ref: e458ca3d52dbe9bf79ee31c712e3d87e751c5307
parent: 3a0d78272f4a10835f9b2881405e1e62f0344335
author: Paul Wilkins <paulwilkins@google.com>
date: Wed Mar 13 12:20:23 EDT 2019
Improve key frame detection Improve detection of key frames especially in low contrast and low motion regions. This patch adds a function to the key frame detection to test for specific patterns in the intra signal in the first pass stats that tend to be indicative of a key frame. This is intended to compliment the existing code and finds some scene cuts that were previously being misssed. Tested on two clips where the existing code was struggling to identify the key frames this patch improved detection as follows. Film clip 1: (detected / actual) Old (2/5) New (5/5) Film Clip 2 Old 4/11 and one false +, New 7/11 and 1 false +. Short 4K Film Scene Old 1/2 New 2/2 In testing so far I have not seen many extra false +'s though it is likely that there will be some cases and this may need further tweaking. One one of our longer form film test reels ~20k frames) the change picked up around 35 key frames that were previously missed, mainly in darker scenes. There were a few extra (or different) false positives cause by bright flashes or explosions but these were cases where there was little difference between inter and intra coding. Awaiting testing on standard sets. Change-Id: I1ff4a587e0a47667eb93b197f39b79a1130faeca
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -2746,11 +2746,54 @@
(this_frame->coded_error > (next_frame->coded_error * ERROR_SPIKE));
}
+// This test looks for anomalous changes in the nature of the intra signal
+// related to the previous and next frame as an indicator for coding a key
+// frame. This test serves to detect some additional scene cuts,
+// especially in lowish motion and low contrast sections, that are missed
+// by the other tests.
+static int intra_step_transition(const FIRSTPASS_STATS *this_frame,
+ const FIRSTPASS_STATS *last_frame,
+ const FIRSTPASS_STATS *next_frame) {+ double last_ii_ratio;
+ double this_ii_ratio;
+ double next_ii_ratio;
+ double last_pcnt_intra = 1.0 - last_frame->pcnt_inter;
+ double this_pcnt_intra = 1.0 - this_frame->pcnt_inter;
+ double next_pcnt_intra = 1.0 - next_frame->pcnt_inter;
+ double mod_this_intra = this_pcnt_intra + this_frame->pcnt_neutral;
+
+ // Calculate ii ratio for this frame last frame and next frame.
+ last_ii_ratio =
+ last_frame->intra_error / DOUBLE_DIVIDE_CHECK(last_frame->coded_error);
+ this_ii_ratio =
+ this_frame->intra_error / DOUBLE_DIVIDE_CHECK(this_frame->coded_error);
+ next_ii_ratio =
+ next_frame->intra_error / DOUBLE_DIVIDE_CHECK(next_frame->coded_error);
+
+ // Return true the intra/inter ratio for the current frame is
+ // low but better in the next and previous frame and the relative useage of
+ // intra in the current frame is markedly higher than the last and next frame.
+ if ((this_ii_ratio < 2.0) && (last_ii_ratio > 2.25) &&
+ (next_ii_ratio > 2.25) && (this_pcnt_intra > (3 * last_pcnt_intra)) &&
+ (this_pcnt_intra > (3 * next_pcnt_intra)) &&
+ ((this_pcnt_intra > 0.075) || (mod_this_intra > 0.85))) {+ return 1;
+ // Very low inter intra ratio (i.e. not much gain from inter coding), most
+ // blocks neutral on coding method and better inter prediction either side
+ } else if ((this_ii_ratio < 1.25) && (mod_this_intra > 0.85) &&
+ (this_ii_ratio < last_ii_ratio * 0.9) &&
+ (this_ii_ratio < next_ii_ratio * 0.9)) {+ return 1;
+ } else {+ return 0;
+ }
+}
+
// Minimum % intra coding observed in first pass (1.0 = 100%)
#define MIN_INTRA_LEVEL 0.25
// Threshold for use of the lagging second reference frame. Scene cuts do not
// usually have a high second ref useage.
-#define SECOND_REF_USEAGE_THRESH 0.125
+#define SECOND_REF_USEAGE_THRESH 0.2
// Hard threshold where the first pass chooses intra for almost all blocks.
// In such a case even if the frame is not a scene cut coding a key frame
// may be a good option.
@@ -2777,8 +2820,9 @@
(this_frame->pcnt_second_ref < SECOND_REF_USEAGE_THRESH) &&
((this_frame->pcnt_inter < VERY_LOW_INTER_THRESH) ||
(slide_transition(this_frame, last_frame, next_frame)) ||
- (((this_frame->coded_error > (next_frame->coded_error * 1.1)) &&
- (this_frame->coded_error > (last_frame->coded_error * 1.1))) &&
+ (intra_step_transition(this_frame, last_frame, next_frame)) ||
+ (((this_frame->coded_error > (next_frame->coded_error * 1.2)) &&
+ (this_frame->coded_error > (last_frame->coded_error * 1.2))) &&
(pcnt_intra > MIN_INTRA_LEVEL) &&
((pcnt_intra + this_frame->pcnt_neutral) > 0.5) &&
((this_frame->intra_error /