h264decoder: Add ability to lookup by system_frame_number

This is to avoid having to create a reference chain in decoders from
GstVideoCodecFrame to GstH264PIcture to implementation wrapper.

So this change introduces:

 - gst_h264_dpb_remove_outputed (dpb)
 - gst_h264_dpb_get_picture(dpb, system_frame_num)
 - gst_h264_decoder_get_picture (dec, system_frame_num)

In order to ensure that frames can be looked up during the draining
process, we now first remove all (including reference) frames that
have been outputed but are still in the DPB. Then for each remaining
buffers, we remove it from the DPB to reach reference 1 and output it.

Previously we could take all not outputed outside of the DPB which would
prevent lookup by the base class.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1449>

gst-libs/gst/codecs/gsth264decoder.c

@@ -1320,15 +1320,20 @@ gst_h264_decoder_drain_internal (GstH264Decoder * self)
   GstH264DecoderPrivate *priv = self->priv;
   GArray *to_output = priv->to_output;
 
+  /* We are around to drain, so we can get rist of everything that has been
+   * outputed already */
+  gst_h264_dpb_delete_outputed (priv->dpb);
   gst_h264_dpb_get_pictures_not_outputted (priv->dpb, to_output);
   g_array_sort (to_output, (GCompareFunc) poc_asc_compare);
-  gst_h264_dpb_clear (priv->dpb);
 
   while (to_output->len) {
     GstH264Picture *picture = g_array_index (to_output, GstH264Picture *, 0);
 
+    /* We want the last reference when outputing so take a ref and then remove
+     * from both arrays. */
     gst_h264_picture_ref (picture);
     g_array_remove_index (to_output, 0);
+    gst_h264_dpb_delete_by_poc (priv->dpb, picture->pic_order_cnt);
 
     GST_LOG_OBJECT (self, "Output picture %p (frame num %d, poc %d)", picture,
         picture->frame_num, picture->pic_order_cnt);
@@ -1336,6 +1341,8 @@ gst_h264_decoder_drain_internal (GstH264Decoder * self)
   }
 
   g_array_set_size (to_output, 0);
+  gst_h264_dpb_clear (priv->dpb);
+  priv->last_output_poc = 0;
   return TRUE;
 }
 
@@ -2456,3 +2463,10 @@ gst_h264_decoder_set_process_ref_pic_lists (GstH264Decoder * self,
 {
   self->priv->process_ref_pic_lists = process;
 }
+
+GstH264Picture *
+gst_h264_decoder_get_picture (GstH264Decoder * self,
+    guint32 system_frame_number)
+{
+  return gst_h264_dpb_get_picture (self->priv->dpb, system_frame_number);
+}

gst-libs/gst/codecs/gsth264decoder.h

@@ -139,6 +139,10 @@ GST_CODECS_API
 void gst_h264_decoder_set_process_ref_pic_lists (GstH264Decoder * self,
                                                  gboolean process);
 
+GST_CODECS_API
+GstH264Picture * gst_h264_decoder_get_picture   (GstH264Decoder * self,
+                                                 guint32 system_frame_number);
+
 G_END_DECLS
 
 #endif /* __GST_H264_DECODER_H__ */

gst-libs/gst/codecs/gsth264picture.c

@@ -233,6 +233,32 @@ gst_h264_dpb_delete_unused (GstH264Dpb * dpb)
   }
 }
 
+/**
+ * gst_h264_dpb_delete_outputed:
+ * @dpb: a #GstH264Dpb
+ *
+ * Delete already outputted picture, even if they are referenced.
+ */
+void
+gst_h264_dpb_delete_outputed (GstH264Dpb * dpb)
+{
+  gint i;
+
+  g_return_if_fail (dpb != NULL);
+
+  for (i = 0; i < dpb->pic_list->len; i++) {
+    GstH264Picture *picture =
+        g_array_index (dpb->pic_list, GstH264Picture *, i);
+
+    if (picture->outputted) {
+      GST_TRACE ("remove picture %p (frame num %d) from dpb",
+          picture, picture->frame_num);
+      g_array_remove_index_fast (dpb->pic_list, i);
+      i--;
+    }
+  }
+}
+
 /**
  * gst_h264_dpb_delete_by_poc:
  * @dpb: a #GstH264Dpb
@@ -523,3 +549,29 @@ gst_h264_dpb_is_full (GstH264Dpb * dpb)
 
   return dpb->pic_list->len >= dpb->max_num_pics;
 }
+
+/**
+ * gst_h264_dpb_get_picture:
+ * @system_frame_number The system frame number
+ *
+ * Returns: the picture identitifed with the specified @system_frame_number.
+ */
+GstH264Picture *
+gst_h264_dpb_get_picture (GstH264Dpb * dpb, guint32 system_frame_number)
+{
+  gint i;
+
+  g_return_val_if_fail (dpb != NULL, NULL);
+
+  for (i = 0; i < dpb->pic_list->len; i++) {
+    GstH264Picture *picture =
+        g_array_index (dpb->pic_list, GstH264Picture *, i);
+
+    if (picture->system_frame_number == system_frame_number) {
+      gst_h264_picture_ref (picture);
+      return picture;
+    }
+  }
+
+  return NULL;
+}

gst-libs/gst/codecs/gsth264picture.h

@@ -169,6 +169,9 @@ void  gst_h264_dpb_add              (GstH264Dpb * dpb,
 GST_CODECS_API
 void  gst_h264_dpb_delete_unused    (GstH264Dpb * dpb);
 
+GST_CODECS_API
+void gst_h264_dpb_delete_outputed   (GstH264Dpb * dpb);
+
 GST_CODECS_API
 void  gst_h264_dpb_delete_by_poc    (GstH264Dpb * dpb,
                                      gint poc);
@@ -205,6 +208,10 @@ void  gst_h264_dpb_get_pictures_long_term_ref  (GstH264Dpb * dpb,
 GST_CODECS_API
 GArray * gst_h264_dpb_get_pictures_all         (GstH264Dpb * dpb);
 
+GST_CODECS_API
+GstH264Picture * gst_h264_dpb_get_picture      (GstH264Dpb * dpb,
+                                                guint32 system_frame_number);
+
 GST_CODECS_API
 gint  gst_h264_dpb_get_size   (GstH264Dpb * dpb);