFLAGS_DATA_DISCONTINUITY) != 0) {
@@ -22236,13 +22241,29 @@ static ma_result ma_device_read__wasapi(ma_device* pDevice, void* pFrames, ma_ui
                     ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[WASAPI] Data discontinuity (possible overrun). Attempting recovery. mappedBufferCaptureCap=%d\n", pDevice->wasapi.mappedBufferCaptureCap);
 
                     /*
-                    If we got an overrun it probably means we're straddling the end of the buffer. In order to prevent
-                    a never-ending sequence of glitches we're going to recover by completely clearing out the capture
-                    buffer.
+                    If we got an overrun it probably means we're straddling the end of the buffer. In normal capture
+                    mode this is the fault of the client application because they're responsible for ensuring data is
+                    processed fast enough. In duplex mode, however, the processing of audio is tied to the playback
+                    device, so this can possibly be the result of a timing de-sync.
+
+                    In capture mode we're not going to do any kind of recovery because the real fix is for the client
+                    application to process faster. In duplex mode, we'll treat this as a desync and reset the buffers
+                    to prevent a never-ending sequence of glitches due to straddling the end of the buffer.
                     */
-                    {
-                        ma_uint32 iterationCount = 4;   /* Safety to prevent an infinite loop. */
+                    if (pDevice->type == ma_device_type_duplex) {
+                        /*
+                        Experiment:
+
+                        If we empty out the *entire* buffer we may end up putting ourselves into an underrun position
+                        which isn't really any better than the overrun we're probably in right now. Instead we'll just
+                        empty out about half.
+                        */
                         ma_uint32 i;
+                        ma_uint32 periodCount = (pDevice->wasapi.actualBufferSizeInFramesCapture / pDevice->wasapi.periodSizeInFramesCapture);
+                        ma_uint32 iterationCount = periodCount / 2;
+                        if ((periodCount % 2) > 0) {
+                            iterationCount += 1;
+                        }
 
                         for (i = 0; i < iterationCount; i += 1) {
                             hr = ma_IAudioCaptureClient_ReleaseBuffer((ma_IAudioCaptureClient*)pDevice->wasapi.pCaptureClient, pDevice->wasapi.mappedBufferCaptureCap);
@@ -22251,11 +22272,26 @@ static ma_result ma_device_read__wasapi(ma_device* pDevice, void* pFrames, ma_ui
                                 break;
                             }
 
+                            flags = 0;
                             hr = ma_IAudioCaptureClient_GetBuffer((ma_IAudioCaptureClient*)pDevice->wasapi.pCaptureClient, (BYTE**)&pDevice->wasapi.pMappedBufferCapture, &pDevice->wasapi.mappedBufferCaptureCap, &flags, NULL, NULL);
                             if (hr == MA_AUDCLNT_S_BUFFER_EMPTY || FAILED(hr)) {
+                                /*
+                                The buffer has been completely emptied or an error occurred. In this case we'll need
+                                to reset the state of the mapped buffer which will trigger the next iteration to get
+                                a fresh buffer from WASAPI.
+                                */
+                                pDevice->wasapi.pMappedBufferCapture   = NULL;
+                                pDevice->wasapi.mappedBufferCaptureCap = 0;
+                                pDevice->wasapi.mappedBufferCaptureLen = 0;
+
                                 if (hr == MA_AUDCLNT_S_BUFFER_EMPTY) {
-                                    ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[WASAPI] Data discontinuity recovery: Buffer emptied.\n");
+                                    if ((flags & MA_AUDCLNT_BUFFERFLAGS_DATA_DISCONTINUITY) != 0) {
+                                        ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[WASAPI] Data discontinuity recovery: Buffer emptied, and data discontinuity still reported.\n");
+                                    } else {
+                                        ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[WASAPI] Data discontinuity recovery: Buffer emptied.\n");
+                                    }
                                 }
+
                                 if (FAILED(hr)) {
                                     ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[WASAPI] Data discontinuity recovery: IAudioCaptureClient_GetBuffer() failed with %d.\n", hr);
                                 }
@@ -22264,22 +22300,11 @@ static ma_result ma_device_read__wasapi(ma_device* pDevice, void* pFrames, ma_ui
                             }
                         }
 
-                        if (i == iterationCount) {
-                            ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[WASAPI] Data discontinuity recovery: Iteration limit reached.\n");
+                        /* If at this point we have a valid buffer mapped, make sure the buffer length is set appropriately. */
+                        if (pDevice->wasapi.pMappedBufferCapture != NULL) {
+                            pDevice->wasapi.mappedBufferCaptureLen = pDevice->wasapi.mappedBufferCaptureCap;
                         }
                     }
-
-                    /* We should not have a valid buffer at this point so make sure everything is empty. */
-                    pDevice->wasapi.pMappedBufferCapture   = NULL;
-                    pDevice->wasapi.mappedBufferCaptureCap = 0;
-                    pDevice->wasapi.mappedBufferCaptureLen = 0;
-                } else {
-                    /* The data is clean. */
-                    pDevice->wasapi.mappedBufferCaptureLen = pDevice->wasapi.mappedBufferCaptureCap;
-
-                    if (flags != 0) {
-                        ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[WASAPI] Capture Flags: %ld\n", flags);
-                    }
                 }
 
                 continue;