v4l2codec: h264: Implement support for split fields

When a frame is composed of two fields, the base class now split the
picture in two. In order to support this, we need to ensure that picture
buffer is held in VB2 queue so that the second field get decoded into
it. This also implements the new_field_picture() virtual and sets the
previous request on the new picture.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2474>

1 files changed, 33 insertions, 1 deletions

diff --git a/sys/v4l2codecs/gstv4l2codech264dec.c b/sys/v4l2codecs/gstv4l2codech264dec.c
index 5c912edca..bd482b585 100644
--- a/sys/v4l2codecs/gstv4l2codech264dec.c
+++ b/sys/v4l2codecs/gstv4l2codech264dec.c
@@ -1216,7 +1216,37 @@ gst_v4l2_codec_h264_dec_end_picture (GstH264Decoder * decoder,
     GstH264Picture * picture)
 {
   GstV4l2CodecH264Dec *self = GST_V4L2_CODEC_H264_DEC (decoder);
-  return gst_v4l2_codec_h264_dec_submit_bitstream (self, picture, 0);
+  guint flags = 0;
+
+  /* Hold on the output frame if this is first field of a pair */
+  if (picture->field != GST_H264_PICTURE_FIELD_FRAME && !picture->second_field)
+    flags = V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;
+
+  return gst_v4l2_codec_h264_dec_submit_bitstream (self, picture, flags);
+}
+
+static gboolean
+gst_v4l2_codec_h264_dec_new_field_picture (GstH264Decoder * decoder,
+    const GstH264Picture * first_field, GstH264Picture * second_field)
+{
+  GstV4l2CodecH264Dec *self = GST_V4L2_CODEC_H264_DEC (decoder);
+  GstV4l2Request *request =
+      gst_h264_picture_get_user_data ((GstH264Picture *) first_field);
+
+  if (!request) {
+    GST_WARNING_OBJECT (self,
+        "First picture does not have an associated request");
+    return TRUE;
+  }
+
+  GST_DEBUG_OBJECT (self, "Assigned request %p to second field.", request);
+
+  /* Associate the previous request with the new picture so that
+   * submit_bitstream can create sub-request */
+  gst_h264_picture_set_user_data (second_field, gst_v4l2_request_ref (request),
+      (GDestroyNotify) gst_v4l2_request_unref);
+
+  return TRUE;
 }
 
 static guint
@@ -1393,6 +1423,8 @@ gst_v4l2_codec_h264_dec_subclass_init (GstV4l2CodecH264DecClass * klass,
       GST_DEBUG_FUNCPTR (gst_v4l2_codec_h264_dec_decode_slice);
   h264decoder_class->end_picture =
       GST_DEBUG_FUNCPTR (gst_v4l2_codec_h264_dec_end_picture);
+  h264decoder_class->new_field_picture =
+      GST_DEBUG_FUNCPTR (gst_v4l2_codec_h264_dec_new_field_picture);
   h264decoder_class->get_preferred_output_delay =
       GST_DEBUG_FUNCPTR (gst_v4l2_codec_h264_dec_get_preferred_output_delay);