obu: check that the frame referenced by existing_frame_idx is showable

From section 6.8.2 in the AV1 spec:

"It is a requirement of bitstream conformance that when show_existing_frame
is used to show a previous frame, that the value of showable_frame for the
previous frame was equal to 1."

1 files changed, 6 insertions, 0 deletions

diff --git a/src/obu.c b/src/obu.c
index 4145988..d0f8fcf 100644
--- a/src/obu.c
+++ b/src/obu.c
@@ -396,6 +396,7 @@ static int parse_frame_hdr(Dav1dContext *const c, GetBits *const gb) {
     if (hdr->show_frame) {
         if (seqhdr->decoder_model_info_present && !seqhdr->equal_picture_interval)
             hdr->frame_presentation_delay = dav1d_get_bits(gb, seqhdr->frame_presentation_delay_length);
+        hdr->showable_frame = hdr->frame_type != DAV1D_FRAME_TYPE_KEY;
     } else
         hdr->showable_frame = dav1d_get_bits(gb, 1);
     hdr->error_resilient_mode =
@@ -1556,6 +1557,11 @@ int dav1d_parse_obus(Dav1dContext *const c, Dav1dData *const in, const int globa
     if (c->seq_hdr && c->frame_hdr) {
         if (c->frame_hdr->show_existing_frame) {
             if (!c->refs[c->frame_hdr->existing_frame_idx].p.p.data[0]) goto error;
+            if (c->strict_std_compliance &&
+                !c->refs[c->frame_hdr->existing_frame_idx].p.p.frame_hdr->showable_frame)
+            {
+                goto error;
+            }
             if (c->n_fc == 1) {
                 dav1d_thread_picture_ref(&c->out,
                                          &c->refs[c->frame_hdr->existing_frame_idx].p);