avfilter/framequeue: add support for limiting and tracking buffered frames in the queues

Signed-off-by: Marton Balint <cus@passwd.hu>

libavfilter/framequeue.h

@@ -40,11 +40,18 @@ typedef struct FFFrameBucket {
  *
  * This structure is intended to allow implementing global control of the
  * frame queues, including memory consumption caps.
- *
- * It is currently empty.
  */
 typedef struct FFFrameQueueGlobal {
-    char dummy; /* C does not allow empty structs */
+
+    /**
+     * Maximum number of allowed frames in the queues combined.
+     */
+    size_t max_queued;
+
+    /**
+     * Total number of queued frames in the queues combined.
+     */
+    size_t queued;
 } FFFrameQueueGlobal;
 
 /**
@@ -52,6 +59,11 @@ typedef struct FFFrameQueueGlobal {
  */
 typedef struct FFFrameQueue {
 
+    /**
+     * Pointer to the global frame queue struct holding statistics and limits
+     */
+    FFFrameQueueGlobal *global;
+
     /**
      * Array of allocated buckets, used as a circular buffer.
      */