Enable low-latency (uni-directional) compound mode (normative)

Change-Id: Ie9cb6bb66c35eecd173532b3111b98a2aaf0d913

av1/common/pred_common.c

@@ -278,19 +278,29 @@ int av1_get_reference_mode_context(const AV1_COMMON *cm,
 //
 // NOTE(zoeliu): The probability of ref_frame[0] is either
 //               GOLDEN_FRAME or LAST3_FRAME.
+#if CONFIG_LOWDELAY_COMPOUND
+int av1_get_pred_context_comp_ref_p(UNUSED const AV1_COMMON *cm,
+                                    const MACROBLOCKD *xd) {
+#else
 int av1_get_pred_context_comp_ref_p(const AV1_COMMON *cm,
                                     const MACROBLOCKD *xd) {
+#endif
   int pred_context;
   const MB_MODE_INFO *const above_mbmi = xd->above_mbmi;
   const MB_MODE_INFO *const left_mbmi = xd->left_mbmi;
   const int above_in_image = xd->up_available;
   const int left_in_image = xd->left_available;
 
-  // Note:
-  // The mode info data structure has a one element border above and to the
-  // left of the entries correpsonding to real macroblocks.
-  // The prediction flags in these dummy entries are initialised to 0.
+// Note:
+// The mode info data structure has a one element border above and to the
+// left of the entries correpsonding to real macroblocks.
+// The prediction flags in these dummy entries are initialised to 0.
+#if CONFIG_LOWDELAY_COMPOUND  // No change to bitstream
+  // Code seems to assume that signbias of cm->comp_bwd_ref[0] is always 1
+  const int bwd_ref_sign_idx = 1;
+#else
   const int bwd_ref_sign_idx = cm->ref_frame_sign_bias[cm->comp_bwd_ref[0]];
+#endif
   const int fwd_ref_sign_idx = !bwd_ref_sign_idx;
 
   if (above_in_image && left_in_image) {  // both edges available
@@ -378,19 +388,29 @@ int av1_get_pred_context_comp_ref_p(const AV1_COMMON *cm,
 //
 // NOTE(zoeliu): The probability of ref_frame[0] is LAST_FRAME,
 // conditioning on it is either LAST_FRAME or LAST2_FRAME.
+#if CONFIG_LOWDELAY_COMPOUND
+int av1_get_pred_context_comp_ref_p1(UNUSED const AV1_COMMON *cm,
+                                     const MACROBLOCKD *xd) {
+#else
 int av1_get_pred_context_comp_ref_p1(const AV1_COMMON *cm,
                                      const MACROBLOCKD *xd) {
+#endif
   int pred_context;
   const MB_MODE_INFO *const above_mbmi = xd->above_mbmi;
   const MB_MODE_INFO *const left_mbmi = xd->left_mbmi;
   const int above_in_image = xd->up_available;
   const int left_in_image = xd->left_available;
 
-  // Note:
-  // The mode info data structure has a one element border above and to the
-  // left of the entries correpsonding to real macroblocks.
-  // The prediction flags in these dummy entries are initialised to 0.
+// Note:
+// The mode info data structure has a one element border above and to the
+// left of the entries correpsonding to real macroblocks.
+// The prediction flags in these dummy entries are initialised to 0.
+#if CONFIG_LOWDELAY_COMPOUND  // No change to bitstream
+  // Code seems to assume that signbias of cm->comp_bwd_ref[0] is always 1
+  const int bwd_ref_sign_idx = 1;
+#else
   const int bwd_ref_sign_idx = cm->ref_frame_sign_bias[cm->comp_bwd_ref[0]];
+#endif
   const int fwd_ref_sign_idx = !bwd_ref_sign_idx;
 
   if (above_in_image && left_in_image) {  // both edges available
@@ -479,19 +499,29 @@ int av1_get_pred_context_comp_ref_p1(const AV1_COMMON *cm,
 //
 // NOTE(zoeliu): The probability of ref_frame[0] is GOLDEN_FRAME,
 // conditioning on it is either GOLDEN or LAST3.
+#if CONFIG_LOWDELAY_COMPOUND
+int av1_get_pred_context_comp_ref_p2(UNUSED const AV1_COMMON *cm,
+                                     const MACROBLOCKD *xd) {
+#else
 int av1_get_pred_context_comp_ref_p2(const AV1_COMMON *cm,
                                      const MACROBLOCKD *xd) {
+#endif
   int pred_context;
   const MB_MODE_INFO *const above_mbmi = xd->above_mbmi;
   const MB_MODE_INFO *const left_mbmi = xd->left_mbmi;
   const int above_in_image = xd->up_available;
   const int left_in_image = xd->left_available;
 
-  // Note:
-  // The mode info data structure has a one element border above and to the
-  // left of the entries correpsonding to real macroblocks.
-  // The prediction flags in these dummy entries are initialised to 0.
+// Note:
+// The mode info data structure has a one element border above and to the
+// left of the entries correpsonding to real macroblocks.
+// The prediction flags in these dummy entries are initialised to 0.
+#if CONFIG_LOWDELAY_COMPOUND  // No change to bitstream
+  // Code seems to assume that signbias of cm->comp_bwd_ref[0] is always 1
+  const int bwd_ref_sign_idx = 1;
+#else
   const int bwd_ref_sign_idx = cm->ref_frame_sign_bias[cm->comp_bwd_ref[0]];
+#endif
   const int fwd_ref_sign_idx = !bwd_ref_sign_idx;
 
   if (above_in_image && left_in_image) {  // both edges available
@@ -574,19 +604,29 @@ int av1_get_pred_context_comp_ref_p2(const AV1_COMMON *cm,
 }
 
 // Returns a context number for the given MB prediction signal
+#if CONFIG_LOWDELAY_COMPOUND
+int av1_get_pred_context_comp_bwdref_p(UNUSED const AV1_COMMON *cm,
+                                       const MACROBLOCKD *xd) {
+#else
 int av1_get_pred_context_comp_bwdref_p(const AV1_COMMON *cm,
                                        const MACROBLOCKD *xd) {
+#endif
   int pred_context;
   const MB_MODE_INFO *const above_mbmi = xd->above_mbmi;
   const MB_MODE_INFO *const left_mbmi = xd->left_mbmi;
   const int above_in_image = xd->up_available;
   const int left_in_image = xd->left_available;
 
-  // Note:
-  // The mode info data structure has a one element border above and to the
-  // left of the entries corresponding to real macroblocks.
-  // The prediction flags in these dummy entries are initialized to 0.
+// Note:
+// The mode info data structure has a one element border above and to the
+// left of the entries corresponding to real macroblocks.
+// The prediction flags in these dummy entries are initialized to 0.
+#if CONFIG_LOWDELAY_COMPOUND  // No change to bitstream
+  // Code seems to assume that signbias of cm->comp_bwd_ref[0] is always 1
+  const int bwd_ref_sign_idx = 1;
+#else
   const int bwd_ref_sign_idx = cm->ref_frame_sign_bias[cm->comp_bwd_ref[0]];
+#endif
   const int fwd_ref_sign_idx = !bwd_ref_sign_idx;
 
   if (above_in_image && left_in_image) {  // both edges available

av1/decoder/decodeframe.c

@@ -92,12 +92,16 @@ static size_t read_uncompressed_header(AV1Decoder *pbi,
                                        struct aom_read_bit_buffer *rb);
 
 static int is_compound_reference_allowed(const AV1_COMMON *cm) {
+#if CONFIG_LOWDELAY_COMPOUND  // Normative in decoder
+  return !frame_is_intra_only(cm);
+#else
   int i;
   if (frame_is_intra_only(cm)) return 0;
   for (i = 1; i < INTER_REFS_PER_FRAME; ++i)
     if (cm->ref_frame_sign_bias[i + 1] != cm->ref_frame_sign_bias[1]) return 1;
 
   return 0;
+#endif
 }
 
 static void setup_compound_reference_mode(AV1_COMMON *cm) {

av1/decoder/decodemv.c

@@ -1238,11 +1238,15 @@ static void read_ref_frames(AV1_COMMON *const cm, MACROBLOCKD *const xd,
     const REFERENCE_MODE mode = read_block_reference_mode(cm, xd, r);
     // FIXME(rbultje) I'm pretty sure this breaks segmentation ref frame coding
     if (mode == COMPOUND_REFERENCE) {
+#if CONFIG_LOWDELAY_COMPOUND  // Normative in decoder (for low delay)
+      const int idx = 1;
+#else
 #if CONFIG_EXT_REFS
       const int idx = cm->ref_frame_sign_bias[cm->comp_bwd_ref[0]];
 #else
       const int idx = cm->ref_frame_sign_bias[cm->comp_fixed_ref];
 #endif  // CONFIG_EXT_REFS
+#endif
       const int ctx = av1_get_pred_context_comp_ref_p(cm, xd);
 
       const int bit = aom_read(r, fc->comp_ref_prob[ctx][0], ACCT_STR);

av1/encoder/encodeframe.c

@@ -5428,6 +5428,21 @@ void av1_encode_frame(AV1_COMP *cpi) {
   // side behavior is where the ALT ref buffer has opposite sign bias to
   // the other two.
   if (!frame_is_intra_only(cm)) {
+#if CONFIG_LOWDELAY_COMPOUND  // Normative in encoder
+    cpi->allow_comp_inter_inter = 1;
+#if CONFIG_EXT_REFS
+    cm->comp_fwd_ref[0] = LAST_FRAME;
+    cm->comp_fwd_ref[1] = LAST2_FRAME;
+    cm->comp_fwd_ref[2] = LAST3_FRAME;
+    cm->comp_fwd_ref[3] = GOLDEN_FRAME;
+    cm->comp_bwd_ref[0] = BWDREF_FRAME;
+    cm->comp_bwd_ref[1] = ALTREF_FRAME;
+#else
+    cm->comp_fixed_ref = ALTREF_FRAME;
+    cm->comp_var_ref[0] = LAST_FRAME;
+    cm->comp_var_ref[1] = GOLDEN_FRAME;
+#endif  // CONFIG_EXT_REFS
+#else
     if ((cm->ref_frame_sign_bias[ALTREF_FRAME] ==
          cm->ref_frame_sign_bias[GOLDEN_FRAME]) ||
         (cm->ref_frame_sign_bias[ALTREF_FRAME] ==
@@ -5449,6 +5464,7 @@ void av1_encode_frame(AV1_COMP *cpi) {
       cm->comp_var_ref[1] = GOLDEN_FRAME;
 #endif  // CONFIG_EXT_REFS
     }
+#endif
   } else {
     cpi->allow_comp_inter_inter = 0;
   }

configure

@@ -323,6 +323,7 @@ EXPERIMENT_LIST="
     new_multisymbol
     compound_singleref
     aom_qm
+    lowdelay_compound
 "
 CONFIG_LIST="
     dependency_tracking