context: allow dynamic growth of VA surfaces pool.

Add support for dynamic growth of the VA surfaces pool. For decoding,
this implies the recreation of the underlying VA context, as per the
requirement from VA-API. Besides, only increases are supported, not
shrinks.

gst-libs/gst/vaapi/gstvaapicontext.c

@@ -47,6 +47,9 @@
 /* Define default VA surface chroma format to YUV 4:2:0 */
 #define DEFAULT_CHROMA_TYPE (GST_VAAPI_CHROMA_TYPE_YUV420)
 
+/* Number of scratch surfaces beyond those used as reference */
+#define SCRATCH_SURFACES_COUNT (4)
+
 static void
 unref_surface_cb (GstVaapiSurface * surface)
 {
@@ -105,16 +108,34 @@ context_destroy (GstVaapiContext * context)
   }
 }
 
+static gboolean
+context_ensure_surfaces (GstVaapiContext * context)
+{
+  const GstVaapiContextInfo *const cip = &context->info;
+  const guint num_surfaces = cip->ref_frames + SCRATCH_SURFACES_COUNT;
+  GstVaapiSurface *surface;
+  guint i;
+
+  for (i = context->surfaces->len; i < num_surfaces; i++) {
+    surface = gst_vaapi_surface_new (GST_VAAPI_OBJECT_DISPLAY (context),
+        cip->chroma_type, cip->width, cip->height);
+    if (!surface)
+      return FALSE;
+    gst_vaapi_surface_set_parent_context (surface, context);
+    g_ptr_array_add (context->surfaces, surface);
+    if (!gst_vaapi_video_pool_add_object (context->surfaces_pool, surface))
+      return FALSE;
+  }
+  gst_vaapi_video_pool_set_capacity (context->surfaces_pool, num_surfaces);
+  return TRUE;
+}
+
 static gboolean
 context_create_surfaces (GstVaapiContext * context)
 {
   const GstVaapiContextInfo *const cip = &context->info;
   GstVideoInfo vi;
-  GstVaapiSurface *surface;
+  guint num_surfaces;
-  guint i, num_surfaces;
-
-  /* Number of scratch surfaces beyond those used as reference */
-  const guint SCRATCH_SURFACES_COUNT = 4;
 
   if (!gst_vaapi_context_overlay_reset (context))
     return FALSE;
@@ -135,19 +156,7 @@ context_create_surfaces (GstVaapiContext * context)
     if (!context->surfaces_pool)
       return FALSE;
   }
-  gst_vaapi_video_pool_set_capacity (context->surfaces_pool, num_surfaces);
+  return context_ensure_surfaces (context);
-
-  for (i = context->surfaces->len; i < num_surfaces; i++) {
-    surface = gst_vaapi_surface_new (GST_VAAPI_OBJECT_DISPLAY (context),
-        cip->chroma_type, cip->width, cip->height);
-    if (!surface)
-      return FALSE;
-    gst_vaapi_surface_set_parent_context (surface, context);
-    g_ptr_array_add (context->surfaces, surface);
-    if (!gst_vaapi_video_pool_add_object (context->surfaces_pool, surface))
-      return FALSE;
-  }
-  return TRUE;
 }
 
 static gboolean
@@ -370,6 +379,7 @@ gst_vaapi_context_reset (GstVaapiContext * context,
 {
   GstVaapiContextInfo *const cip = &context->info;
   gboolean reset_surfaces = FALSE, reset_config = FALSE;
+  gboolean grow_surfaces = FALSE;
   GstVaapiChromaType chroma_type;
 
   chroma_type = new_cip->chroma_type ? new_cip->chroma_type :
@@ -392,6 +402,11 @@ gst_vaapi_context_reset (GstVaapiContext * context,
     reset_config = TRUE;
   }
 
+  if (cip->ref_frames < new_cip->ref_frames) {
+    cip->ref_frames = new_cip->ref_frames;
+    grow_surfaces = TRUE;
+  }
+
   if (cip->usage != new_cip->usage) {
     cip->usage = new_cip->usage;
     reset_config = TRUE;
@@ -400,7 +415,7 @@ gst_vaapi_context_reset (GstVaapiContext * context,
     if (context_update_config_encoder (context, &new_cip->config.encoder))
       reset_config = TRUE;
   } else if (new_cip->usage == GST_VAAPI_CONTEXT_USAGE_DECODE) {
-    if (reset_surfaces)
+    if (reset_surfaces || grow_surfaces)
       reset_config = TRUE;
   }
 
@@ -411,6 +426,8 @@ gst_vaapi_context_reset (GstVaapiContext * context,
 
   if (reset_surfaces && !context_create_surfaces (context))
     return FALSE;
+  else if (grow_surfaces && !context_ensure_surfaces (context))
+    return FALSE;
   if (reset_config && !context_create (context))
     return FALSE;
   return TRUE;