rtpvp9pay: add picture-id-offset property

Bring the VP9 payloader in sync in this regard to the VP8 payloader

Allowing setting the picture id to a known value is useful when testing.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4530>

subprojects/gst-plugins-good/docs/gst_plugins_cache.json

@@ -17031,6 +17031,20 @@
                         "readable": true,
                         "type": "GstVP9RTPPayMode",
                         "writable": true
+                    },
+                    "picture-id-offset": {
+                        "blurb": "Offset to add to the initial picture-id (-1 = random)",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "-1",
+                        "max": "32767",
+                        "min": "-1",
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "gint",
+                        "writable": true
                     }
                 },
                 "rank": "marginal"

subprojects/gst-plugins-good/gst/rtp/gstrtpvp9pay.c

@@ -41,11 +41,13 @@ GST_DEBUG_CATEGORY_STATIC (gst_rtp_vp9_pay_debug);
 #define GST_CAT_DEFAULT gst_rtp_vp9_pay_debug
 
 #define DEFAULT_PICTURE_ID_MODE VP9_PAY_NO_PICTURE_ID
+#define DEFAULT_PICTURE_ID_OFFSET (-1)
 
 enum
 {
   PROP_0,
-  PROP_PICTURE_ID_MODE
+  PROP_PICTURE_ID_MODE,
+  PROP_PICTURE_ID_OFFSET,
 };
 
 #define GST_TYPE_RTP_VP9_PAY_PICTURE_ID_MODE (gst_rtp_vp9_pay_picture_id_mode_get_type())
@@ -110,20 +112,29 @@ static void
 gst_rtp_vp9_pay_picture_id_reset (GstRtpVP9Pay * self)
 {
   gint nbits;
+  guint16 old_picture_id = self->picture_id;
 
   if (self->picture_id_mode == VP9_PAY_NO_PICTURE_ID) {
     self->picture_id = 0;
   } else {
-    self->picture_id = g_random_int ();
+    if (self->picture_id_offset == DEFAULT_PICTURE_ID_OFFSET) {
+      self->picture_id = g_random_int ();
+    } else {
+      self->picture_id = self->picture_id_offset;
+    }
     nbits = picture_id_field_len (self->picture_id_mode);
     self->picture_id &= (1 << nbits) - 1;
   }
+
+  GST_LOG_OBJECT (self, "picture-id reset %u -> %u",
+      old_picture_id, self->picture_id);
 }
 
 static void
 gst_rtp_vp9_pay_init (GstRtpVP9Pay * obj)
 {
   obj->picture_id_mode = DEFAULT_PICTURE_ID_MODE;
+  obj->picture_id_offset = DEFAULT_PICTURE_ID_OFFSET;
   gst_rtp_vp9_pay_picture_id_reset (obj);
 }
 
@@ -144,6 +155,19 @@ gst_rtp_vp9_pay_class_init (GstRtpVP9PayClass * gst_rtp_vp9_pay_class)
           GST_TYPE_RTP_VP9_PAY_PICTURE_ID_MODE, DEFAULT_PICTURE_ID_MODE,
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  /**
+   * rtpvp9pay:picture-id-offset:
+   *
+   * Offset to add to the initial picture-id (-1 = random)
+   *
+   * Since: 1.24
+   */
+  g_object_class_install_property (gobject_class, PROP_PICTURE_ID_OFFSET,
+      g_param_spec_int ("picture-id-offset", "Picture ID offset",
+          "Offset to add to the initial picture-id (-1 = random)",
+          -1, 0x7FFF, DEFAULT_PICTURE_ID_OFFSET,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   gst_element_class_add_static_pad_template (element_class,
       &gst_rtp_vp9_pay_sink_template);
   gst_element_class_add_static_pad_template (element_class,
@@ -174,6 +198,10 @@ gst_rtp_vp9_pay_set_property (GObject * object,
       rtpvp9pay->picture_id_mode = g_value_get_enum (value);
       gst_rtp_vp9_pay_picture_id_reset (rtpvp9pay);
       break;
+    case PROP_PICTURE_ID_OFFSET:
+      rtpvp9pay->picture_id_offset = g_value_get_int (value);
+      gst_rtp_vp9_pay_picture_id_reset (rtpvp9pay);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -190,6 +218,9 @@ gst_rtp_vp9_pay_get_property (GObject * object,
     case PROP_PICTURE_ID_MODE:
       g_value_set_enum (value, rtpvp9pay->picture_id_mode);
       break;
+    case PROP_PICTURE_ID_OFFSET:
+      g_value_set_int (value, rtpvp9pay->picture_id_offset);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;

subprojects/gst-plugins-good/gst/rtp/gstrtpvp9pay.h

@@ -60,6 +60,7 @@ struct _GstRtpVP9Pay
   guint width;
   guint height;
   GstVP9RtpPayPictureIDMode picture_id_mode;
+  gint picture_id_offset;
   guint16 picture_id;
 };