Expose params min-gf-interval/max-gf-interval

Adds two new vp9 parameters --min-gf-interval and --max-gf-interval
to enable testing based on frequency of alt-ref frames.

Also adds a unit-test to test enforcement of min-gf-interval.

For both these parameters the default value is 0, which indicates
they are picked by the encoder, based on resolution and framerate
considerations. If they are greater than zero, the specified
parameter is honored.

(Additional note by paulwilkins)
Note that there is a slight oddity in that key frames are also GFs and
considered part of  GF only group. However they are treated as not
being part of an arf group because for arf groups the previous GF is
assumed to be the terminal or overlay frame for the previous group.

(end note)

Change-Id: Ibf0c30b72074b3f71918ab278ccccc02a95a70a0

5 files changed, 67 insertions, 22 deletions

diff --git a/vp9/encoder/vp9_encoder.c b/vp9/encoder/vp9_encoder.c
index b9b11064d..ac68b6c16 100644
--- a/vp9/encoder/vp9_encoder.c
+++ b/vp9/encoder/vp9_encoder.c
@@ -1467,7 +1467,7 @@ void vp9_change_config(struct VP9_COMP *cpi, const VP9EncoderConfig *oxcf) {
   cpi->td.mb.e_mbd.bd = (int)cm->bit_depth;
 #endif  // CONFIG_VP9_HIGHBITDEPTH
 
-  rc->baseline_gf_interval = DEFAULT_GF_INTERVAL;
+  rc->baseline_gf_interval = (MIN_GF_INTERVAL + MAX_GF_INTERVAL) / 2;
 
   cpi->refresh_golden_frame = 0;
   cpi->refresh_last_frame = 1;
diff --git a/vp9/encoder/vp9_encoder.h b/vp9/encoder/vp9_encoder.h
index cd7a5dc92..10ad2d391 100644
--- a/vp9/encoder/vp9_encoder.h
+++ b/vp9/encoder/vp9_encoder.h
@@ -50,8 +50,6 @@
 extern "C" {
 #endif
 
-#define DEFAULT_GF_INTERVAL         10
-
 typedef struct {
   int nmvjointcost[MV_JOINTS];
   int nmvcosts[2][MV_VALS];
@@ -219,6 +217,9 @@ typedef struct VP9EncoderConfig {
   int arnr_max_frames;
   int arnr_strength;
 
+  int min_gf_interval;
+  int max_gf_interval;
+
   int tile_columns;
   int tile_rows;
 
diff --git a/vp9/encoder/vp9_firstpass.c b/vp9/encoder/vp9_firstpass.c
index 16640fed9..b195c4a16 100644
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -1851,7 +1851,8 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
   int64_t gf_group_bits;
   double gf_group_error_left;
   int gf_arf_bits;
-  int is_key_frame = frame_is_intra_only(cm);
+  const int is_key_frame = frame_is_intra_only(cm);
+  const int kf_or_arf_active = is_key_frame || rc->source_alt_ref_active;
 
   // Reset the GF group data structures unless this is a key
   // frame in which case it will already have been done.
@@ -1904,7 +1905,10 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
       // bits to spare and are better with a smaller interval and smaller boost.
       // At high Q when there are few bits to spare we are better with a longer
       // interval to spread the cost of the GF.
-      active_max_gf_interval = 12 + MIN(4, (int_lbq / 6));
+      active_max_gf_interval = rc->max_gf_interval - 4 + MIN(4, (int_lbq / 6));
+      if (active_max_gf_interval < active_min_gf_interval)
+        active_max_gf_interval = active_min_gf_interval;
+
       if (active_max_gf_interval > rc->max_gf_interval)
         active_max_gf_interval = rc->max_gf_interval;
       if (active_max_gf_interval < active_min_gf_interval)
@@ -1966,10 +1970,11 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
     // Break out conditions.
     if (
       // Break at active_max_gf_interval unless almost totally static.
-      (i >= active_max_gf_interval && (zero_motion_accumulator < 0.995)) ||
+      ((i >= active_max_gf_interval + kf_or_arf_active) &&
+       (zero_motion_accumulator < 0.995)) ||
       (
         // Don't break out with a very short interval.
-        (i > active_min_gf_interval) &&
+        (i >= active_min_gf_interval + kf_or_arf_active) &&
         (!flash_detected) &&
         ((mv_ratio_accumulator > mv_ratio_accumulator_thresh) ||
          (abs_mv_in_out_accumulator > 3.0) ||
diff --git a/vp9/encoder/vp9_ratectrl.c b/vp9/encoder/vp9_ratectrl.c
index 85003f65e..be09bca0c 100644
--- a/vp9/encoder/vp9_ratectrl.c
+++ b/vp9/encoder/vp9_ratectrl.c
@@ -276,6 +276,27 @@ static void update_buffer_level(VP9_COMP *cpi, int encoded_frame_size) {
   }
 }
 
+int vp9_rc_get_default_min_gf_interval(
+    int width, int height, double framerate) {
+  // Assume we do not need any constraint lower than 4K 20 fps
+  static const double factor_safe = 3840 * 2160 * 20.0;
+  const double factor = width * height * framerate;
+
+  if (factor <= factor_safe)
+    return MIN_GF_INTERVAL;
+  else
+    return (int)(MIN_GF_INTERVAL * factor / factor_safe + 0.5);
+  // Note this logic makes:
+  // 4K24: 5
+  // 4K30: 6
+  // 4K60: 12
+}
+
+int vp9_rc_get_default_max_gf_interval(double framerate, int min_gf_interval) {
+  int interval = MIN(MAX_GF_INTERVAL, (int)(framerate * 0.75));
+  return MAX(interval, min_gf_interval);
+}
+
 void vp9_rc_init(const VP9EncoderConfig *oxcf, int pass, RATE_CONTROL *rc) {
   int i;
 
@@ -284,9 +305,9 @@ void vp9_rc_init(const VP9EncoderConfig *oxcf, int pass, RATE_CONTROL *rc) {
     rc->avg_frame_qindex[INTER_FRAME] = oxcf->worst_allowed_q;
   } else {
     rc->avg_frame_qindex[KEY_FRAME] = (oxcf->worst_allowed_q +
-                                           oxcf->best_allowed_q) / 2;
+                                       oxcf->best_allowed_q) / 2;
     rc->avg_frame_qindex[INTER_FRAME] = (oxcf->worst_allowed_q +
-                                           oxcf->best_allowed_q) / 2;
+                                         oxcf->best_allowed_q) / 2;
   }
 
   rc->last_q[KEY_FRAME] = oxcf->best_allowed_q;
@@ -304,7 +325,6 @@ void vp9_rc_init(const VP9EncoderConfig *oxcf, int pass, RATE_CONTROL *rc) {
   rc->total_target_bits = 0;
   rc->total_target_vs_actual = 0;
 
-  rc->baseline_gf_interval = DEFAULT_GF_INTERVAL;
   rc->frames_since_key = 8;  // Sensible default for first frame.
   rc->this_key_frame_forced = 0;
   rc->next_key_frame_forced = 0;
@@ -322,6 +342,16 @@ void vp9_rc_init(const VP9EncoderConfig *oxcf, int pass, RATE_CONTROL *rc) {
   for (i = 0; i < RATE_FACTOR_LEVELS; ++i) {
     rc->rate_correction_factors[i] = 1.0;
   }
+
+  rc->min_gf_interval = oxcf->min_gf_interval;
+  rc->max_gf_interval = oxcf->max_gf_interval;
+  if (rc->min_gf_interval == 0)
+    rc->min_gf_interval = vp9_rc_get_default_min_gf_interval(
+        oxcf->width, oxcf->height, oxcf->init_framerate);
+  if (rc->max_gf_interval == 0)
+    rc->max_gf_interval = vp9_rc_get_default_max_gf_interval(
+        oxcf->init_framerate, rc->min_gf_interval);
+  rc->baseline_gf_interval = (rc->min_gf_interval + rc->max_gf_interval) / 2;
 }
 
 int vp9_rc_drop_frame(VP9_COMP *cpi) {
@@ -1382,7 +1412,7 @@ void vp9_rc_get_one_pass_vbr_params(VP9_COMP *cpi) {
     cm->frame_type = INTER_FRAME;
   }
   if (rc->frames_till_gf_update_due == 0) {
-    rc->baseline_gf_interval = DEFAULT_GF_INTERVAL;
+    rc->baseline_gf_interval = (rc->min_gf_interval + rc->max_gf_interval) / 2;
     rc->frames_till_gf_update_due = rc->baseline_gf_interval;
     // NOTE: frames_till_gf_update_due must be <= frames_to_key.
     if (rc->frames_till_gf_update_due > rc->frames_to_key) {
@@ -1576,7 +1606,8 @@ void vp9_rc_get_one_pass_cbr_params(VP9_COMP *cpi) {
     if (cpi->oxcf.aq_mode == CYCLIC_REFRESH_AQ)
       vp9_cyclic_refresh_set_golden_update(cpi);
     else
-      rc->baseline_gf_interval = DEFAULT_GF_INTERVAL;
+      rc->baseline_gf_interval =
+          (rc->min_gf_interval + rc->max_gf_interval) / 2;
     rc->frames_till_gf_update_due = rc->baseline_gf_interval;
     // NOTE: frames_till_gf_update_due must be <= frames_to_key.
     if (rc->frames_till_gf_update_due > rc->frames_to_key)
@@ -1649,20 +1680,19 @@ int vp9_compute_qdelta_by_rate(const RATE_CONTROL *rc, FRAME_TYPE frame_type,
   return target_index - qindex;
 }
 
-#define MIN_GF_INTERVAL     4
-#define MAX_GF_INTERVAL     16
 void vp9_rc_set_gf_interval_range(const VP9_COMP *const cpi,
                                   RATE_CONTROL *const rc) {
   const VP9EncoderConfig *const oxcf = &cpi->oxcf;
 
-  // Set a minimum interval.
-  rc->min_gf_interval =
-    MIN(MAX_GF_INTERVAL, MAX(MIN_GF_INTERVAL, (int)(cpi->framerate * 0.125)));
-
-  // Set Maximum gf/arf interval.
-  rc->max_gf_interval =
-    MIN(MAX_GF_INTERVAL, (int)(cpi->framerate * 0.75));
-  // Round up to next even number if odd.
+  // Set Maximum gf/arf interval
+  rc->max_gf_interval = oxcf->max_gf_interval;
+  rc->min_gf_interval = oxcf->min_gf_interval;
+  if (rc->min_gf_interval == 0)
+    rc->min_gf_interval = vp9_rc_get_default_min_gf_interval(
+        oxcf->width, oxcf->height, cpi->framerate);
+  if (rc->max_gf_interval == 0)
+    rc->max_gf_interval = vp9_rc_get_default_max_gf_interval(
+        cpi->framerate, rc->min_gf_interval);
   rc->max_gf_interval += (rc->max_gf_interval & 0x01);
 
   // Extended interval for genuinely static scenes
diff --git a/vp9/encoder/vp9_ratectrl.h b/vp9/encoder/vp9_ratectrl.h
index a10836c74..f9b0488bb 100644
--- a/vp9/encoder/vp9_ratectrl.h
+++ b/vp9/encoder/vp9_ratectrl.h
@@ -24,6 +24,9 @@ extern "C" {
 // Bits Per MB at different Q (Multiplied by 512)
 #define BPER_MB_NORMBITS    9
 
+#define MIN_GF_INTERVAL     4
+#define MAX_GF_INTERVAL     16
+
 typedef enum {
   INTER_NORMAL = 0,
   INTER_HIGH = 1,
@@ -155,6 +158,12 @@ double vp9_convert_qindex_to_q(int qindex, vpx_bit_depth_t bit_depth);
 
 void vp9_rc_init_minq_luts(void);
 
+int vp9_rc_get_default_min_gf_interval(int width, int height, double framerate);
+// Note vp9_rc_get_default_max_gf_interval() requires the min_gf_interval to
+// be passed in to ensure that the max_gf_interval returned is at least as bis
+// as that.
+int vp9_rc_get_default_max_gf_interval(double framerate, int min_frame_rate);
+
 // Generally at the high level, the following flow is expected
 // to be enforced for rate control:
 // First call per frame, one of: