rtpvp8pay: Add picture-id-offset property

Add property to set the initial value for picture-id. RFC7741 says
that picture-id MAY be initialized to a random value, thus it's also
valid to simply set it to a fixed initial value. A fixed value is very
useful for testing.

Default behavior is not changed.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/728>

docs/gst_plugins_cache.json

@@ -15764,6 +15764,20 @@
                         "readable": true,
                         "type": "GstVP8RTPPayMode",
                         "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"

gst/rtp/gstrtpvp8pay.c

@@ -39,11 +39,13 @@ GST_DEBUG_CATEGORY_STATIC (gst_rtp_vp8_pay_debug);
 #define GST_CAT_DEFAULT gst_rtp_vp8_pay_debug
 
 #define DEFAULT_PICTURE_ID_MODE VP8_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_VP8_PAY_PICTURE_ID_MODE (gst_rtp_vp8_pay_picture_id_mode_get_type())
@@ -93,7 +95,7 @@ GST_STATIC_PAD_TEMPLATE ("sink",
     GST_STATIC_CAPS ("video/x-vp8"));
 
 static gint
-picture_id_bitsize_from_mode (PictureIDMode mode)
+picture_id_field_len (PictureIDMode mode)
 {
   if (VP8_PAY_NO_PICTURE_ID == mode)
     return 0;
@@ -105,20 +107,28 @@ picture_id_bitsize_from_mode (PictureIDMode mode)
 static void
 gst_rtp_vp8_pay_picture_id_reset (GstRtpVP8Pay * obj)
 {
-  gint picture_id_bitsize = picture_id_bitsize_from_mode (obj->picture_id_mode);
-  if (0 == picture_id_bitsize)
-      return;
-  obj->picture_id = g_random_int_range (0, 1 << picture_id_bitsize);
+  gint nbits;
+
+  if (obj->picture_id_offset == -1)
+    obj->picture_id = g_random_int ();
+  else
+    obj->picture_id = obj->picture_id_offset;
+
+  nbits = picture_id_field_len (obj->picture_id_mode);
+  obj->picture_id &= (1 << nbits) - 1;
 }
 
 static void
 gst_rtp_vp8_pay_picture_id_increment (GstRtpVP8Pay * obj)
 {
-  gint picture_id_bitsize = picture_id_bitsize_from_mode (obj->picture_id_mode);
-  if (0 == picture_id_bitsize)
-      return;
-  ++obj->picture_id;
-  obj->picture_id &= (1 << picture_id_bitsize) - 1;
+  gint nbits;
+
+  if (obj->picture_id_mode == VP8_PAY_NO_PICTURE_ID)
+    return;
+
+  nbits = picture_id_field_len (obj->picture_id_mode);
+  obj->picture_id++;
+  obj->picture_id &= (1 << nbits) - 1;
 }
 
 static void
@@ -126,6 +136,7 @@ gst_rtp_vp8_pay_init (GstRtpVP8Pay * obj)
 {
   obj->picture_id_mode = DEFAULT_PICTURE_ID_MODE;
   gst_rtp_vp8_pay_picture_id_reset (obj);
+  obj->picture_id_offset = DEFAULT_PICTURE_ID_OFFSET;
 }
 
 static void
@@ -144,6 +155,18 @@ gst_rtp_vp8_pay_class_init (GstRtpVP8PayClass * gst_rtp_vp8_pay_class)
           "The picture ID mode for payloading",
           GST_TYPE_RTP_VP8_PAY_PICTURE_ID_MODE, DEFAULT_PICTURE_ID_MODE,
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+  /**
+   * rtpvp8pay:picture-id-offset:
+   *
+   * Offset to add to the initial picture-id (-1 = random)
+   *
+   * Since: 1.20
+   */
+  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_vp8_pay_sink_template);
@@ -175,6 +198,10 @@ gst_rtp_vp8_pay_set_property (GObject * object,
       rtpvp8pay->picture_id_mode = g_value_get_enum (value);
       gst_rtp_vp8_pay_picture_id_reset (rtpvp8pay);
       break;
+    case PROP_PICTURE_ID_OFFSET:
+      rtpvp8pay->picture_id_offset = g_value_get_int (value);
+      gst_rtp_vp8_pay_picture_id_reset (rtpvp8pay);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -191,6 +218,9 @@ gst_rtp_vp8_pay_get_property (GObject * object,
     case PROP_PICTURE_ID_MODE:
       g_value_set_enum (value, rtpvp8pay->picture_id_mode);
       break;
+    case PROP_PICTURE_ID_OFFSET:
+      g_value_set_int (value, rtpvp8pay->picture_id_offset);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;

gst/rtp/gstrtpvp8pay.h

@@ -62,6 +62,7 @@ struct _GstRtpVP8Pay
   guint partition_offset[10];
   guint partition_size[9];
   PictureIDMode picture_id_mode;
+  gint picture_id_offset;
   guint16 picture_id;
 };