ref: 3af3593c8ecb2a724c3c9f63e2186366550854fa
parent: 431dac08d10b28803a0b5754337099bc79a79fb5
author: Paul Wilkins <paulwilkins@google.com>
date: Fri Jan 7 11:33:59 EST 2011
Limit Q variability in two pass. In two pass encoding each frame is given an active Q range to work with. This change limits how much this Q range can be altered over time from the initial estimate made for the clip as a whole. There is some danger this could lead to overshoot or undershoot in some corner cases but it helps considerably in regard to clips where either there is a glut or famine of bits in some sections, particularly near the end of a clip. Change-Id: I34fcd1af31d2ee3d5444f93e334645254043026e
--- a/vp8/encoder/firstpass.c
+++ b/vp8/encoder/firstpass.c
@@ -66,7 +66,6 @@
static int vscale_lookup[7] = {0, 1, 1, 2, 2, 3, 3}; static int hscale_lookup[7] = {0, 0, 1, 1, 2, 2, 3};-
void vp8_find_next_key_frame(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame);
int vp8_input_stats(VP8_COMP *cpi, FIRSTPASS_STATS *fps);
@@ -907,7 +906,7 @@
double pow_lowq = 0.40;
if (section_target_bandwitdh <= 0)
- return MAXQ;
+ return cpi->maxq_max_limit; // Highest value allowed
target_norm_bits_per_mb = (section_target_bandwitdh < (1 << 20)) ? (512 * section_target_bandwitdh) / num_mbs : 512 * (section_target_bandwitdh / num_mbs);
@@ -943,10 +942,12 @@
// Correction factor used for Q values >= 20
corr_high = pow(err_per_mb / BASE_ERRPERMB, pow_highq);
- corr_high = (corr_high < 0.05) ? 0.05 : (corr_high > 5.0) ? 5.0 : corr_high;
+ corr_high = (corr_high < 0.05)
+ ? 0.05 : (corr_high > 5.0) ? 5.0 : corr_high;
- // Try and pick a Q that should be high enough to encode the content at the given rate.
- for (Q = 0; Q < MAXQ; Q++)
+ // Try and pick a Q that should be high enough to encode the
+ // content at the given rate.
+ for (Q = cpi->maxq_min_limit; Q < cpi->maxq_max_limit; Q++)
{int bits_per_mb_at_this_q;
@@ -1993,20 +1994,29 @@
if (cpi->common.current_video_frame == 0)
{- // guess at 2nd pass q
+ // guess at 2nd pass max q
cpi->est_max_qcorrection_factor = 1.0;
- tmp_q = estimate_max_q(cpi, (cpi->total_coded_error_left / frames_left), (int)(cpi->bits_left / frames_left), cpi->common.Height, cpi->common.Width);
- if (tmp_q < cpi->worst_quality)
- {- cpi->active_worst_quality = tmp_q;
- cpi->ni_av_qi = tmp_q;
- }
- else
- {- cpi->active_worst_quality = cpi->worst_quality;
- cpi->ni_av_qi = cpi->worst_quality;
- }
+ cpi->maxq_max_limit = cpi->worst_quality;
+ cpi->maxq_min_limit = cpi->best_quality;
+ tmp_q = estimate_max_q( cpi,
+ (cpi->total_coded_error_left / frames_left),
+ (int)(cpi->bits_left / frames_left),
+ cpi->common.Height,
+ cpi->common.Width);
+
+ // Limit the maxq value retuned subsequently.
+ // This increases the risk of overspend if the initial
+ // estimate for the clip is bad, but helps prevent excessive
+ // variation in Q, especially near the end of a clip
+ // where for example a small overspend may cause Q to crash
+ cpi->maxq_max_limit = ((tmp_q + 32) < cpi->worst_quality)
+ ? (tmp_q + 32) : cpi->worst_quality;
+ cpi->maxq_min_limit = ((tmp_q - 32) > cpi->best_quality)
+ ? (tmp_q - 32) : cpi->best_quality;
+
+ cpi->active_worst_quality = tmp_q;
+ cpi->ni_av_qi = tmp_q;
}
// The last few frames of a clip almost always have to few or too many
// bits and for the sake of over exact rate control we dont want to make
@@ -2029,13 +2039,6 @@
cpi->active_worst_quality --;
cpi->active_worst_quality = ((cpi->active_worst_quality * 3) + tmp_q + 2) / 4;
-
- // Clamp to user set limits
- if (cpi->active_worst_quality > cpi->worst_quality)
- cpi->active_worst_quality = cpi->worst_quality;
- else if (cpi->active_worst_quality < cpi->best_quality)
- cpi->active_worst_quality = cpi->best_quality;
-
}
cpi->frames_to_key --;
--- a/vp8/encoder/onyx_int.h
+++ b/vp8/encoder/onyx_int.h
@@ -447,6 +447,9 @@
int best_quality;
int active_best_quality;
+ int maxq_max_limit;
+ int maxq_min_limit;
+
int drop_frames_allowed; // Are we permitted to drop frames?
int drop_frame; // Drop this frame?
int drop_count; // How many frames have we dropped?