ref: 2fa333c2ae1b6fcc1864de12a7ad344a16e2ac0a
parent: b78dad3ffad819cb79f0430ed5dc176656110b34
author: paulwilkins <paulwilkins@google.com>
date: Wed Jan 31 11:42:37 EST 2018
Improved coding on slide show content. This patch adds in detection of slide show key frame groups. The detection assumes extremely low or 0 motion for all frames in the key frame group. If this case is detected the boost level is set to a very high value and the min Q to a lower value for the key frame itself. Alt refs and golden frames are disabled to save bits (up to a limiting maximum interval currently set to 240 frames). In test samples that I created, this patch gave rise to a substantial improvement in overall psnr and a drop in data rate. In some cases the average psnr fell, however, with the boost and minQ values set as they are. This is to be expected because previously a relatively poor key frame could be followed by progressively better alt refs. For example a key frame at q7.5 but subsequent alt refs improving it to lossless. Given that average psnr tends to be dominated by the best frames, a ramp like this from q7.5 to lossless may give a better average psnr than, for example, coding the entire sequence at q2.5. Overall psnr, however, will be much better in the latter case. The option exists to boost the key frame further which would insure much better results for all metrics, but at the expense of smaller bitrate savings. Given that these samples tend to have very good quality anyway this seems like a bad trade off. For slides displayed for several seconds, bitrate savings of >= 20% are likely and much larger gains are possible in some cases. Change-Id: Ib4b61e153c55d3f2f561153da13fdb56f397a52b
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -2281,7 +2281,8 @@
// Define middle frame
mid_frame_idx = frame_index + (rc->baseline_gf_interval >> 1) - 1;
- normal_frames = (rc->baseline_gf_interval - rc->source_alt_ref_pending);
+ normal_frames =
+ rc->baseline_gf_interval - (key_frame || rc->source_alt_ref_pending);
if (normal_frames > 1)
normal_frame_bits = (int)(total_group_bits / normal_frames);
else
@@ -2547,9 +2548,9 @@
}
// Break out conditions.
- if (
- // Break at active_max_gf_interval unless almost totally static.
- ((i >= active_max_gf_interval) && (zero_motion_accumulator < 0.995)) ||
+ // Break at maximum of active_max_gf_interval unless almost totally static.
+ if (((twopass->kf_zeromotion_pct < STATIC_KF_GROUP_THRESH) &&
+ (i >= active_max_gf_interval) && (zero_motion_accumulator < 0.995)) ||
(
// Don't break out with a very short interval.
(i >= active_min_gf_interval) &&
@@ -2569,8 +2570,8 @@
rc->constrained_gf_group = (i >= rc->frames_to_key) ? 1 : 0;
// Should we use the alternate reference frame.
- if (allow_alt_ref && (i < cpi->oxcf.lag_in_frames) &&
- (i >= rc->min_gf_interval)) {+ if ((twopass->kf_zeromotion_pct < STATIC_KF_GROUP_THRESH) && allow_alt_ref &&
+ (i < cpi->oxcf.lag_in_frames) && (i >= rc->min_gf_interval)) {const int forward_frames = (rc->frames_to_key - i >= i - 1)
? i - 1
: VPXMAX(0, rc->frames_to_key - i);
@@ -2598,7 +2599,10 @@
#endif
// Set the interval until the next gf.
- rc->baseline_gf_interval = i - (is_key_frame || rc->source_alt_ref_pending);
+ rc->baseline_gf_interval =
+ (twopass->kf_zeromotion_pct < STATIC_KF_GROUP_THRESH)
+ ? (i - (is_key_frame || rc->source_alt_ref_pending))
+ : i;
// Only encode alt reference frame in temporal base layer. So
// baseline_gf_interval should be multiple of a temporal layer group
@@ -3025,8 +3029,14 @@
double zm_factor;
// Monitor for static sections.
- zero_motion_accumulator = VPXMIN(
- zero_motion_accumulator, get_zero_motion_factor(cpi, &next_frame));
+ // First frame in kf group the second ref indicator is invalid.
+ if (i > 0) {+ zero_motion_accumulator = VPXMIN(
+ zero_motion_accumulator, get_zero_motion_factor(cpi, &next_frame));
+ } else {+ zero_motion_accumulator =
+ next_frame.pcnt_inter - next_frame.pcnt_motion;
+ }
// Factor 0.75-1.25 based on how much of frame is static.
zm_factor = (0.75 + (zero_motion_accumulator / 2.0));
@@ -3062,10 +3072,16 @@
twopass->section_intra_rating = calculate_section_intra_ratio(
start_position, twopass->stats_in_end, rc->frames_to_key);
- // Apply various clamps for min and max boost
- rc->kf_boost = VPXMAX((int)boost_score, (rc->frames_to_key * 3));
- rc->kf_boost = VPXMAX(rc->kf_boost, MIN_KF_TOT_BOOST);
- rc->kf_boost = VPXMIN(rc->kf_boost, MAX_KF_TOT_BOOST);
+ // Special case for static / slide show content but dont apply
+ // if the kf group is very short.
+ if ((zero_motion_accumulator > 0.99) && (rc->frames_to_key > 8)) {+ rc->kf_boost = VPXMAX((rc->frames_to_key * 100), MAX_KF_TOT_BOOST);
+ } else {+ // Apply various clamps for min and max boost
+ rc->kf_boost = VPXMAX((int)boost_score, (rc->frames_to_key * 3));
+ rc->kf_boost = VPXMAX(rc->kf_boost, MIN_KF_TOT_BOOST);
+ rc->kf_boost = VPXMIN(rc->kf_boost, MAX_KF_TOT_BOOST);
+ }
// Work out how many bits to allocate for the key frame itself.
kf_bits = calculate_boost_bits((rc->frames_to_key - 1), rc->kf_boost,
--- a/vp9/encoder/vp9_firstpass.h
+++ b/vp9/encoder/vp9_firstpass.h
@@ -120,12 +120,12 @@
typedef struct {unsigned char index;
unsigned char first_inter_index;
- RATE_FACTOR_LEVEL rf_level[(MAX_LAG_BUFFERS * 2) + 1];
- FRAME_UPDATE_TYPE update_type[(MAX_LAG_BUFFERS * 2) + 1];
- unsigned char arf_src_offset[(MAX_LAG_BUFFERS * 2) + 1];
- unsigned char arf_update_idx[(MAX_LAG_BUFFERS * 2) + 1];
- unsigned char arf_ref_idx[(MAX_LAG_BUFFERS * 2) + 1];
- int bit_allocation[(MAX_LAG_BUFFERS * 2) + 1];
+ RATE_FACTOR_LEVEL rf_level[MAX_STATIC_GF_GROUP_LENGTH + 1];
+ FRAME_UPDATE_TYPE update_type[MAX_STATIC_GF_GROUP_LENGTH + 1];
+ unsigned char arf_src_offset[MAX_STATIC_GF_GROUP_LENGTH + 1];
+ unsigned char arf_update_idx[MAX_STATIC_GF_GROUP_LENGTH + 1];
+ unsigned char arf_ref_idx[MAX_STATIC_GF_GROUP_LENGTH + 1];
+ int bit_allocation[MAX_STATIC_GF_GROUP_LENGTH + 1];
} GF_GROUP;
typedef struct {--- a/vp9/encoder/vp9_ratectrl.c
+++ b/vp9/encoder/vp9_ratectrl.c
@@ -1103,6 +1103,9 @@
// Baseline value derived from cpi->active_worst_quality and kf boost.
active_best_quality =
get_kf_active_quality(rc, active_worst_quality, cm->bit_depth);
+ if (cpi->twopass.kf_zeromotion_pct >= STATIC_KF_GROUP_THRESH) {+ active_best_quality /= 4;
+ }
// Allow somewhat lower kf minq with small image formats.
if ((cm->width * cm->height) <= (352 * 288)) {@@ -1866,13 +1869,8 @@
rc->max_gf_interval = vp9_rc_get_default_max_gf_interval(
cpi->framerate, rc->min_gf_interval);
- // Extended interval for genuinely static scenes
- rc->static_scene_max_gf_interval = MAX_LAG_BUFFERS * 2;
-
- if (is_altref_enabled(cpi)) {- if (rc->static_scene_max_gf_interval > oxcf->lag_in_frames - 1)
- rc->static_scene_max_gf_interval = oxcf->lag_in_frames - 1;
- }
+ // Extended max interval for genuinely static scenes like slide shows.
+ rc->static_scene_max_gf_interval = MAX_STATIC_GF_GROUP_LENGTH;
if (rc->max_gf_interval > rc->static_scene_max_gf_interval)
rc->max_gf_interval = rc->static_scene_max_gf_interval;
--- a/vp9/encoder/vp9_ratectrl.h
+++ b/vp9/encoder/vp9_ratectrl.h
@@ -34,6 +34,14 @@
#define FRAME_OVERHEAD_BITS 200
+// Threshold used to define a KF group as static (e.g. a slide show).
+// Essentially this means that no frame in the group has more than 1% of MBs
+// that are not marked as coded with 0,0 motion in the first pass.
+#define STATIC_KF_GROUP_THRESH 99
+
+// The maximum duration of a GF group that is static (for example a slide show).
+#define MAX_STATIC_GF_GROUP_LENGTH 250
+
typedef enum {INTER_NORMAL = 0,
INTER_HIGH = 1,