refactor: introduce keypoint descriptors and switch skeleton connecti…

…ons to integer indices

Add a shared C header (gstanalyticskeypointdescriptor.h) that defines
keypoint format descriptors — typed structs mapping a semantic_tag to
keypoint names and skeleton connections as integer index pairs.
Three built-in descriptors are provided: COCO-17, OpenPose-18, and
CenterFace-5.

Key changes:

- Skeleton connections are now uint32_t index pairs instead of
  string name pairs throughout the pipeline (converters, watermark,
  metaconvert, tensor round-trip).

- convert_to_meta (tensor.h): reads skeleton from the descriptor
  directly (zero-copy pointer) instead of parsing string arrays.
  Removed ClsMtd-based point_names metadata layer — names are now
  resolved from the descriptor at read time.

- convert_to_tensor (tensor.h): looks up point_names from the
  descriptor via semantic_tag. Skeleton is still reconstructed from
  RELATE_TO relations. point_names and point_connections fields are
  only emitted when non-empty.

- yolo_v8.cpp, yolo_v26.cpp: replaced local name/connection string
  vectors with a reference to the COCO-17 descriptor.

- centerface.cpp: uses CenterFace-5 descriptor; emits per-keypoint
  confidence as GST_TYPE_ARRAY (float vector) instead of a single
  G_TYPE_DOUBLE, fixing downstream consumers that expect an array.

- gvawatermark: preparePrimsForKeypointConnections rewritten to read
  uint32_t indices via gst_value_array_* API. Removed unused
  get_keypoint_index_by_name helper.

- gvametaconvert: attach_gvaluearray_to_json rewritten to use
  gst_value_array_* API and handle multiple GValue types (string,
  uint, int, float).

- keypoints.h (base converter): sets GstStructure name and type to
  "keypoints" in createTensor(); removed redundant format field.

- blob_to_roi_converter.h, region_of_interest.h: filter keypoints
  tensors by type== instead of name==.

include/dlstreamer/gst/metadata/gstanalyticskeypointdescriptor.h

@@ -0,0 +1,191 @@
+/*******************************************************************************
+ * Copyright (C) 2026 Intel Corporation
+ *
+ * SPDX-License-Identifier: MIT
+ ******************************************************************************/
+
+#ifndef __GST_ANALYTICS_KEYPOINT_DESCRIPTOR_H__
+#define __GST_ANALYTICS_KEYPOINT_DESCRIPTOR_H__
+
+#include <stddef.h>
+
+/**
+ * GstAnalyticsKeypointDescriptor:
+ * @semantic_tag: Unique identifier string for this keypoint format.
+ * @point_names: Array of keypoint name strings.
+ * @point_count: Number of keypoints in @point_names.
+ * @skeleton_connections: Array of int pairs (index_a, index_b) into
+ *   @point_names describing the skeleton edges. Length is
+ *   @skeleton_connection_count * 2.
+ * @skeleton_connection_count: Number of skeleton connection pairs.
+ *
+ * Descriptor that associates a semantic tag with a set of keypoint names
+ * and their skeleton connections, so that code consuming keypoint metadata
+ * can look up the layout by tag.
+ */
+typedef struct {
+    const char *semantic_tag;
+    const char *const *point_names;
+    size_t point_count;
+    const int *skeleton_connections;
+    size_t skeleton_connection_count;
+} GstAnalyticsKeypointDescriptor;
+
+/*
+ * COCO 17-keypoint body pose
+ *
+ * Keypoint indices:
+ *   0  nose           1  eye_l          2  eye_r
+ *   3  ear_l          4  ear_r          5  shoulder_l
+ *   6  shoulder_r     7  elbow_l        8  elbow_r
+ *   9  wrist_l       10  wrist_r       11  hip_l
+ *  12  hip_r         13  knee_l        14  knee_r
+ *  15  ankle_l       16  ankle_r
+ */
+
+#define GST_ANALYTICS_KEYPOINT_BODY_POSE_COCO_17 "body-pose/coco-17"
+
+static const char *const _gst_keypoint_coco17_point_names[] = {
+    "nose",    "eye_l",   "eye_r",  "ear_l",  "ear_r",
+    "shoulder_l", "shoulder_r", "elbow_l", "elbow_r",
+    "wrist_l", "wrist_r", "hip_l",  "hip_r",
+    "knee_l",  "knee_r",  "ankle_l", "ankle_r"
+};
+
+/* Each consecutive pair of ints is (from, to) using the indices above. */
+static const int _gst_keypoint_coco17_skeleton[] = {
+     0,  1,  /* nose        - eye_l       */
+     0,  2,  /* nose        - eye_r       */
+     1,  3,  /* eye_l       - ear_l       */
+     2,  4,  /* eye_r       - ear_r       */
+     3,  5,  /* ear_l       - shoulder_l  */
+     4,  6,  /* ear_r       - shoulder_r  */
+     5,  6,  /* shoulder_l  - shoulder_r  */
+     5,  7,  /* shoulder_l  - elbow_l     */
+     6,  8,  /* shoulder_r  - elbow_r     */
+     7,  9,  /* elbow_l     - wrist_l     */
+     8, 10,  /* elbow_r     - wrist_r     */
+     5, 11,  /* shoulder_l  - hip_l       */
+     6, 12,  /* shoulder_r  - hip_r       */
+    11, 12,  /* hip_l       - hip_r       */
+    11, 13,  /* hip_l       - knee_l      */
+    12, 14,  /* hip_r       - knee_r      */
+    13, 15,  /* knee_l      - ankle_l     */
+    14, 16   /* knee_r      - ankle_r     */
+};
+
+static const GstAnalyticsKeypointDescriptor gst_keypoint_descriptor_coco17 = {
+    GST_ANALYTICS_KEYPOINT_BODY_POSE_COCO_17,
+    _gst_keypoint_coco17_point_names,
+    17,
+    _gst_keypoint_coco17_skeleton,
+    18
+};
+
+/*
+ * OpenPose 18-keypoint body pose (COCO + neck)
+ *
+ * Keypoint indices:
+ *   0  nose           1  neck           2  shoulder_r
+ *   3  elbow_r        4  wrist_r        5  shoulder_l
+ *   6  elbow_l        7  wrist_l        8  hip_r
+ *   9  knee_r        10  ankle_r       11  hip_l
+ *  12  knee_l        13  ankle_l       14  eye_r
+ *  15  eye_l         16  ear_r         17  ear_l
+ */
+
+#define GST_ANALYTICS_KEYPOINT_BODY_POSE_OPENPOSE_18 "body-pose/openpose-18"
+
+static const char *const _gst_keypoint_openpose18_point_names[] = {
+    "nose",       "neck",       "shoulder_r", "elbow_r",  "wrist_r",
+    "shoulder_l", "elbow_l",    "wrist_l",    "hip_r",    "knee_r",
+    "ankle_r",    "hip_l",      "knee_l",     "ankle_l",
+    "eye_r",      "eye_l",      "ear_r",      "ear_l"
+};
+
+/* Skeleton from OpenPose limb_ids_heatmap (peak.cpp). */
+static const int _gst_keypoint_openpose18_skeleton[] = {
+     1,  2,  /* neck        - shoulder_r  */
+     1,  5,  /* neck        - shoulder_l  */
+     2,  3,  /* shoulder_r  - elbow_r     */
+     3,  4,  /* elbow_r     - wrist_r     */
+     5,  6,  /* shoulder_l  - elbow_l     */
+     6,  7,  /* elbow_l     - wrist_l     */
+     1,  8,  /* neck        - hip_r       */
+     8,  9,  /* hip_r       - knee_r      */
+     9, 10,  /* knee_r      - ankle_r     */
+     1, 11,  /* neck        - hip_l       */
+    11, 12,  /* hip_l       - knee_l      */
+    12, 13,  /* knee_l      - ankle_l     */
+     1,  0,  /* neck        - nose        */
+     0, 14,  /* nose        - eye_r       */
+    14, 16,  /* eye_r       - ear_r       */
+     0, 15,  /* nose        - eye_l       */
+    15, 17   /* eye_l       - ear_l       */
+};
+
+static const GstAnalyticsKeypointDescriptor gst_keypoint_descriptor_openpose18 = {
+    GST_ANALYTICS_KEYPOINT_BODY_POSE_OPENPOSE_18,
+    _gst_keypoint_openpose18_point_names,
+    18,
+    _gst_keypoint_openpose18_skeleton,
+    17
+};
+
+/*
+ * CenterFace 5-point facial landmarks
+ *
+ * Keypoint indices:
+ *   0  eye_l          1  eye_r          2  nose_tip
+ *   3  mouth_l        4  mouth_r
+ */
+
+#define GST_ANALYTICS_KEYPOINT_FACE_CENTERFACE_5 "face-landmarks/centerface-5"
+
+static const char *const _gst_keypoint_centerface5_point_names[] = {
+    "eye_l", "eye_r", "nose_tip", "mouth_l", "mouth_r"
+};
+
+static const GstAnalyticsKeypointDescriptor gst_keypoint_descriptor_centerface5 = {
+    GST_ANALYTICS_KEYPOINT_FACE_CENTERFACE_5,
+    _gst_keypoint_centerface5_point_names,
+    5,
+    NULL,
+    0
+};
+
+/* Registry of all known keypoint descriptors. Add new entries here. */
+static const GstAnalyticsKeypointDescriptor *const _gst_keypoint_descriptors[] = {
+    &gst_keypoint_descriptor_coco17,
+    &gst_keypoint_descriptor_openpose18,
+    &gst_keypoint_descriptor_centerface5,
+    NULL
+};
+
+/**
+ * gst_analytics_keypoint_descriptor_find_by_tag:
+ * @semantic_tag: The tag to look up.
+ *
+ * Search all known keypoint descriptors for a matching @semantic_tag.
+ *
+ * Returns: pointer to the matching descriptor, or %NULL if not found.
+ */
+static inline const GstAnalyticsKeypointDescriptor *
+gst_analytics_keypoint_descriptor_find_by_tag(const char *semantic_tag)
+{
+    if (!semantic_tag)
+        return NULL;
+    const GstAnalyticsKeypointDescriptor *const *it = _gst_keypoint_descriptors;
+    for (; *it; ++it) {
+        const char *a = (*it)->semantic_tag;
+        const char *b = semantic_tag;
+        if (a) {
+            while (*a && *a == *b) { ++a; ++b; }
+            if (*a == '\0' && *b == '\0')
+                return *it;
+        }
+    }
+    return NULL;
+}
+
+#endif /* __GST_ANALYTICS_KEYPOINT_DESCRIPTOR_H__ */

include/dlstreamer/gst/videoanalytics/region_of_interest.h

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (C) 2018-2025 Intel Corporation
+ * Copyright (C) 2018-2026 Intel Corporation
  *
  * SPDX-License-Identifier: MIT
  ******************************************************************************/
@@ -231,7 +231,7 @@ class RegionOfInterest {
         for (GList *l = meta->params; l; l = g_list_next(l)) {
             GstStructure *s = GST_STRUCTURE(l->data);
             const char *type = gst_structure_get_string(s, "type");
-            if (not gst_structure_has_name(s, "object_id") && not gst_structure_has_name(s, "keypoints") &&
+            if (not gst_structure_has_name(s, "object_id") && (type == nullptr || strcmp(type, "keypoints") != 0) &&
                 (type == nullptr || strcmp(type, "classification_result") != 0)) {
                 _tensors.emplace_back(s);
                 if (_tensors.back().is_detection())