wasapi: Try to use latency-time and buffer-time

So far, we have been completely discarding the values of latency-time
and buffer-time and trying to always open the device in the lowest
latency mode possible. However, sometimes this is a bad idea:

1. When we want to save power/CPU and don't want low latency
2. When the lowest latency setting causes glitches
3. Other audio-driver bugs

Now we will try to follow the user-set values of latency-time and
buffer-time in shared mode, and only latency-time in exclusive mode (we
have no control over the hardware buffer size, and there is no use in
setting GstAudioRingBuffer size to something larger).

The elements will still try to open the devices in the lowest latency
mode possible if you set the "low-latency" property to "true".

https://bugzilla.gnome.org/show_bug.cgi?id=793289

6 files changed, 143 insertions, 53 deletions

diff --git a/sys/wasapi/gstwasapisink.c b/sys/wasapi/gstwasapisink.c
index 9fe393a06..81436cfa0 100644
--- a/sys/wasapi/gstwasapisink.c
+++ b/sys/wasapi/gstwasapisink.c
@@ -50,9 +50,10 @@ static GstStaticPadTemplate sink_template = GST_STATIC_PAD_TEMPLATE ("sink",
     GST_PAD_ALWAYS,
     GST_STATIC_CAPS (GST_WASAPI_STATIC_CAPS));
 
-#define DEFAULT_ROLE      GST_WASAPI_DEVICE_ROLE_CONSOLE
-#define DEFAULT_MUTE      FALSE
-#define DEFAULT_EXCLUSIVE FALSE
+#define DEFAULT_ROLE          GST_WASAPI_DEVICE_ROLE_CONSOLE
+#define DEFAULT_MUTE          FALSE
+#define DEFAULT_EXCLUSIVE     FALSE
+#define DEFAULT_LOW_LATENCY   FALSE
 
 enum
 {
@@ -60,7 +61,8 @@ enum
   PROP_ROLE,
   PROP_MUTE,
   PROP_DEVICE,
-  PROP_EXCLUSIVE
+  PROP_EXCLUSIVE,
+  PROP_LOW_LATENCY
 };
 
 static void gst_wasapi_sink_dispose (GObject * object);
@@ -124,6 +126,12 @@ gst_wasapi_sink_class_init (GstWasapiSinkClass * klass)
           "Open the device in exclusive mode",
           DEFAULT_EXCLUSIVE, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  g_object_class_install_property (gobject_class,
+      PROP_LOW_LATENCY,
+      g_param_spec_boolean ("low-latency", "Low latency",
+          "Optimize all settings for lowest latency",
+          DEFAULT_LOW_LATENCY, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   gst_element_class_add_static_pad_template (gstelement_class, &sink_template);
   gst_element_class_set_static_metadata (gstelement_class, "WasapiSrc",
       "Sink/Audio",
@@ -221,6 +229,9 @@ gst_wasapi_sink_set_property (GObject * object, guint prop_id,
       self->sharemode = g_value_get_boolean (value)
           ? AUDCLNT_SHAREMODE_EXCLUSIVE : AUDCLNT_SHAREMODE_SHARED;
       break;
+    case PROP_LOW_LATENCY:
+      self->low_latency = g_value_get_boolean (value);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -248,6 +259,9 @@ gst_wasapi_sink_get_property (GObject * object, guint prop_id,
       g_value_set_boolean (value,
           self->sharemode == AUDCLNT_SHAREMODE_EXCLUSIVE);
       break;
+    case PROP_LOW_LATENCY:
+      g_value_set_boolean (value, self->low_latency);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -376,42 +390,48 @@ gst_wasapi_sink_prepare (GstAudioSink * asink, GstAudioRingBufferSpec * spec)
   gboolean res = FALSE;
   REFERENCE_TIME latency_rt;
   IAudioRenderClient *render_client = NULL;
-  gint64 default_period, min_period, use_period;
+  REFERENCE_TIME default_period, min_period;
+  REFERENCE_TIME device_period, device_buffer_duration;
   guint bpf, rate;
   HRESULT hr;
 
-  hr = IAudioClient_GetDevicePeriod (self->client, &default_period, &min_period);
+  hr = IAudioClient_GetDevicePeriod (self->client, &default_period,
+      &min_period);
   if (hr != S_OK) {
     GST_ERROR_OBJECT (self, "IAudioClient::GetDevicePeriod failed");
-    goto beach;
+    return FALSE;
   }
+
   GST_INFO_OBJECT (self, "wasapi default period: %" G_GINT64_FORMAT
       ", min period: %" G_GINT64_FORMAT, default_period, min_period);
 
-  if (self->sharemode == AUDCLNT_SHAREMODE_SHARED) {
-    use_period = default_period;
-    /* Set hnsBufferDuration to 0, which should, in theory, tell the device to
-     * create a buffer with the smallest latency possible. In practice, this is
-     * usually 2 * default_period. See:
-     * https://msdn.microsoft.com/en-us/library/windows/desktop/dd370871(v=vs.85).aspx
-     *
-     * NOTE: min_period is a lie, and I have never seen WASAPI use it as the
-     * current period */
-    hr = IAudioClient_Initialize (self->client, AUDCLNT_SHAREMODE_SHARED,
-        AUDCLNT_STREAMFLAGS_EVENTCALLBACK, 0, 0, self->mix_format, NULL);
+  if (self->low_latency) {
+    if (self->sharemode == AUDCLNT_SHAREMODE_SHARED) {
+      device_period = default_period;
+      device_buffer_duration = 0;
+    } else {
+      device_period = min_period;
+      device_buffer_duration = min_period;
+    }
   } else {
-    use_period = min_period;
-    /* For some reason, we need to call this another time for exclusive mode */
-    CoInitialize (NULL);
-    /* FIXME: We should be able to use min_period as the device buffer size,
-     * but I'm hitting a problem in GStreamer. */
-    hr = IAudioClient_Initialize (self->client, AUDCLNT_SHAREMODE_EXCLUSIVE,
-        AUDCLNT_STREAMFLAGS_EVENTCALLBACK, use_period, use_period,
-        self->mix_format, NULL);
+    /* Clamp values to integral multiples of an appropriate period */
+    gst_wasapi_util_get_best_buffer_sizes (spec,
+        self->sharemode == AUDCLNT_SHAREMODE_EXCLUSIVE, default_period,
+        min_period, &device_period, &device_buffer_duration);
   }
+
+  /* For some reason, we need to call this a second time for exclusive mode */
+  if (self->sharemode == AUDCLNT_SHAREMODE_EXCLUSIVE)
+    CoInitialize (NULL);
+
+  hr = IAudioClient_Initialize (self->client, self->sharemode,
+      AUDCLNT_STREAMFLAGS_EVENTCALLBACK, device_buffer_duration,
+      /* This must always be 0 in shared mode */
+      self->sharemode == AUDCLNT_SHAREMODE_SHARED ? 0 : device_period,
+      self->mix_format, NULL);
   if (hr != S_OK) {
     gchar *msg = gst_wasapi_util_hresult_to_string (hr);
-    GST_ELEMENT_ERROR (self, RESOURCE, OPEN_READ, (NULL),
+    GST_ELEMENT_ERROR (self, RESOURCE, OPEN_WRITE, (NULL),
         ("IAudioClient::Initialize () failed: %s", msg));
     g_free (msg);
     goto beach;
@@ -431,7 +451,7 @@ gst_wasapi_sink_prepare (GstAudioSink * asink, GstAudioRingBufferSpec * spec)
 
   /* Actual latency-time/buffer-time are different now */
   spec->segsize = gst_util_uint64_scale_int_round (rate * bpf,
-      use_period * 100, GST_SECOND);
+      device_period * 100, GST_SECOND);
 
   /* We need a minimum of 2 segments to ensure glitch-free playback */
   spec->segtotal = MAX (self->buffer_frame_count * bpf / spec->segsize, 2);
diff --git a/sys/wasapi/gstwasapisink.h b/sys/wasapi/gstwasapisink.h
index 588d5807d..e445ce290 100644
--- a/sys/wasapi/gstwasapisink.h
+++ b/sys/wasapi/gstwasapisink.h
@@ -61,6 +61,7 @@ struct _GstWasapiSink
   gint role;
   gint sharemode;
   gboolean mute;
+  gboolean low_latency;
   wchar_t *device_strid;
 };
 
diff --git a/sys/wasapi/gstwasapisrc.c b/sys/wasapi/gstwasapisrc.c
index dcb196c86..375400914 100644
--- a/sys/wasapi/gstwasapisrc.c
+++ b/sys/wasapi/gstwasapisrc.c
@@ -48,15 +48,17 @@ static GstStaticPadTemplate src_template = GST_STATIC_PAD_TEMPLATE ("src",
     GST_PAD_ALWAYS,
     GST_STATIC_CAPS (GST_WASAPI_STATIC_CAPS));
 
-#define DEFAULT_ROLE      GST_WASAPI_DEVICE_ROLE_CONSOLE
-#define DEFAULT_EXCLUSIVE FALSE
+#define DEFAULT_ROLE          GST_WASAPI_DEVICE_ROLE_CONSOLE
+#define DEFAULT_EXCLUSIVE     FALSE
+#define DEFAULT_LOW_LATENCY   FALSE
 
 enum
 {
   PROP_0,
   PROP_ROLE,
   PROP_DEVICE,
-  PROP_EXCLUSIVE
+  PROP_EXCLUSIVE,
+  PROP_LOW_LATENCY
 };
 
 static void gst_wasapi_src_dispose (GObject * object);
@@ -116,6 +118,12 @@ gst_wasapi_src_class_init (GstWasapiSrcClass * klass)
           "Open the device in exclusive mode",
           DEFAULT_EXCLUSIVE, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  g_object_class_install_property (gobject_class,
+      PROP_LOW_LATENCY,
+      g_param_spec_boolean ("low-latency", "Low latency",
+          "Optimize all settings for lowest latency",
+          DEFAULT_LOW_LATENCY, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   gst_element_class_add_static_pad_template (gstelement_class, &src_template);
   gst_element_class_set_static_metadata (gstelement_class, "WasapiSrc",
       "Source/Audio",
@@ -218,6 +226,9 @@ gst_wasapi_src_set_property (GObject * object, guint prop_id,
       self->sharemode = g_value_get_boolean (value)
           ? AUDCLNT_SHAREMODE_EXCLUSIVE : AUDCLNT_SHAREMODE_SHARED;
       break;
+    case PROP_LOW_LATENCY:
+      self->low_latency = g_value_get_boolean (value);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -242,6 +253,9 @@ gst_wasapi_src_get_property (GObject * object, guint prop_id,
       g_value_set_boolean (value,
           self->sharemode == AUDCLNT_SHAREMODE_EXCLUSIVE);
       break;
+    case PROP_LOW_LATENCY:
+      g_value_set_boolean (value, self->low_latency);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -369,8 +383,8 @@ gst_wasapi_src_prepare (GstAudioSrc * asrc, GstAudioRingBufferSpec * spec)
   IAudioClock *client_clock = NULL;
   guint64 client_clock_freq = 0;
   IAudioCaptureClient *capture_client = NULL;
-  REFERENCE_TIME latency_rt;
-  gint64 default_period, min_period, use_period;
+  REFERENCE_TIME latency_rt, default_period, min_period;
+  REFERENCE_TIME device_period, device_buffer_duration;
   guint bpf, rate, buffer_frames;
   HRESULT hr;
 
@@ -383,27 +397,30 @@ gst_wasapi_src_prepare (GstAudioSrc * asrc, GstAudioRingBufferSpec * spec)
   GST_INFO_OBJECT (self, "wasapi default period: %" G_GINT64_FORMAT
       ", min period: %" G_GINT64_FORMAT, default_period, min_period);
 
-  if (self->sharemode == AUDCLNT_SHAREMODE_SHARED) {
-    use_period = default_period;
-    /* Set hnsBufferDuration to 0, which should, in theory, tell the device to
-     * create a buffer with the smallest latency possible. In practice, this is
-     * usually 2 * default_period. See:
-     * https://msdn.microsoft.com/en-us/library/windows/desktop/dd370871(v=vs.85).aspx
-     *
-     * NOTE: min_period is a lie, and I have never seen WASAPI use it as the
-     * current period */
-    hr = IAudioClient_Initialize (self->client, AUDCLNT_SHAREMODE_SHARED,
-        AUDCLNT_STREAMFLAGS_EVENTCALLBACK, 0, 0, self->mix_format, NULL);
+  if (self->low_latency) {
+    if (self->sharemode == AUDCLNT_SHAREMODE_SHARED) {
+      device_period = default_period;
+      device_buffer_duration = 0;
+    } else {
+      device_period = min_period;
+      device_buffer_duration = min_period;
+    }
   } else {
-    use_period = default_period;
-    /* For some reason, we need to call this another time for exclusive mode */
-    CoInitialize (NULL);
-    /* FIXME: We should be able to use min_period as the device buffer size,
-     * but I'm hitting a problem in GStreamer. */
-    hr = IAudioClient_Initialize (self->client, AUDCLNT_SHAREMODE_EXCLUSIVE,
-        AUDCLNT_STREAMFLAGS_EVENTCALLBACK, use_period, use_period,
-        self->mix_format, NULL);
+    /* Clamp values to integral multiples of an appropriate period */
+    gst_wasapi_util_get_best_buffer_sizes (spec,
+        self->sharemode == AUDCLNT_SHAREMODE_EXCLUSIVE, default_period,
+        min_period, &device_period, &device_buffer_duration);
   }
+
+  /* For some reason, we need to call this a second time for exclusive mode */
+  if (self->sharemode == AUDCLNT_SHAREMODE_EXCLUSIVE)
+    CoInitialize (NULL);
+
+  hr = IAudioClient_Initialize (self->client, self->sharemode,
+      AUDCLNT_STREAMFLAGS_EVENTCALLBACK, device_buffer_duration,
+      /* This must always be 0 in shared mode */
+      self->sharemode == AUDCLNT_SHAREMODE_SHARED ? 0 : device_period,
+      self->mix_format, NULL);
   if (hr != S_OK) {
     gchar *msg = gst_wasapi_util_hresult_to_string (hr);
     GST_ELEMENT_ERROR (self, RESOURCE, OPEN_READ, (NULL),
@@ -425,7 +442,7 @@ gst_wasapi_src_prepare (GstAudioSrc * asrc, GstAudioRingBufferSpec * spec)
       "rate is %i Hz", buffer_frames, bpf, rate);
 
   spec->segsize = gst_util_uint64_scale_int_round (rate * bpf,
-      use_period * 100, GST_SECOND);
+      device_period * 100, GST_SECOND);
 
   /* We need a minimum of 2 segments to ensure glitch-free playback */
   spec->segtotal = MAX (self->buffer_frame_count * bpf / spec->segsize, 2);
diff --git a/sys/wasapi/gstwasapisrc.h b/sys/wasapi/gstwasapisrc.h
index 530fb2b92..ca3f64146 100644
--- a/sys/wasapi/gstwasapisrc.h
+++ b/sys/wasapi/gstwasapisrc.h
@@ -62,6 +62,7 @@ struct _GstWasapiSrc
   /* properties */
   gint role;
   gint sharemode;
+  gboolean low_latency;
   wchar_t *device_strid;
 };
 
diff --git a/sys/wasapi/gstwasapiutil.c b/sys/wasapi/gstwasapiutil.c
index be25de558..402880aaf 100644
--- a/sys/wasapi/gstwasapiutil.c
+++ b/sys/wasapi/gstwasapiutil.c
@@ -814,3 +814,49 @@ gst_wasapi_util_parse_waveformatex (WAVEFORMATEXTENSIBLE * format,
 
   return TRUE;
 }
+
+void
+gst_wasapi_util_get_best_buffer_sizes (GstAudioRingBufferSpec * spec,
+    gboolean exclusive, REFERENCE_TIME default_period,
+    REFERENCE_TIME min_period, REFERENCE_TIME * ret_period,
+    REFERENCE_TIME * ret_buffer_duration)
+{
+  REFERENCE_TIME use_period, use_buffer;
+
+  /* Figure out what integral device period to use as the base */
+  if (exclusive) {
+    /* Exclusive mode can run at multiples of either the minimum period or the
+     * default period; these are on the hardware ringbuffer */
+    if (spec->latency_time * 10 > default_period)
+      use_period = default_period;
+    else
+      use_period = min_period;
+  } else {
+    /* Shared mode always runs at the default period, so if we want a larger
+     * period (for lower CPU usage), we do it as a multiple of that */
+    use_period = default_period;
+  }
+
+  /* Ensure that the period (latency_time) used is an integral multiple of
+   * either the default period or the minimum period */
+  use_period = use_period * MAX ((spec->latency_time * 10) / use_period, 1);
+
+  if (exclusive) {
+    /* Buffer duration is the same as the period in exclusive mode. The
+     * hardware is always writing out one buffer (of size *ret_period), and
+     * we're writing to the other one. */
+    use_buffer = use_period;
+  } else {
+    /* Ask WASAPI to create a software ringbuffer of at least this size; it may
+     * be larger so the actual buffer time may be different, which is why after
+     * initialization we read the buffer duration actually in-use and set
+     * segsize/segtotal from that. */
+    use_buffer = spec->buffer_time * 10;
+    /* Has to be at least twice the period */
+    if (use_buffer < 2 * use_period)
+      use_buffer = 2 * use_period;
+  }
+
+  *ret_period = use_period;
+  *ret_buffer_duration = use_buffer;
+}
diff --git a/sys/wasapi/gstwasapiutil.h b/sys/wasapi/gstwasapiutil.h
index 1584a649e..3ca96eceb 100644
--- a/sys/wasapi/gstwasapiutil.h
+++ b/sys/wasapi/gstwasapiutil.h
@@ -77,4 +77,9 @@ gboolean gst_wasapi_util_parse_waveformatex (WAVEFORMATEXTENSIBLE * format,
     GstCaps * template_caps, GstCaps ** out_caps,
     GstAudioChannelPosition ** out_positions);
 
+void gst_wasapi_util_get_best_buffer_sizes (GstAudioRingBufferSpec * spec,
+    gboolean exclusive, REFERENCE_TIME default_period,
+    REFERENCE_TIME min_period, REFERENCE_TIME * ret_period,
+    REFERENCE_TIME * ret_buffer_duration);
+
 #endif /* __GST_WASAPI_UTIL_H__ */