avcodec/av1dec: expose skip mode frame index

Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>
Co-authored-by: James Almer <jamrial@gmail.com>

libavcodec/av1dec.c

@@ -145,6 +145,78 @@ static void global_motion_params(AV1DecContext *s)
     }
 }
 
+static int get_relative_dist(const AV1RawSequenceHeader *seq,
+                             unsigned int a, unsigned int b)
+{
+    unsigned int diff = a - b;
+    unsigned int m = 1 << seq->order_hint_bits_minus_1;
+    return (diff & (m - 1)) - (diff & m);
+}
+
+static void skip_mode_params(AV1DecContext *s)
+{
+    const AV1RawFrameHeader *header = s->raw_frame_header;
+    const AV1RawSequenceHeader *seq = s->raw_seq;
+
+    int forward_idx,  backward_idx;
+    int forward_hint, backward_hint;
+    int second_forward_idx, second_forward_hint;
+    int ref_hint, dist, i;
+
+    if (!header->skip_mode_present)
+        return;
+
+    forward_idx  = -1;
+    backward_idx = -1;
+    for (i = 0; i < AV1_REFS_PER_FRAME; i++) {
+        ref_hint = s->ref[header->ref_frame_idx[i]].order_hint;
+        dist = get_relative_dist(seq, ref_hint, header->order_hint);
+        if (dist < 0) {
+            if (forward_idx < 0 ||
+                get_relative_dist(seq, ref_hint, forward_hint) > 0) {
+                forward_idx  = i;
+                forward_hint = ref_hint;
+            }
+        } else if (dist > 0) {
+            if (backward_idx < 0 ||
+                get_relative_dist(seq, ref_hint, backward_hint) < 0) {
+                backward_idx  = i;
+                backward_hint = ref_hint;
+            }
+        }
+    }
+
+    if (forward_idx < 0) {
+        return;
+    } else if (backward_idx >= 0) {
+        s->cur_frame.skip_mode_frame_idx[0] =
+            AV1_REF_FRAME_LAST + FFMIN(forward_idx, backward_idx);
+        s->cur_frame.skip_mode_frame_idx[1] =
+            AV1_REF_FRAME_LAST + FFMAX(forward_idx, backward_idx);
+        return;
+    }
+
+    second_forward_idx = -1;
+    for (i = 0; i < AV1_REFS_PER_FRAME; i++) {
+        ref_hint = s->ref[header->ref_frame_idx[i]].order_hint;
+        if (get_relative_dist(seq, ref_hint, forward_hint) < 0) {
+            if (second_forward_idx < 0 ||
+                get_relative_dist(seq, ref_hint, second_forward_hint) > 0) {
+                second_forward_idx  = i;
+                second_forward_hint = ref_hint;
+            }
+        }
+    }
+
+    if (second_forward_idx < 0)
+        return;
+
+    s->cur_frame.skip_mode_frame_idx[0] =
+        AV1_REF_FRAME_LAST + FFMIN(forward_idx, second_forward_idx);
+    s->cur_frame.skip_mode_frame_idx[1] =
+        AV1_REF_FRAME_LAST + FFMAX(forward_idx, second_forward_idx);
+}
+
 static int init_tile_data(AV1DecContext *s)
 
 {
@@ -318,6 +390,9 @@ static void av1_frame_unref(AVCodecContext *avctx, AV1Frame *f)
     av_buffer_unref(&f->hwaccel_priv_buf);
     f->hwaccel_picture_private = NULL;
     f->spatial_id = f->temporal_id = 0;
+    f->order_hint = 0;
+    memset(f->skip_mode_frame_idx, 0,
+           2 * sizeof(uint8_t));
 }
 
 static int av1_frame_ref(AVCodecContext *avctx, AV1Frame *dst, const AV1Frame *src)
@@ -343,6 +418,10 @@ static int av1_frame_ref(AVCodecContext *avctx, AV1Frame *dst, const AV1Frame *s
     memcpy(dst->gm_params,
            src->gm_params,
            AV1_NUM_REF_FRAMES * 6 * sizeof(int32_t));
+    dst->order_hint = src->order_hint;
+    memcpy(dst->skip_mode_frame_idx,
+           src->skip_mode_frame_idx,
+           2 * sizeof(uint8_t));
 
     return 0;
 
@@ -613,6 +692,7 @@ static int get_current_frame(AVCodecContext *avctx)
     }
 
     global_motion_params(s);
+    skip_mode_params(s);
 
     return ret;
 }
@@ -740,6 +820,8 @@ static int av1_decode_frame(AVCodecContext *avctx, void *frame,
             s->cur_frame.spatial_id  = header->spatial_id;
             s->cur_frame.temporal_id = header->temporal_id;
 
+            s->cur_frame.order_hint = s->raw_frame_header->order_hint;
+
             if (avctx->hwaccel) {
                 ret = avctx->hwaccel->start_frame(avctx, unit->data,
                                                   unit->data_size);

libavcodec/av1dec.h

@@ -41,6 +41,9 @@ typedef struct AV1Frame {
 
     uint8_t gm_type[AV1_NUM_REF_FRAMES];
     int32_t gm_params[AV1_NUM_REF_FRAMES][6];
+
+    uint8_t order_hint;
+    uint8_t skip_mode_frame_idx[2];
 } AV1Frame;
 
 typedef struct TileGroupInfo {