v4l2codecs: gstv4l2codecsvp8dec: implement a render delay

The v4l2 backend support delayed output for performance reasons.
It is then possible to use render delays to queue multiple requests
simultaneously, thus increasing performance.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2150>

1 files changed, 25 insertions, 1 deletions

diff --git a/sys/v4l2codecs/gstv4l2codecvp8dec.c b/sys/v4l2codecs/gstv4l2codecvp8dec.c
index 4abcbfcae..dcda996d0 100644
--- a/sys/v4l2codecs/gstv4l2codecvp8dec.c
+++ b/sys/v4l2codecs/gstv4l2codecvp8dec.c
@@ -82,6 +82,24 @@ G_DEFINE_ABSTRACT_TYPE_WITH_CODE (GstV4l2CodecVp8Dec,
         "V4L2 stateless VP8 decoder"));
 #define parent_class gst_v4l2_codec_vp8_dec_parent_class
 
+static guint
+gst_v4l2_codec_vp8_dec_get_preferred_output_delay (GstVp8Decoder * decoder,
+    gboolean is_live)
+{
+
+  GstV4l2CodecVp8Dec *self = GST_V4L2_CODEC_VP8_DEC (decoder);
+  guint delay;
+
+  if (is_live)
+    delay = 0;
+  else
+    /* Just one for now, perhaps we can make this configurable in the future. */
+    delay = 1;
+
+  gst_v4l2_decoder_set_render_delay (self->decoder, delay);
+  return delay;
+}
+
 static gboolean
 gst_v4l2_codec_vp8_dec_open (GstVideoDecoder * decoder)
 {
@@ -240,6 +258,7 @@ gst_v4l2_codec_vp8_dec_decide_allocation (GstVideoDecoder * decoder,
 {
   GstV4l2CodecVp8Dec *self = GST_V4L2_CODEC_VP8_DEC (decoder);
   guint min = 0;
+  guint num_bitstream;
 
   self->has_videometa = gst_query_find_allocation_meta (query,
       GST_VIDEO_META_API_TYPE, NULL);
@@ -252,8 +271,11 @@ gst_v4l2_codec_vp8_dec_decide_allocation (GstVideoDecoder * decoder,
 
   min = MAX (2, min);
 
+  num_bitstream = 1 +
+      MAX (1, gst_v4l2_decoder_get_render_delay (self->decoder));
+
   self->sink_allocator = gst_v4l2_codec_allocator_new (self->decoder,
-      GST_PAD_SINK, 2);
+      GST_PAD_SINK, num_bitstream);
   self->src_allocator = gst_v4l2_codec_allocator_new (self->decoder,
       GST_PAD_SRC, self->min_pool_size + min + 4);
   self->src_pool = gst_v4l2_codec_pool_new (self->src_allocator, &self->vinfo);
@@ -850,6 +872,8 @@ gst_v4l2_codec_vp8_dec_subclass_init (GstV4l2CodecVp8DecClass * klass,
       GST_DEBUG_FUNCPTR (gst_v4l2_codec_vp8_dec_end_picture);
   vp8decoder_class->output_picture =
       GST_DEBUG_FUNCPTR (gst_v4l2_codec_vp8_dec_output_picture);
+  vp8decoder_class->get_preferred_output_delay =
+      GST_DEBUG_FUNCPTR (gst_v4l2_codec_vp8_dec_get_preferred_output_delay);
 
   klass->device = device;
   gst_v4l2_decoder_install_properties (gobject_class, PROP_LAST, device);