codecalphademux: Fix handling of flow combine

As the alphacombine is simplified to received matching pair of buffers,
we can't just stop streaming when we receive EOS from downstream. Due
to usage of queue, the moment we get this return value may differ.

Though, by continuing pushing, we override the last_flowret on the pad
which can make us miss that we effectively can combine all flow into
EOS.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2238>

1 files changed, 28 insertions, 7 deletions

diff --git a/gst/codecalpha/gstcodecalphademux.c b/gst/codecalpha/gstcodecalphademux.c
index bb0b0ca7f..80f668453 100644
--- a/gst/codecalpha/gstcodecalphademux.c
+++ b/gst/codecalpha/gstcodecalphademux.c
@@ -102,25 +102,46 @@ gst_codec_alpha_demux_chain (GstPad * pad, GstObject * object,
   GstClockTime pts = GST_BUFFER_PTS (buffer);
   GstClockTime duration = GST_BUFFER_DURATION (buffer);
   GstFlowReturn ret;
+  gboolean src_pad_eos, alpha_pad_eos;
 
   if (alpha_meta)
     alpha_buffer = gst_buffer_ref (alpha_meta->buffer);
 
-  ret = gst_flow_combiner_update_pad_flow (self->flow_combiner,
-      self->src_pad, gst_pad_push (self->src_pad, buffer));
+  /* To satisfy the alphacombine requirement, we need to push in pair here, so we
+   * can't just stop pushing at EOS. For this reason, remember if pad had a
+   * flow return of EOS and set it back if needed. */
+  src_pad_eos = (GST_PAD_LAST_FLOW_RETURN (self->src_pad) == GST_FLOW_EOS);
+  alpha_pad_eos = (GST_PAD_LAST_FLOW_RETURN (self->alpha_pad) == GST_FLOW_EOS);
+
+  if (src_pad_eos && alpha_pad_eos) {
+    gst_buffer_unref (alpha_buffer);
+    gst_buffer_unref (buffer);
+    return GST_FLOW_EOS;
+  }
+
+  ret = gst_pad_push (self->src_pad, buffer);
 
   /* we lost ownership here */
   buffer = NULL;
   alpha_meta = NULL;
 
+  if (ret == GST_FLOW_OK && src_pad_eos)
+    gst_flow_combiner_update_pad_flow (self->flow_combiner, self->src_pad,
+        GST_FLOW_EOS);
+  else
+    gst_flow_combiner_update_flow (self->flow_combiner, ret);
+
   if (alpha_buffer)
-    ret = gst_flow_combiner_update_pad_flow (self->flow_combiner,
-        self->alpha_pad, gst_pad_push (self->alpha_pad, alpha_buffer));
+    ret = gst_pad_push (self->alpha_pad, alpha_buffer);
   else
-    ret = gst_flow_combiner_update_pad_flow (self->flow_combiner,
-        self->alpha_pad, gst_pad_push_event (self->alpha_pad,
-            gst_event_new_gap (pts, duration)));
+    ret = gst_pad_push_event (self->alpha_pad,
+        gst_event_new_gap (pts, duration));
 
+  if (ret == GST_FLOW_OK && alpha_pad_eos)
+    ret = gst_flow_combiner_update_pad_flow (self->flow_combiner,
+        self->alpha_pad, GST_FLOW_EOS);
+  else
+    ret = gst_flow_combiner_update_flow (self->flow_combiner, ret);
 
   return ret;
 }