plugins: postproc: Fix a problem of propose_allocation when passthrough.

We should query the downstream element to answer a precise allocation
query when the passthrough mode is enabled.
The current way still decides the allocation by the postproc itself. The
pipeline such as:
  gst-launch-1.0 -v filesrc location=xxx.264 ! h264parse ! vaapih264dec ! \
  vaapipostproc ! fakevideosink silent=false sync=true
will lose some info such as the GST_VIDEO_META_API_TYPE.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-vaapi/-/merge_requests/414>

1 files changed, 7 insertions, 0 deletions

diff --git a/gst/vaapi/gstvaapipostproc.c b/gst/vaapi/gstvaapipostproc.c
index 5f7d9cd8..052ee4fa 100644
--- a/gst/vaapi/gstvaapipostproc.c
+++ b/gst/vaapi/gstvaapipostproc.c
@@ -1801,6 +1801,13 @@ gst_vaapipostproc_propose_allocation (GstBaseTransform * trans,
   gint allocation_width, allocation_height;
   gint negotiated_width, negotiated_height;
 
+  /* passthrough query, we just bypass to the peer */
+  if (decide_query == NULL) {
+    return GST_BASE_TRANSFORM_CLASS
+        (gst_vaapipostproc_parent_class)->propose_allocation (trans,
+        decide_query, query);
+  }
+
   /* advertise to upstream that we can handle crop meta */
   if (decide_query)
     gst_query_add_allocation_meta (query, GST_VIDEO_CROP_META_API_TYPE, NULL);