audiolatency: Expose samplesperbuffer property

... for user to be able to set the number of required samples.
For instance, our default value is 240 samples
(about 5ms latency in case that sample rate is 48000), which might
be larger than actual buffer size of audio capture device.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2307>

docs/plugins/gst_plugins_cache.json

@@ -1261,6 +1261,20 @@
                         "readable": true,
                         "type": "gboolean",
                         "writable": true
+                    },
+                    "samplesperbuffer": {
+                        "blurb": "Number of samples in each outgoing buffer",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "240",
+                        "max": "2147483647",
+                        "min": "1",
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "gint",
+                        "writable": true
                     }
                 },
                 "rank": "primary"

gst/audiolatency/gstaudiolatency.c

@@ -86,12 +86,15 @@ GST_ELEMENT_REGISTER_DEFINE (audiolatency, "audiolatency", GST_RANK_PRIMARY,
     GST_TYPE_AUDIOLATENCY);
 
 #define DEFAULT_PRINT_LATENCY   FALSE
+#define DEFAULT_SAMPLES_PER_BUFFER 240
+
 enum
 {
   PROP_0,
   PROP_PRINT_LATENCY,
   PROP_LAST_LATENCY,
-  PROP_AVERAGE_LATENCY
+  PROP_AVERAGE_LATENCY,
+  PROP_SAMPLES_PER_BUFFER,
 };
 
 static gint64 gst_audiolatency_get_latency (GstAudioLatency * self);
@@ -119,6 +122,9 @@ gst_audiolatency_get_property (GObject * object,
     case PROP_AVERAGE_LATENCY:
       g_value_set_int64 (value, gst_audiolatency_get_average_latency (self));
       break;
+    case PROP_SAMPLES_PER_BUFFER:
+      g_value_set_int (value, self->samples_per_buffer);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -135,6 +141,11 @@ gst_audiolatency_set_property (GObject * object,
     case PROP_PRINT_LATENCY:
       self->print_latency = g_value_get_boolean (value);
       break;
+    case PROP_SAMPLES_PER_BUFFER:
+      self->samples_per_buffer = g_value_get_int (value);
+      g_object_set (self->audiosrc,
+          "samplesperbuffer", self->samples_per_buffer, NULL);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -165,6 +176,20 @@ gst_audiolatency_class_init (GstAudioLatencyClass * klass)
           "The running average latency, in microseconds", 0,
           G_USEC_PER_SEC, 0, G_PARAM_READABLE | G_PARAM_STATIC_STRINGS));
 
+  /**
+   * GstAudioLatency:samplesperbuffer:
+   *
+   * The number of audio samples in each outgoing buffer.
+   * See also #GstAudioTestSrc:samplesperbuffer
+   *
+   * Since: 1.20
+   */
+  g_object_class_install_property (gobject_class, PROP_SAMPLES_PER_BUFFER,
+      g_param_spec_int ("samplesperbuffer", "Samples per buffer",
+          "Number of samples in each outgoing buffer",
+          1, G_MAXINT, DEFAULT_SAMPLES_PER_BUFFER,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   gst_element_class_add_static_pad_template (gstelement_class, &src_template);
   gst_element_class_add_static_pad_template (gstelement_class, &sink_template);
 
@@ -183,6 +208,7 @@ gst_audiolatency_init (GstAudioLatency * self)
   self->send_pts = 0;
   self->recv_pts = 0;
   self->print_latency = DEFAULT_PRINT_LATENCY;
+  self->samples_per_buffer = DEFAULT_SAMPLES_PER_BUFFER;
 
   /* Setup sinkpad */
   self->sinkpad = gst_pad_new_from_static_template (&sink_template, "sink");
@@ -195,8 +221,8 @@ gst_audiolatency_init (GstAudioLatency * self)
 
   /* Setup srcpad */
   self->audiosrc = gst_element_factory_make ("audiotestsrc", NULL);
-  g_object_set (self->audiosrc, "wave", 8, "samplesperbuffer", 240,
-      "is-live", TRUE, NULL);
+  g_object_set (self->audiosrc, "wave", 8, "samplesperbuffer",
+      DEFAULT_SAMPLES_PER_BUFFER, "is-live", TRUE, NULL);
   gst_bin_add (GST_BIN (self), self->audiosrc);
 
   templ = gst_static_pad_template_get (&src_template);

gst/audiolatency/gstaudiolatency.h

@@ -56,6 +56,7 @@ struct _GstAudioLatency
 
   /* properties */
   gboolean print_latency;
+  gint samples_per_buffer;
 };
 
 struct _GstAudioLatencyClass