wasapi: Allow opening devices in exclusive mode
This provides much lower latency compared to opening in shared mode,
but it also means that the device cannot be opened by any other
application. The advantage is that the achievable latency is much
lower.
In shared mode, WASAPI's engine period is 10ms, and so that is the
lowest latency achievable.
In exclusive mode, the limit is the device period itself, which in my
testing with USB DACs, on-board PCI sound-cards, and HDMI cards is
between 2ms and 3.33ms.
We set our audioringbuffer limits to match the device, so the
achievable sink latency is 6-9ms. Further improvements can be made if
needed.
https://bugzilla.gnome.org/show_bug.cgi?id=793289
diff --git a/sys/wasapi/gstwasapiutil.c b/sys/wasapi/gstwasapiutil.c
index 1ad9ff6..9fcbd33 100644
--- a/sys/wasapi/gstwasapiutil.c
+++ b/sys/wasapi/gstwasapiutil.c
@@ -25,8 +25,6 @@
#include "gstwasapiutil.h"
#include "gstwasapidevice.h"
-#include <mmdeviceapi.h>
-
/* This was only added to MinGW in ~2015 and our Cerbero toolchain is too old */
#if defined(_MSC_VER)
#include <functiondiscoverykeys_devpkey.h>
@@ -428,9 +426,82 @@
}
gboolean
+gst_wasapi_util_get_device_format (GstElement * element,
+ gint device_mode, IMMDevice * device, IAudioClient * client,
+ WAVEFORMATEX ** ret_format)
+{
+ WAVEFORMATEX *format;
+ HRESULT hr;
+
+ *ret_format = NULL;
+
+ hr = IAudioClient_GetMixFormat (client, &format);
+ if (hr != S_OK || format == NULL) {
+ GST_ERROR_OBJECT (element, "GetMixFormat failed: %s",
+ gst_wasapi_util_hresult_to_string (hr));
+ return FALSE;
+ }
+
+ /* WASAPI always accepts the format returned by GetMixFormat in shared mode */
+ if (device_mode == AUDCLNT_SHAREMODE_SHARED)
+ goto out;
+
+ /* WASAPI may or may not support this format in exclusive mode */
+ hr = IAudioClient_IsFormatSupported (client, AUDCLNT_SHAREMODE_EXCLUSIVE,
+ format, NULL);
+ if (hr == S_OK)
+ goto out;
+
+ CoTaskMemFree (format);
+
+ /* Open the device property store, and get the format that WASAPI has been
+ * using for sending data to the device */
+ {
+ PROPVARIANT var;
+ IPropertyStore *prop_store = NULL;
+
+ hr = IMMDevice_OpenPropertyStore (device, STGM_READ, &prop_store);
+ if (hr != S_OK) {
+ GST_ERROR_OBJECT (element, "OpenPropertyStore failed: %s",
+ gst_wasapi_util_hresult_to_string (hr));
+ return FALSE;
+ }
+
+ hr = IPropertyStore_GetValue (prop_store, &PKEY_AudioEngine_DeviceFormat,
+ &var);
+ if (hr != S_OK) {
+ GST_ERROR_OBJECT (element, "GetValue failed: %s",
+ gst_wasapi_util_hresult_to_string (hr));
+ IUnknown_Release (prop_store);
+ return FALSE;
+ }
+
+ format = malloc (var.blob.cbSize);
+ memcpy (format, var.blob.pBlobData, var.blob.cbSize);
+
+ PropVariantClear (&var);
+ IUnknown_Release (prop_store);
+ }
+
+ /* WASAPI may or may not support this format in exclusive mode */
+ hr = IAudioClient_IsFormatSupported (client, AUDCLNT_SHAREMODE_EXCLUSIVE,
+ format, NULL);
+ if (hr == S_OK)
+ goto out;
+
+ GST_ERROR_OBJECT (element, "AudioEngine DeviceFormat not supported");
+ free (format);
+ return FALSE;
+
+out:
+ *ret_format = format;
+ return TRUE;
+}
+
+gboolean
gst_wasapi_util_get_device_client (GstElement * element,
gboolean capture, gint role, const wchar_t * device_strid,
- IAudioClient ** ret_client)
+ IMMDevice ** ret_device, IAudioClient ** ret_client)
{
gboolean res = FALSE;
HRESULT hr;
@@ -468,7 +539,9 @@
}
IUnknown_AddRef (client);
+ IUnknown_AddRef (device);
*ret_client = client;
+ *ret_device = device;
res = TRUE;
