pthread_frame: introduce a codec callback to update the user-facing context

libavcodec/codec.h

@@ -258,6 +258,11 @@ typedef struct AVCodec {
      * dst and src will (rarely) point to the same context, in which case memcpy should be skipped.
      */
     int (*update_thread_context)(struct AVCodecContext *dst, const struct AVCodecContext *src);
+
+    /**
+     * Copy variables back to the user-facing context
+     */
+    int (*update_thread_context_for_user)(struct AVCodecContext *dst, const struct AVCodecContext *src);
     /** @} */
 
     /**

libavcodec/pthread_frame.c

@@ -326,6 +326,8 @@ FF_DISABLE_DEPRECATION_WARNINGS
         dst->coded_frame = src->coded_frame;
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
+        if (dst->codec->update_thread_context_for_user)
+            err = dst->codec->update_thread_context_for_user(dst, src);
     } else {
         if (dst->codec->update_thread_context)
             err = dst->codec->update_thread_context(dst, src);