// Calculate a modified Error used in distributing bits between easier and
// harder frames.
#define ACT_AREA_CORRECTION 0.5
-static double calculate_modified_err(const VP9_COMP *cpi,
- const TWO_PASS *twopass,
- const VP9EncoderConfig *oxcf,
- const FIRSTPASS_STATS *this_frame) {
+static double calculate_mod_frame_score(const VP9_COMP *cpi,
+ const TWO_PASS *twopass,
+ const VP9EncoderConfig *oxcf,
+ const FIRSTPASS_STATS *this_frame) {
const FIRSTPASS_STATS *const stats = &twopass->total_stats;
const double av_weight = stats->weight / stats->count;
const double av_err = (stats->coded_error * av_weight) / stats->count;
- double modified_error =
+ double modified_score =
av_err * pow(this_frame->coded_error * this_frame->weight /
DOUBLE_DIVIDE_CHECK(av_err),
oxcf->two_pass_vbrbias / 100.0);
// remaining active MBs. The correction here assumes that coding
// 0.5N blocks of complexity 2X is a little easier than coding N
// blocks of complexity X.
- modified_error *=
+ modified_score *=
pow(calculate_active_area(cpi, this_frame), ACT_AREA_CORRECTION);
- return fclamp(modified_error, twopass->modified_error_min,
- twopass->modified_error_max);
+ return modified_score;
+}
+static double calculate_norm_frame_score(const VP9_COMP *cpi,
+ const TWO_PASS *twopass,
+ const VP9EncoderConfig *oxcf,
+ const FIRSTPASS_STATS *this_frame) {
+ const FIRSTPASS_STATS *const stats = &twopass->total_stats;
+ const double av_weight = stats->weight / stats->count;
+ const double av_err = (stats->coded_error * av_weight) / stats->count;
+ double modified_score =
+ av_err * pow(this_frame->coded_error * this_frame->weight /
+ DOUBLE_DIVIDE_CHECK(av_err),
+ oxcf->two_pass_vbrbias / 100.0);
+
+ const double min_score = (double)(oxcf->two_pass_vbrmin_section) / 100.0;
+ const double max_score = (double)(oxcf->two_pass_vbrmax_section) / 100.0;
+
+ // Correction for active area. Frames with a reduced active area
+ // (eg due to formatting bars) have a higher error per mb for the
+ // remaining active MBs. The correction here assumes that coding
+ // 0.5N blocks of complexity 2X is a little easier than coding N
+ // blocks of complexity X.
+ modified_score *=
+ pow(calculate_active_area(cpi, this_frame), ACT_AREA_CORRECTION);
+
+ // Normalize to a midpoint score.
+ modified_score /= DOUBLE_DIVIDE_CHECK(twopass->mean_mod_score);
+
+ return fclamp(modified_score, min_score, max_score);
}
// This function returns the maximum target rate per frame.
// This variable monitors how far behind the second ref update is lagging.
twopass->sr_update_lag = 1;
- // Scan the first pass file and calculate a modified total error based upon
- // the bias/power function used to allocate bits.
+ // Scan the first pass file and calculate a modified score for each
+ // frame that is used to distribute bits. The modified score is assumed
+ // to provide a linear basis for bit allocation. I.e a frame A with a score
+ // that is double that of frame B will be allocated 2x as many bits.
{
- const double avg_error =
- stats->coded_error / DOUBLE_DIVIDE_CHECK(stats->count);
const FIRSTPASS_STATS *s = twopass->stats_in;
- double modified_error_total = 0.0;
- twopass->modified_error_min =
- (avg_error * oxcf->two_pass_vbrmin_section) / 100;
- twopass->modified_error_max =
- (avg_error * oxcf->two_pass_vbrmax_section) / 100;
+ double modified_score_total = 0.0;
+
+ // The first scan is unclamped and gives a raw average.
+ while (s < twopass->stats_in_end) {
+ modified_score_total += calculate_mod_frame_score(cpi, twopass, oxcf, s);
+ ++s;
+ }
+
+ // The average error from this first scan is used to define the midpoint
+ // error for the rate distribution function.
+ twopass->mean_mod_score =
+ modified_score_total / DOUBLE_DIVIDE_CHECK(stats->count);
+
+ // Second scan using clamps based on the previous cycle average.
+ // This may modify the total and average somewhat but we dont bother with
+ // further itterations.
+ s = twopass->stats_in;
+ modified_score_total = 0.0;
while (s < twopass->stats_in_end) {
- modified_error_total += calculate_modified_err(cpi, twopass, oxcf, s);
+ modified_score_total += calculate_norm_frame_score(cpi, twopass, oxcf, s);
++s;
}
- twopass->modified_error_left = modified_error_total;
+ twopass->normalized_score_left = modified_score_total;
}
// Reset the vbr bits off target counters
vp9_zero(next_frame);
// Load stats for the current frame.
- mod_frame_err = calculate_modified_err(cpi, twopass, oxcf, this_frame);
+ mod_frame_err = calculate_norm_frame_score(cpi, twopass, oxcf, this_frame);
// Note the error of the frame at the start of the group. This will be
// the GF frame error if we code a normal gf.
++i;
// Accumulate error score of frames in this gf group.
- mod_frame_err = calculate_modified_err(cpi, twopass, oxcf, this_frame);
+ mod_frame_err = calculate_norm_frame_score(cpi, twopass, oxcf, this_frame);
gf_group_err += mod_frame_err;
gf_group_raw_error += this_frame->coded_error;
gf_group_noise += this_frame->frame_noise_energy;
int j;
for (j = 0; j < new_gf_interval - rc->baseline_gf_interval; ++j) {
if (EOF == input_stats(twopass, this_frame)) break;
- gf_group_err += calculate_modified_err(cpi, twopass, oxcf, this_frame);
+ gf_group_err +=
+ calculate_norm_frame_score(cpi, twopass, oxcf, this_frame);
gf_group_raw_error += this_frame->coded_error;
gf_group_noise += this_frame->frame_noise_energy;
gf_group_skip_pct += this_frame->intra_skip_pct;
twopass->kf_group_bits = 0; // Total bits available to kf group
twopass->kf_group_error_left = 0.0; // Group modified error score.
- kf_mod_err = calculate_modified_err(cpi, twopass, oxcf, this_frame);
+ kf_mod_err = calculate_norm_frame_score(cpi, twopass, oxcf, this_frame);
// Initialize the decay rates for the recent frames to check
for (j = 0; j < FRAMES_TO_CHECK_DECAY; ++j) recent_loop_decay[j] = 1.0;
while (twopass->stats_in < twopass->stats_in_end &&
rc->frames_to_key < cpi->oxcf.key_freq) {
// Accumulate kf group error.
- kf_group_err += calculate_modified_err(cpi, twopass, oxcf, this_frame);
+ kf_group_err += calculate_norm_frame_score(cpi, twopass, oxcf, this_frame);
// Load the next frame's stats.
last_frame = *this_frame;
// Rescan to get the correct error data for the forced kf group.
for (i = 0; i < rc->frames_to_key; ++i) {
- kf_group_err += calculate_modified_err(cpi, twopass, oxcf, &tmp_frame);
+ kf_group_err +=
+ calculate_norm_frame_score(cpi, twopass, oxcf, &tmp_frame);
input_stats(twopass, &tmp_frame);
}
rc->next_key_frame_forced = 1;
int j;
for (j = 0; j < new_frame_to_key - rc->frames_to_key; ++j) {
if (EOF == input_stats(twopass, this_frame)) break;
- kf_group_err += calculate_modified_err(cpi, twopass, oxcf, this_frame);
+ kf_group_err +=
+ calculate_norm_frame_score(cpi, twopass, oxcf, this_frame);
}
rc->frames_to_key = new_frame_to_key;
}
// Special case for the last key frame of the file.
if (twopass->stats_in >= twopass->stats_in_end) {
// Accumulate kf group error.
- kf_group_err += calculate_modified_err(cpi, twopass, oxcf, this_frame);
+ kf_group_err += calculate_norm_frame_score(cpi, twopass, oxcf, this_frame);
}
// Calculate the number of bits that should be assigned to the kf group.
- if (twopass->bits_left > 0 && twopass->modified_error_left > 0.0) {
+ if (twopass->bits_left > 0 && twopass->normalized_score_left > 0.0) {
// Maximum number of bits for a single normal frame (not key frame).
const int max_bits = frame_max_bits(rc, &cpi->oxcf);
// Default allocation based on bits left and relative
// complexity of the section.
twopass->kf_group_bits = (int64_t)(
- twopass->bits_left * (kf_group_err / twopass->modified_error_left));
+ twopass->bits_left * (kf_group_err / twopass->normalized_score_left));
// Clip based on maximum per frame rate defined by the user.
max_grp_bits = (int64_t)max_bits * (int64_t)rc->frames_to_key;
// Adjust the count of total modified error left.
// The count of bits left is adjusted elsewhere based on real coded frame
// sizes.
- twopass->modified_error_left -= kf_group_err;
+ twopass->normalized_score_left -= kf_group_err;
if (oxcf->resize_mode == RESIZE_DYNAMIC) {
// Default to normal-sized frame on keyframes.
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