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VP9 level targeting: add a new AUTO mode

In the new AUTO mode, restrict the minimum alt-ref interval and max column
tiles adaptively based on picture size, while not applying any rate control
constraints.

This mode aims to produce encodings that fit into levels corresponding to
the source picture size, with minimum compression quality lost. However, the
bitstream is not guaranteed to be level compatible, e.g., the average bitrate
may exceed level limit.

BUG=b/64451920

Change-Id: I02080b169cbbef4ab2e08c0df4697ce894aad83c

--- a/test/level_test.cc

+++ b/test/level_test.cc

@@ -130,7 +130,7 @@

     if (level == 10 || level == 11 || level == 20 || level == 21 ||

         level == 30 || level == 31 || level == 40 || level == 41 ||

         level == 50 || level == 51 || level == 52 || level == 60 ||

-        level == 61 || level == 62 || level == 0 || level == 255)

+        level == 61 || level == 62 || level == 0 || level == 1 || level == 255)

       EXPECT_EQ(VPX_CODEC_OK,

                 vpx_codec_control(&enc, VP9E_SET_TARGET_LEVEL, level));

     else

--- a/vp9/encoder/vp9_encoder.c

+++ b/vp9/encoder/vp9_encoder.c

@@ -1209,6 +1209,14 @@

         clamp(cpi->oxcf.tile_columns, min_log2_tile_cols, max_log2_tile_cols);

     cm->log2_tile_rows = cpi->oxcf.tile_rows;

   }

+

+  if (cpi->oxcf.target_level == LEVEL_AUTO) {

+    const uint32_t pic_size = cpi->common.width * cpi->common.height;

+    const int level_tile_cols = log_tile_cols_from_picsize_level(pic_size);

+    if (cm->log2_tile_cols > level_tile_cols) {

+      cm->log2_tile_cols = VPXMAX(level_tile_cols, min_log2_tile_cols);

+    }

+  }

 }

 static void update_frame_size(VP9_COMP *cpi) {

--- a/vp9/encoder/vp9_encoder.h

+++ b/vp9/encoder/vp9_encoder.h

@@ -360,6 +360,7 @@

 typedef enum {

   LEVEL_UNKNOWN = 0,

+  LEVEL_AUTO = 1,

   LEVEL_1 = 10,

   LEVEL_1_1 = 11,

   LEVEL_2 = 20,

@@ -911,6 +912,18 @@

     if (level == vp9_level_defs[i].level) return i;

   }

   return -1;

+}

+

+// Return the log2 value of max column tiles corresponding to the level that

+// the picture size fits into.

+static INLINE int log_tile_cols_from_picsize_level(uint32_t pic_size) {

+  int i;

+  for (i = LEVEL_1; i < LEVEL_MAX; ++i) {

+    if (vp9_level_defs[i].max_luma_picture_size > pic_size) {

+      return get_msb(vp9_level_defs[i].max_col_tiles);

+    }

+  }

+  return INT_MAX;

 }

 VP9_LEVEL vp9_get_level(const Vp9LevelSpec *const level_spec);

--- a/vp9/encoder/vp9_ethread.c

+++ b/vp9/encoder/vp9_ethread.c

@@ -64,6 +64,13 @@

   vp9_get_tile_n_bits(mi_cols, &min_log2_tile_cols, &max_log2_tile_cols);

   log2_tile_cols =

       clamp(cpi->oxcf.tile_columns, min_log2_tile_cols, max_log2_tile_cols);

+  if (cpi->oxcf.target_level == LEVEL_AUTO) {

+    const uint32_t pic_size = cpi->common.width * cpi->common.height;

+    const int level_tile_cols = log_tile_cols_from_picsize_level(pic_size);

+    if (log2_tile_cols > level_tile_cols) {

+      log2_tile_cols = VPXMAX(level_tile_cols, min_log2_tile_cols);

+    }

+  }

   return (1 << log2_tile_cols);

 }

--- a/vp9/encoder/vp9_ratectrl.c

+++ b/vp9/encoder/vp9_ratectrl.c

@@ -1851,6 +1851,23 @@

     // Clamp min to max

     rc->min_gf_interval = VPXMIN(rc->min_gf_interval, rc->max_gf_interval);

+

+    if (oxcf->target_level == LEVEL_AUTO) {

+      const uint32_t pic_size = cpi->common.width * cpi->common.height;

+      int i;

+      for (i = LEVEL_1; i < LEVEL_MAX; ++i) {

+        if (vp9_level_defs[i].max_luma_picture_size > pic_size) {

+          if (rc->min_gf_interval <=

+              (int)vp9_level_defs[i].min_altref_distance) {

+            rc->min_gf_interval =

+                (int)vp9_level_defs[i].min_altref_distance + 1;

+            rc->max_gf_interval =

+                VPXMAX(rc->max_gf_interval, rc->min_gf_interval);

+          }

+          break;

+        }

+      }

+    }

   }

 }

--- a/vp9/vp9_cx_iface.c

+++ b/vp9/vp9_cx_iface.c

@@ -213,7 +213,7 @@

         level != LEVEL_4 && level != LEVEL_4_1 && level != LEVEL_5 &&

         level != LEVEL_5_1 && level != LEVEL_5_2 && level != LEVEL_6 &&

         level != LEVEL_6_1 && level != LEVEL_6_2 && level != LEVEL_UNKNOWN &&

-        level != LEVEL_MAX)

+        level != LEVEL_AUTO && level != LEVEL_MAX)

       ERROR("target_level is invalid");

   }

--- a/vpxenc.c

+++ b/vpxenc.c

@@ -468,8 +468,14 @@

 static const arg_def_t target_level = ARG_DEF(

     NULL, "target-level", 1,

-    "Target level (255: off (default); 0: only keep level stats; 10: level 1.0;"

-    " 11: level 1.1; ... 62: level 6.2)");

+    "Target level\n"

+    "                                        255: off (default)\n"

+    "                                          0: only keep level stats\n"

+    "                                          1: adaptively set alt-ref "

+    "distance and column tile limit based on picture size, and keep"

+    " level stats\n"

+    "                                         10: level 1.0  11: level 1.1  "

+    "...  62: level 6.2");

 static const arg_def_t row_mt =

     ARG_DEF(NULL, "row-mt", 1,