h264decoder: use last_output_poc from DPB

It seems that `last_output_poc` in `h264decoder` class is a left over of commit
5527cc4a2e.

This patch removes it but keeps the log message by fetching the `h264picture`'s
`last_output_pic`.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4288>

subprojects/gst-plugins-bad/gst-libs/gst/codecs/gsth264decoder.c

@@ -60,6 +60,7 @@
 
 #include <gst/base/base.h>
 #include "gsth264decoder.h"
+#include "gsth264picture-private.h"
 
 GST_DEBUG_CATEGORY (gst_h264_decoder_debug);
 #define GST_CAT_DEFAULT gst_h264_decoder_debug
@@ -126,9 +127,6 @@ struct _GstH264DecoderPrivate
 
   GstH264PictureField prev_ref_field;
 
-  /* PicOrderCount of the previously outputted frame */
-  gint last_output_poc;
-
   gboolean process_ref_pic_lists;
   guint preferred_output_delay;
 
@@ -344,8 +342,6 @@ gst_h264_decoder_init (GstH264Decoder * self)
 
   self->priv = priv = gst_h264_decoder_get_instance_private (self);
 
-  priv->last_output_poc = G_MININT32;
-
   priv->ref_pic_list_p0 = g_array_sized_new (FALSE, TRUE,
       sizeof (GstH264Picture *), 32);
   g_array_set_clear_func (priv->ref_pic_list_p0,
@@ -485,7 +481,6 @@ gst_h264_decoder_clear_dpb (GstH264Decoder * self, gboolean flush)
   gst_h264_decoder_clear_ref_pic_lists (self);
   gst_clear_h264_picture (&priv->last_field);
   gst_h264_dpb_clear (priv->dpb);
-  priv->last_output_poc = G_MININT32;
 }
 
 static gboolean
@@ -1774,19 +1769,23 @@ gst_h264_decoder_do_output_picture (GstH264Decoder * self,
   GstVideoCodecFrame *frame = NULL;
   GstH264DecoderOutputFrame output_frame;
   GstFlowReturn flow_ret = GST_FLOW_OK;
+#ifndef GST_DISABLE_GST_DEBUG
+  guint32 last_output_poc;
+#endif
 
   g_assert (ret != NULL);
 
   GST_LOG_OBJECT (self, "Outputting picture %p (frame_num %d, poc %d)",
       picture, picture->frame_num, picture->pic_order_cnt);
 
-  if (picture->pic_order_cnt < priv->last_output_poc) {
+#ifndef GST_DISABLE_GST_DEBUG
+  last_output_poc = gst_h264_dpb_get_last_output_poc (priv->dpb);
+  if (picture->pic_order_cnt < last_output_poc) {
     GST_WARNING_OBJECT (self,
         "Outputting out of order %d -> %d, likely a broken stream",
-        priv->last_output_poc, picture->pic_order_cnt);
+        last_output_poc, picture->pic_order_cnt);
   }
-
-  priv->last_output_poc = picture->pic_order_cnt;
+#endif
 
   frame = gst_video_decoder_get_frame (GST_VIDEO_DECODER (self),
       picture->system_frame_number);
@@ -1878,7 +1877,6 @@ gst_h264_decoder_drain_internal (GstH264Decoder * self)
 
   gst_clear_h264_picture (&priv->last_field);
   gst_h264_dpb_clear (priv->dpb);
-  priv->last_output_poc = G_MININT32;
 
   return ret;
 }

subprojects/gst-plugins-bad/gst-libs/gst/codecs/gsth264picture-private.h

@@ -0,0 +1,28 @@
+/* GStreamer
+ * Copyright (C) <2023> The GStreamer Contributors.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#pragma once
+
+#include "gsth264picture.h"
+
+G_BEGIN_DECLS
+
+gint32 gst_h264_dpb_get_last_output_poc (GstH264Dpb * dpb);
+
+G_END_DECLS

subprojects/gst-plugins-bad/gst-libs/gst/codecs/gsth264picture.c

@@ -21,7 +21,8 @@
 #include <config.h>
 #endif
 
-#include "gsth264picture.h"
+#include "gsth264picture-private.h"
+
 #include <stdlib.h>
 
 GST_DEBUG_CATEGORY_EXTERN (gst_h264_decoder_debug);
@@ -214,6 +215,22 @@ gst_h264_dpb_get_interlaced (GstH264Dpb * dpb)
   return dpb->interlaced;
 }
 
+/**
+ * gst_h264_dpb_get_last_output_poc:
+ * @dpb: a #GstH264Dpb
+ *
+ * Returns: the last outputted picture order count
+ *
+ * Since: 1.24
+ */
+gint32
+gst_h264_dpb_get_last_output_poc (GstH264Dpb * dpb)
+{
+  g_return_val_if_fail (dpb != NULL, G_MININT32);
+
+  return dpb->last_output_poc;
+}
+
 /**
  * gst_h264_dpb_free:
  * @dpb: a #GstH264Dpb to free