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Simplify 2 pass KF bitrate allocation

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Simplify the calculation of KF bitrate in similar way
to previous patch for GF/arf.

This has no impact on derf or std hd sets but gives a
small net gain of ~0.1% for yt and yt-hd sets.

Change-Id: Ida64ac1428d9c2a62adb67056fadbf0180eff030
This commit is contained in:
Paul Wilkins 2014-05-14 12:06:50 +01:00
parent d677ea1f81
commit 6122ca87a3
1 changed files with 19 additions and 75 deletions
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90
vp9/encoder/vp9_firstpass.c
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@ -1474,7 +1474,8 @@ static int calculate_boost_bits(int frame_count,
int boost, int64_t total_group_bits) {
int allocation_chunks;
if (!boost)
// return 0 for invalid inputs (could arise e.g. through rounding errors)
if (!boost || (total_group_bits <= 0) || (frame_count <= 0) )
return 0;
allocation_chunks = (frame_count * 100) + boost;
@ -2030,15 +2031,15 @@ static void find_next_key_frame(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
} else {
twopass->kf_group_bits = 0;
}
twopass->kf_group_bits = MAX(0, twopass->kf_group_bits);
// Reset the first pass file position.
reset_fpf_position(twopass, start_position);
// Determine how big to make this keyframe based on how well the subsequent
// frames use inter blocks.
// Scan through the kf group collating various stats used to deteermine
// how many bits to spend on it.
decay_accumulator = 1.0;
boost_score = 0.0;
// Scan through the kf group collating various stats.
for (i = 0; i < rc->frames_to_key; ++i) {
if (EOF == input_stats(twopass, &next_frame))
break;
@ -2075,84 +2076,27 @@ static void find_next_key_frame(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
}
}
// Store the zero motion percentage
twopass->kf_zeromotion_pct = (int)(zero_motion_accumulator * 100.0);
// Calculate a section intra ratio used in setting max loop filter.
calculate_section_intra_ratio(twopass, start_position, rc->frames_to_key);
// Work out how many bits to allocate for the key frame itself.
if (1) {
int kf_boost = (int)boost_score;
int allocation_chunks;
rc->kf_boost = (int)boost_score;
if (kf_boost < (rc->frames_to_key * 3))
kf_boost = (rc->frames_to_key * 3);
if (rc->kf_boost < (rc->frames_to_key * 3))
rc->kf_boost = (rc->frames_to_key * 3);
if (rc->kf_boost < MIN_KF_BOOST)
rc->kf_boost = MIN_KF_BOOST;
if (kf_boost < MIN_KF_BOOST)
kf_boost = MIN_KF_BOOST;
twopass->kf_bits = calculate_boost_bits((rc->frames_to_key - 1),
rc->kf_boost, twopass->kf_group_bits);
// Make a note of baseline boost and the zero motion
// accumulator value for use elsewhere.
rc->kf_boost = kf_boost;
twopass->kf_zeromotion_pct = (int)(zero_motion_accumulator * 100.0);
// Key frame size depends on:
// (1) the error score for the whole key frame group,
// (2) the key frames' own error if this is smaller than the
// average for the group (optional),
// (3) insuring that the frame receives at least the allocation it would
// have received based on its own error score vs the error score
// remaining.
// Special case:
// If the sequence appears almost totally static we want to spend almost
// all of the bits on the key frame.
//
// We use (cpi->rc.frames_to_key - 1) below because the key frame itself is
// taken care of by kf_boost.
if (zero_motion_accumulator >= 0.99) {
allocation_chunks = ((rc->frames_to_key - 1) * 10) + kf_boost;
} else {
allocation_chunks = ((rc->frames_to_key - 1) * 100) + kf_boost;
}
// Prevent overflow.
if (kf_boost > 1028) {
const int divisor = kf_boost >> 10;
kf_boost /= divisor;
allocation_chunks /= divisor;
}
twopass->kf_group_bits = MAX(0, twopass->kf_group_bits);
// Calculate the number of bits to be spent on the key frame.
twopass->kf_bits = (int)((double)kf_boost *
((double)twopass->kf_group_bits / allocation_chunks));
// If the key frame is actually easier than the average for the
// kf group (which does sometimes happen, e.g. a blank intro frame)
// then use an alternate calculation based on the kf error score
// which should give a smaller key frame.
if (kf_mod_err < kf_group_err / rc->frames_to_key) {
double alt_kf_grp_bits = ((double)twopass->bits_left *
(kf_mod_err * (double)rc->frames_to_key) /
DOUBLE_DIVIDE_CHECK(twopass->modified_error_left));
const int alt_kf_bits = (int)((double)kf_boost *
(alt_kf_grp_bits / (double)allocation_chunks));
if (twopass->kf_bits > alt_kf_bits)
twopass->kf_bits = alt_kf_bits;
} else {
// Else if it is much harder than other frames in the group make sure
// it at least receives an allocation in keeping with its relative
// error score.
const int alt_kf_bits = (int)((double)twopass->bits_left * (kf_mod_err /
DOUBLE_DIVIDE_CHECK(twopass->modified_error_left)));
if (alt_kf_bits > twopass->kf_bits)
twopass->kf_bits = alt_kf_bits;
}
twopass->kf_group_bits -= twopass->kf_bits;
// Per frame bit target for this frame.
vp9_rc_set_frame_target(cpi, twopass->kf_bits);
}
// Note the total error score of the kf group minus the key frame itself.
twopass->kf_group_error_left = (int)(kf_group_err - kf_mod_err);