ref: 48ea5b719041df2988736c53e16f73cf6ed2e67a
dir: /vp9/encoder/vp9_bitstream.c/
/*
* Copyright (c) 2010 The WebM project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include <assert.h>
#include <stdio.h>
#include <limits.h>
#include "vpx/vpx_encoder.h"
#include "vpx_mem/vpx_mem.h"
#include "vpx_ports/mem_ops.h"
#include "vp9/common/vp9_entropy.h"
#include "vp9/common/vp9_entropymode.h"
#include "vp9/common/vp9_entropymv.h"
#include "vp9/common/vp9_mvref_common.h"
#include "vp9/common/vp9_pred_common.h"
#include "vp9/common/vp9_seg_common.h"
#include "vp9/common/vp9_systemdependent.h"
#include "vp9/common/vp9_tile_common.h"
#include "vp9/encoder/vp9_cost.h"
#include "vp9/encoder/vp9_bitstream.h"
#include "vp9/encoder/vp9_encodemv.h"
#include "vp9/encoder/vp9_mcomp.h"
#include "vp9/encoder/vp9_segmentation.h"
#include "vp9/encoder/vp9_subexp.h"
#include "vp9/encoder/vp9_tokenize.h"
#include "vp9/encoder/vp9_write_bit_buffer.h"
static struct vp9_token intra_mode_encodings[INTRA_MODES];
static struct vp9_token switchable_interp_encodings[SWITCHABLE_FILTERS];
static struct vp9_token partition_encodings[PARTITION_TYPES];
static struct vp9_token inter_mode_encodings[INTER_MODES];
void vp9_entropy_mode_init() {
vp9_tokens_from_tree(intra_mode_encodings, vp9_intra_mode_tree);
vp9_tokens_from_tree(switchable_interp_encodings, vp9_switchable_interp_tree);
vp9_tokens_from_tree(partition_encodings, vp9_partition_tree);
vp9_tokens_from_tree(inter_mode_encodings, vp9_inter_mode_tree);
}
static void write_intra_mode(vp9_writer *w, PREDICTION_MODE mode,
const vp9_prob *probs) {
vp9_write_token(w, vp9_intra_mode_tree, probs, &intra_mode_encodings[mode]);
}
static void write_inter_mode(vp9_writer *w, PREDICTION_MODE mode,
const vp9_prob *probs) {
assert(is_inter_mode(mode));
vp9_write_token(w, vp9_inter_mode_tree, probs,
&inter_mode_encodings[INTER_OFFSET(mode)]);
}
static void encode_unsigned_max(struct vp9_write_bit_buffer *wb,
int data, int max) {
vp9_wb_write_literal(wb, data, get_unsigned_bits(max));
}
static void prob_diff_update(const vp9_tree_index *tree,
vp9_prob probs[/*n - 1*/],
const unsigned int counts[/*n - 1*/],
int n, vp9_writer *w) {
int i;
unsigned int branch_ct[32][2];
// Assuming max number of probabilities <= 32
assert(n <= 32);
vp9_tree_probs_from_distribution(tree, branch_ct, counts);
for (i = 0; i < n - 1; ++i)
vp9_cond_prob_diff_update(w, &probs[i], branch_ct[i]);
}
static void write_selected_tx_size(const VP9_COMMON *cm,
const MACROBLOCKD *xd,
TX_SIZE tx_size, BLOCK_SIZE bsize,
vp9_writer *w) {
const TX_SIZE max_tx_size = max_txsize_lookup[bsize];
const vp9_prob *const tx_probs = get_tx_probs2(max_tx_size, xd,
&cm->fc.tx_probs);
vp9_write(w, tx_size != TX_4X4, tx_probs[0]);
if (tx_size != TX_4X4 && max_tx_size >= TX_16X16) {
vp9_write(w, tx_size != TX_8X8, tx_probs[1]);
if (tx_size != TX_8X8 && max_tx_size >= TX_32X32)
vp9_write(w, tx_size != TX_16X16, tx_probs[2]);
}
}
static int write_skip(const VP9_COMMON *cm, const MACROBLOCKD *xd,
int segment_id, const MODE_INFO *mi, vp9_writer *w) {
if (vp9_segfeature_active(&cm->seg, segment_id, SEG_LVL_SKIP)) {
return 1;
} else {
const int skip = mi->mbmi.skip;
vp9_write(w, skip, vp9_get_skip_prob(cm, xd));
return skip;
}
}
static void update_skip_probs(VP9_COMMON *cm, vp9_writer *w) {
int k;
for (k = 0; k < SKIP_CONTEXTS; ++k)
vp9_cond_prob_diff_update(w, &cm->fc.skip_probs[k], cm->counts.skip[k]);
}
static void update_switchable_interp_probs(VP9_COMMON *cm, vp9_writer *w) {
int j;
for (j = 0; j < SWITCHABLE_FILTER_CONTEXTS; ++j)
prob_diff_update(vp9_switchable_interp_tree,
cm->fc.switchable_interp_prob[j],
cm->counts.switchable_interp[j], SWITCHABLE_FILTERS, w);
}
static void pack_mb_tokens(vp9_writer *w,
TOKENEXTRA **tp, const TOKENEXTRA *const stop,
vpx_bit_depth_t bit_depth) {
TOKENEXTRA *p = *tp;
while (p < stop && p->token != EOSB_TOKEN) {
const int t = p->token;
const struct vp9_token *const a = &vp9_coef_encodings[t];
int i = 0;
int v = a->value;
int n = a->len;
#if CONFIG_VP9_HIGHBITDEPTH
const vp9_extra_bit *b;
if (bit_depth == VPX_BITS_12)
b = &vp9_extra_bits_high12[t];
else if (bit_depth == VPX_BITS_10)
b = &vp9_extra_bits_high10[t];
else
b = &vp9_extra_bits[t];
#else
const vp9_extra_bit *const b = &vp9_extra_bits[t];
(void) bit_depth;
#endif // CONFIG_VP9_HIGHBITDEPTH
/* skip one or two nodes */
if (p->skip_eob_node) {
n -= p->skip_eob_node;
i = 2 * p->skip_eob_node;
}
// TODO(jbb): expanding this can lead to big gains. It allows
// much better branch prediction and would enable us to avoid numerous
// lookups and compares.
// If we have a token that's in the constrained set, the coefficient tree
// is split into two treed writes. The first treed write takes care of the
// unconstrained nodes. The second treed write takes care of the
// constrained nodes.
if (t >= TWO_TOKEN && t < EOB_TOKEN) {
int len = UNCONSTRAINED_NODES - p->skip_eob_node;
int bits = v >> (n - len);
vp9_write_tree(w, vp9_coef_tree, p->context_tree, bits, len, i);
vp9_write_tree(w, vp9_coef_con_tree,
vp9_pareto8_full[p->context_tree[PIVOT_NODE] - 1],
v, n - len, 0);
} else {
vp9_write_tree(w, vp9_coef_tree, p->context_tree, v, n, i);
}
if (b->base_val) {
const int e = p->extra, l = b->len;
if (l) {
const unsigned char *pb = b->prob;
int v = e >> 1;
int n = l; /* number of bits in v, assumed nonzero */
int i = 0;
do {
const int bb = (v >> --n) & 1;
vp9_write(w, bb, pb[i >> 1]);
i = b->tree[i + bb];
} while (n);
}
vp9_write_bit(w, e & 1);
}
++p;
}
*tp = p + (p->token == EOSB_TOKEN);
}
static void write_segment_id(vp9_writer *w, const struct segmentation *seg,
int segment_id) {
if (seg->enabled && seg->update_map)
vp9_write_tree(w, vp9_segment_tree, seg->tree_probs, segment_id, 3, 0);
}
// This function encodes the reference frame
static void write_ref_frames(const VP9_COMMON *cm, const MACROBLOCKD *xd,
vp9_writer *w) {
const MB_MODE_INFO *const mbmi = &xd->mi[0].src_mi->mbmi;
const int is_compound = has_second_ref(mbmi);
const int segment_id = mbmi->segment_id;
// If segment level coding of this signal is disabled...
// or the segment allows multiple reference frame options
if (vp9_segfeature_active(&cm->seg, segment_id, SEG_LVL_REF_FRAME)) {
assert(!is_compound);
assert(mbmi->ref_frame[0] ==
vp9_get_segdata(&cm->seg, segment_id, SEG_LVL_REF_FRAME));
} else {
// does the feature use compound prediction or not
// (if not specified at the frame/segment level)
if (cm->reference_mode == REFERENCE_MODE_SELECT) {
vp9_write(w, is_compound, vp9_get_reference_mode_prob(cm, xd));
} else {
assert(!is_compound == (cm->reference_mode == SINGLE_REFERENCE));
}
if (is_compound) {
vp9_write(w, mbmi->ref_frame[0] == GOLDEN_FRAME,
vp9_get_pred_prob_comp_ref_p(cm, xd));
} else {
const int bit0 = mbmi->ref_frame[0] != LAST_FRAME;
vp9_write(w, bit0, vp9_get_pred_prob_single_ref_p1(cm, xd));
if (bit0) {
const int bit1 = mbmi->ref_frame[0] != GOLDEN_FRAME;
vp9_write(w, bit1, vp9_get_pred_prob_single_ref_p2(cm, xd));
}
}
}
}
static void pack_inter_mode_mvs(VP9_COMP *cpi, const MODE_INFO *mi,
vp9_writer *w) {
VP9_COMMON *const cm = &cpi->common;
const nmv_context *nmvc = &cm->fc.nmvc;
const MACROBLOCK *const x = &cpi->mb;
const MACROBLOCKD *const xd = &x->e_mbd;
const struct segmentation *const seg = &cm->seg;
const MB_MODE_INFO *const mbmi = &mi->mbmi;
const PREDICTION_MODE mode = mbmi->mode;
const int segment_id = mbmi->segment_id;
const BLOCK_SIZE bsize = mbmi->sb_type;
const int allow_hp = cm->allow_high_precision_mv;
const int is_inter = is_inter_block(mbmi);
const int is_compound = has_second_ref(mbmi);
int skip, ref;
if (seg->update_map) {
if (seg->temporal_update) {
const int pred_flag = mbmi->seg_id_predicted;
vp9_prob pred_prob = vp9_get_pred_prob_seg_id(seg, xd);
vp9_write(w, pred_flag, pred_prob);
if (!pred_flag)
write_segment_id(w, seg, segment_id);
} else {
write_segment_id(w, seg, segment_id);
}
}
skip = write_skip(cm, xd, segment_id, mi, w);
if (!vp9_segfeature_active(seg, segment_id, SEG_LVL_REF_FRAME))
vp9_write(w, is_inter, vp9_get_intra_inter_prob(cm, xd));
if (bsize >= BLOCK_8X8 && cm->tx_mode == TX_MODE_SELECT &&
!(is_inter &&
(skip || vp9_segfeature_active(seg, segment_id, SEG_LVL_SKIP)))) {
write_selected_tx_size(cm, xd, mbmi->tx_size, bsize, w);
}
if (!is_inter) {
if (bsize >= BLOCK_8X8) {
write_intra_mode(w, mode, cm->fc.y_mode_prob[size_group_lookup[bsize]]);
} else {
int idx, idy;
const int num_4x4_w = num_4x4_blocks_wide_lookup[bsize];
const int num_4x4_h = num_4x4_blocks_high_lookup[bsize];
for (idy = 0; idy < 2; idy += num_4x4_h) {
for (idx = 0; idx < 2; idx += num_4x4_w) {
const PREDICTION_MODE b_mode = mi->bmi[idy * 2 + idx].as_mode;
write_intra_mode(w, b_mode, cm->fc.y_mode_prob[0]);
}
}
}
write_intra_mode(w, mbmi->uv_mode, cm->fc.uv_mode_prob[mode]);
} else {
const int mode_ctx = mbmi->mode_context[mbmi->ref_frame[0]];
const vp9_prob *const inter_probs = cm->fc.inter_mode_probs[mode_ctx];
write_ref_frames(cm, xd, w);
// If segment skip is not enabled code the mode.
if (!vp9_segfeature_active(seg, segment_id, SEG_LVL_SKIP)) {
if (bsize >= BLOCK_8X8) {
write_inter_mode(w, mode, inter_probs);
++cm->counts.inter_mode[mode_ctx][INTER_OFFSET(mode)];
}
}
if (cm->interp_filter == SWITCHABLE) {
const int ctx = vp9_get_pred_context_switchable_interp(xd);
vp9_write_token(w, vp9_switchable_interp_tree,
cm->fc.switchable_interp_prob[ctx],
&switchable_interp_encodings[mbmi->interp_filter]);
++cpi->interp_filter_selected[0][mbmi->interp_filter];
} else {
assert(mbmi->interp_filter == cm->interp_filter);
}
if (bsize < BLOCK_8X8) {
const int num_4x4_w = num_4x4_blocks_wide_lookup[bsize];
const int num_4x4_h = num_4x4_blocks_high_lookup[bsize];
int idx, idy;
for (idy = 0; idy < 2; idy += num_4x4_h) {
for (idx = 0; idx < 2; idx += num_4x4_w) {
const int j = idy * 2 + idx;
const PREDICTION_MODE b_mode = mi->bmi[j].as_mode;
write_inter_mode(w, b_mode, inter_probs);
++cm->counts.inter_mode[mode_ctx][INTER_OFFSET(b_mode)];
if (b_mode == NEWMV) {
for (ref = 0; ref < 1 + is_compound; ++ref)
vp9_encode_mv(cpi, w, &mi->bmi[j].as_mv[ref].as_mv,
&mbmi->ref_mvs[mbmi->ref_frame[ref]][0].as_mv,
nmvc, allow_hp);
}
}
}
} else {
if (mode == NEWMV) {
for (ref = 0; ref < 1 + is_compound; ++ref)
vp9_encode_mv(cpi, w, &mbmi->mv[ref].as_mv,
&mbmi->ref_mvs[mbmi->ref_frame[ref]][0].as_mv, nmvc,
allow_hp);
}
}
}
}
static void write_mb_modes_kf(const VP9_COMMON *cm, const MACROBLOCKD *xd,
MODE_INFO *mi_8x8, vp9_writer *w) {
const struct segmentation *const seg = &cm->seg;
const MODE_INFO *const mi = mi_8x8;
const MODE_INFO *const above_mi = mi_8x8[-xd->mi_stride].src_mi;
const MODE_INFO *const left_mi =
xd->left_available ? mi_8x8[-1].src_mi : NULL;
const MB_MODE_INFO *const mbmi = &mi->mbmi;
const BLOCK_SIZE bsize = mbmi->sb_type;
if (seg->update_map)
write_segment_id(w, seg, mbmi->segment_id);
write_skip(cm, xd, mbmi->segment_id, mi, w);
if (bsize >= BLOCK_8X8 && cm->tx_mode == TX_MODE_SELECT)
write_selected_tx_size(cm, xd, mbmi->tx_size, bsize, w);
if (bsize >= BLOCK_8X8) {
write_intra_mode(w, mbmi->mode, get_y_mode_probs(mi, above_mi, left_mi, 0));
} else {
const int num_4x4_w = num_4x4_blocks_wide_lookup[bsize];
const int num_4x4_h = num_4x4_blocks_high_lookup[bsize];
int idx, idy;
for (idy = 0; idy < 2; idy += num_4x4_h) {
for (idx = 0; idx < 2; idx += num_4x4_w) {
const int block = idy * 2 + idx;
write_intra_mode(w, mi->bmi[block].as_mode,
get_y_mode_probs(mi, above_mi, left_mi, block));
}
}
}
write_intra_mode(w, mbmi->uv_mode, vp9_kf_uv_mode_prob[mbmi->mode]);
}
static void write_modes_b(VP9_COMP *cpi, const TileInfo *const tile,
vp9_writer *w, TOKENEXTRA **tok,
const TOKENEXTRA *const tok_end,
int mi_row, int mi_col) {
const VP9_COMMON *const cm = &cpi->common;
MACROBLOCKD *const xd = &cpi->mb.e_mbd;
MODE_INFO *m;
xd->mi = cm->mi + (mi_row * cm->mi_stride + mi_col);
m = xd->mi;
set_mi_row_col(xd, tile,
mi_row, num_8x8_blocks_high_lookup[m->mbmi.sb_type],
mi_col, num_8x8_blocks_wide_lookup[m->mbmi.sb_type],
cm->mi_rows, cm->mi_cols);
if (frame_is_intra_only(cm)) {
write_mb_modes_kf(cm, xd, xd->mi, w);
} else {
pack_inter_mode_mvs(cpi, m, w);
}
assert(*tok < tok_end);
pack_mb_tokens(w, tok, tok_end, cm->bit_depth);
}
static void write_partition(const VP9_COMMON *const cm,
const MACROBLOCKD *const xd,
int hbs, int mi_row, int mi_col,
PARTITION_TYPE p, BLOCK_SIZE bsize, vp9_writer *w) {
const int ctx = partition_plane_context(xd, mi_row, mi_col, bsize);
const vp9_prob *const probs = get_partition_probs(cm, ctx);
const int has_rows = (mi_row + hbs) < cm->mi_rows;
const int has_cols = (mi_col + hbs) < cm->mi_cols;
if (has_rows && has_cols) {
vp9_write_token(w, vp9_partition_tree, probs, &partition_encodings[p]);
} else if (!has_rows && has_cols) {
assert(p == PARTITION_SPLIT || p == PARTITION_HORZ);
vp9_write(w, p == PARTITION_SPLIT, probs[1]);
} else if (has_rows && !has_cols) {
assert(p == PARTITION_SPLIT || p == PARTITION_VERT);
vp9_write(w, p == PARTITION_SPLIT, probs[2]);
} else {
assert(p == PARTITION_SPLIT);
}
}
static void write_modes_sb(VP9_COMP *cpi,
const TileInfo *const tile, vp9_writer *w,
TOKENEXTRA **tok, const TOKENEXTRA *const tok_end,
int mi_row, int mi_col, BLOCK_SIZE bsize) {
const VP9_COMMON *const cm = &cpi->common;
MACROBLOCKD *const xd = &cpi->mb.e_mbd;
const int bsl = b_width_log2_lookup[bsize];
const int bs = (1 << bsl) / 4;
PARTITION_TYPE partition;
BLOCK_SIZE subsize;
const MODE_INFO *m = NULL;
if (mi_row >= cm->mi_rows || mi_col >= cm->mi_cols)
return;
m = cm->mi[mi_row * cm->mi_stride + mi_col].src_mi;
partition = partition_lookup[bsl][m->mbmi.sb_type];
write_partition(cm, xd, bs, mi_row, mi_col, partition, bsize, w);
subsize = get_subsize(bsize, partition);
if (subsize < BLOCK_8X8) {
write_modes_b(cpi, tile, w, tok, tok_end, mi_row, mi_col);
} else {
switch (partition) {
case PARTITION_NONE:
write_modes_b(cpi, tile, w, tok, tok_end, mi_row, mi_col);
break;
case PARTITION_HORZ:
write_modes_b(cpi, tile, w, tok, tok_end, mi_row, mi_col);
if (mi_row + bs < cm->mi_rows)
write_modes_b(cpi, tile, w, tok, tok_end, mi_row + bs, mi_col);
break;
case PARTITION_VERT:
write_modes_b(cpi, tile, w, tok, tok_end, mi_row, mi_col);
if (mi_col + bs < cm->mi_cols)
write_modes_b(cpi, tile, w, tok, tok_end, mi_row, mi_col + bs);
break;
case PARTITION_SPLIT:
write_modes_sb(cpi, tile, w, tok, tok_end, mi_row, mi_col, subsize);
write_modes_sb(cpi, tile, w, tok, tok_end, mi_row, mi_col + bs,
subsize);
write_modes_sb(cpi, tile, w, tok, tok_end, mi_row + bs, mi_col,
subsize);
write_modes_sb(cpi, tile, w, tok, tok_end, mi_row + bs, mi_col + bs,
subsize);
break;
default:
assert(0);
}
}
// update partition context
if (bsize >= BLOCK_8X8 &&
(bsize == BLOCK_8X8 || partition != PARTITION_SPLIT))
update_partition_context(xd, mi_row, mi_col, subsize, bsize);
}
static void write_modes(VP9_COMP *cpi,
const TileInfo *const tile, vp9_writer *w,
TOKENEXTRA **tok, const TOKENEXTRA *const tok_end) {
int mi_row, mi_col;
for (mi_row = tile->mi_row_start; mi_row < tile->mi_row_end;
mi_row += MI_BLOCK_SIZE) {
vp9_zero(cpi->mb.e_mbd.left_seg_context);
for (mi_col = tile->mi_col_start; mi_col < tile->mi_col_end;
mi_col += MI_BLOCK_SIZE)
write_modes_sb(cpi, tile, w, tok, tok_end, mi_row, mi_col,
BLOCK_64X64);
}
}
static void build_tree_distribution(VP9_COMP *cpi, TX_SIZE tx_size,
vp9_coeff_stats *coef_branch_ct,
vp9_coeff_probs_model *coef_probs) {
vp9_coeff_count *coef_counts = cpi->coef_counts[tx_size];
unsigned int (*eob_branch_ct)[REF_TYPES][COEF_BANDS][COEFF_CONTEXTS] =
cpi->common.counts.eob_branch[tx_size];
int i, j, k, l, m;
for (i = 0; i < PLANE_TYPES; ++i) {
for (j = 0; j < REF_TYPES; ++j) {
for (k = 0; k < COEF_BANDS; ++k) {
for (l = 0; l < BAND_COEFF_CONTEXTS(k); ++l) {
vp9_tree_probs_from_distribution(vp9_coef_tree,
coef_branch_ct[i][j][k][l],
coef_counts[i][j][k][l]);
coef_branch_ct[i][j][k][l][0][1] = eob_branch_ct[i][j][k][l] -
coef_branch_ct[i][j][k][l][0][0];
for (m = 0; m < UNCONSTRAINED_NODES; ++m)
coef_probs[i][j][k][l][m] = get_binary_prob(
coef_branch_ct[i][j][k][l][m][0],
coef_branch_ct[i][j][k][l][m][1]);
}
}
}
}
}
static void update_coef_probs_common(vp9_writer* const bc, VP9_COMP *cpi,
TX_SIZE tx_size,
vp9_coeff_stats *frame_branch_ct,
vp9_coeff_probs_model *new_coef_probs) {
vp9_coeff_probs_model *old_coef_probs = cpi->common.fc.coef_probs[tx_size];
const vp9_prob upd = DIFF_UPDATE_PROB;
const int entropy_nodes_update = UNCONSTRAINED_NODES;
int i, j, k, l, t;
switch (cpi->sf.use_fast_coef_updates) {
case TWO_LOOP: {
/* dry run to see if there is any update at all needed */
int savings = 0;
int update[2] = {0, 0};
for (i = 0; i < PLANE_TYPES; ++i) {
for (j = 0; j < REF_TYPES; ++j) {
for (k = 0; k < COEF_BANDS; ++k) {
for (l = 0; l < BAND_COEFF_CONTEXTS(k); ++l) {
for (t = 0; t < entropy_nodes_update; ++t) {
vp9_prob newp = new_coef_probs[i][j][k][l][t];
const vp9_prob oldp = old_coef_probs[i][j][k][l][t];
int s;
int u = 0;
if (t == PIVOT_NODE)
s = vp9_prob_diff_update_savings_search_model(
frame_branch_ct[i][j][k][l][0],
old_coef_probs[i][j][k][l], &newp, upd);
else
s = vp9_prob_diff_update_savings_search(
frame_branch_ct[i][j][k][l][t], oldp, &newp, upd);
if (s > 0 && newp != oldp)
u = 1;
if (u)
savings += s - (int)(vp9_cost_zero(upd));
else
savings -= (int)(vp9_cost_zero(upd));
update[u]++;
}
}
}
}
}
// printf("Update %d %d, savings %d\n", update[0], update[1], savings);
/* Is coef updated at all */
if (update[1] == 0 || savings < 0) {
vp9_write_bit(bc, 0);
return;
}
vp9_write_bit(bc, 1);
for (i = 0; i < PLANE_TYPES; ++i) {
for (j = 0; j < REF_TYPES; ++j) {
for (k = 0; k < COEF_BANDS; ++k) {
for (l = 0; l < BAND_COEFF_CONTEXTS(k); ++l) {
// calc probs and branch cts for this frame only
for (t = 0; t < entropy_nodes_update; ++t) {
vp9_prob newp = new_coef_probs[i][j][k][l][t];
vp9_prob *oldp = old_coef_probs[i][j][k][l] + t;
const vp9_prob upd = DIFF_UPDATE_PROB;
int s;
int u = 0;
if (t == PIVOT_NODE)
s = vp9_prob_diff_update_savings_search_model(
frame_branch_ct[i][j][k][l][0],
old_coef_probs[i][j][k][l], &newp, upd);
else
s = vp9_prob_diff_update_savings_search(
frame_branch_ct[i][j][k][l][t],
*oldp, &newp, upd);
if (s > 0 && newp != *oldp)
u = 1;
vp9_write(bc, u, upd);
if (u) {
/* send/use new probability */
vp9_write_prob_diff_update(bc, newp, *oldp);
*oldp = newp;
}
}
}
}
}
}
return;
}
case ONE_LOOP:
case ONE_LOOP_REDUCED: {
const int prev_coef_contexts_to_update =
cpi->sf.use_fast_coef_updates == ONE_LOOP_REDUCED ?
COEFF_CONTEXTS >> 1 : COEFF_CONTEXTS;
const int coef_band_to_update =
cpi->sf.use_fast_coef_updates == ONE_LOOP_REDUCED ?
COEF_BANDS >> 1 : COEF_BANDS;
int updates = 0;
int noupdates_before_first = 0;
for (i = 0; i < PLANE_TYPES; ++i) {
for (j = 0; j < REF_TYPES; ++j) {
for (k = 0; k < COEF_BANDS; ++k) {
for (l = 0; l < BAND_COEFF_CONTEXTS(k); ++l) {
// calc probs and branch cts for this frame only
for (t = 0; t < entropy_nodes_update; ++t) {
vp9_prob newp = new_coef_probs[i][j][k][l][t];
vp9_prob *oldp = old_coef_probs[i][j][k][l] + t;
int s;
int u = 0;
if (l >= prev_coef_contexts_to_update ||
k >= coef_band_to_update) {
u = 0;
} else {
if (t == PIVOT_NODE)
s = vp9_prob_diff_update_savings_search_model(
frame_branch_ct[i][j][k][l][0],
old_coef_probs[i][j][k][l], &newp, upd);
else
s = vp9_prob_diff_update_savings_search(
frame_branch_ct[i][j][k][l][t],
*oldp, &newp, upd);
if (s > 0 && newp != *oldp)
u = 1;
}
updates += u;
if (u == 0 && updates == 0) {
noupdates_before_first++;
continue;
}
if (u == 1 && updates == 1) {
int v;
// first update
vp9_write_bit(bc, 1);
for (v = 0; v < noupdates_before_first; ++v)
vp9_write(bc, 0, upd);
}
vp9_write(bc, u, upd);
if (u) {
/* send/use new probability */
vp9_write_prob_diff_update(bc, newp, *oldp);
*oldp = newp;
}
}
}
}
}
}
if (updates == 0) {
vp9_write_bit(bc, 0); // no updates
}
return;
}
default:
assert(0);
}
}
static void update_coef_probs(VP9_COMP *cpi, vp9_writer* w) {
const TX_MODE tx_mode = cpi->common.tx_mode;
const TX_SIZE max_tx_size = tx_mode_to_biggest_tx_size[tx_mode];
TX_SIZE tx_size;
vp9_coeff_stats frame_branch_ct[TX_SIZES][PLANE_TYPES];
vp9_coeff_probs_model frame_coef_probs[TX_SIZES][PLANE_TYPES];
for (tx_size = TX_4X4; tx_size <= TX_32X32; ++tx_size)
build_tree_distribution(cpi, tx_size, frame_branch_ct[tx_size],
frame_coef_probs[tx_size]);
for (tx_size = TX_4X4; tx_size <= max_tx_size; ++tx_size)
update_coef_probs_common(w, cpi, tx_size, frame_branch_ct[tx_size],
frame_coef_probs[tx_size]);
}
static void encode_loopfilter(struct loopfilter *lf,
struct vp9_write_bit_buffer *wb) {
int i;
// Encode the loop filter level and type
vp9_wb_write_literal(wb, lf->filter_level, 6);
vp9_wb_write_literal(wb, lf->sharpness_level, 3);
// Write out loop filter deltas applied at the MB level based on mode or
// ref frame (if they are enabled).
vp9_wb_write_bit(wb, lf->mode_ref_delta_enabled);
if (lf->mode_ref_delta_enabled) {
vp9_wb_write_bit(wb, lf->mode_ref_delta_update);
if (lf->mode_ref_delta_update) {
for (i = 0; i < MAX_REF_LF_DELTAS; i++) {
const int delta = lf->ref_deltas[i];
const int changed = delta != lf->last_ref_deltas[i];
vp9_wb_write_bit(wb, changed);
if (changed) {
lf->last_ref_deltas[i] = delta;
vp9_wb_write_literal(wb, abs(delta) & 0x3F, 6);
vp9_wb_write_bit(wb, delta < 0);
}
}
for (i = 0; i < MAX_MODE_LF_DELTAS; i++) {
const int delta = lf->mode_deltas[i];
const int changed = delta != lf->last_mode_deltas[i];
vp9_wb_write_bit(wb, changed);
if (changed) {
lf->last_mode_deltas[i] = delta;
vp9_wb_write_literal(wb, abs(delta) & 0x3F, 6);
vp9_wb_write_bit(wb, delta < 0);
}
}
}
}
}
static void write_delta_q(struct vp9_write_bit_buffer *wb, int delta_q) {
if (delta_q != 0) {
vp9_wb_write_bit(wb, 1);
vp9_wb_write_literal(wb, abs(delta_q), 4);
vp9_wb_write_bit(wb, delta_q < 0);
} else {
vp9_wb_write_bit(wb, 0);
}
}
static void encode_quantization(const VP9_COMMON *const cm,
struct vp9_write_bit_buffer *wb) {
vp9_wb_write_literal(wb, cm->base_qindex, QINDEX_BITS);
write_delta_q(wb, cm->y_dc_delta_q);
write_delta_q(wb, cm->uv_dc_delta_q);
write_delta_q(wb, cm->uv_ac_delta_q);
}
static void encode_segmentation(VP9_COMMON *cm, MACROBLOCKD *xd,
struct vp9_write_bit_buffer *wb) {
int i, j;
const struct segmentation *seg = &cm->seg;
vp9_wb_write_bit(wb, seg->enabled);
if (!seg->enabled)
return;
// Segmentation map
vp9_wb_write_bit(wb, seg->update_map);
if (seg->update_map) {
// Select the coding strategy (temporal or spatial)
vp9_choose_segmap_coding_method(cm, xd);
// Write out probabilities used to decode unpredicted macro-block segments
for (i = 0; i < SEG_TREE_PROBS; i++) {
const int prob = seg->tree_probs[i];
const int update = prob != MAX_PROB;
vp9_wb_write_bit(wb, update);
if (update)
vp9_wb_write_literal(wb, prob, 8);
}
// Write out the chosen coding method.
vp9_wb_write_bit(wb, seg->temporal_update);
if (seg->temporal_update) {
for (i = 0; i < PREDICTION_PROBS; i++) {
const int prob = seg->pred_probs[i];
const int update = prob != MAX_PROB;
vp9_wb_write_bit(wb, update);
if (update)
vp9_wb_write_literal(wb, prob, 8);
}
}
}
// Segmentation data
vp9_wb_write_bit(wb, seg->update_data);
if (seg->update_data) {
vp9_wb_write_bit(wb, seg->abs_delta);
for (i = 0; i < MAX_SEGMENTS; i++) {
for (j = 0; j < SEG_LVL_MAX; j++) {
const int active = vp9_segfeature_active(seg, i, j);
vp9_wb_write_bit(wb, active);
if (active) {
const int data = vp9_get_segdata(seg, i, j);
const int data_max = vp9_seg_feature_data_max(j);
if (vp9_is_segfeature_signed(j)) {
encode_unsigned_max(wb, abs(data), data_max);
vp9_wb_write_bit(wb, data < 0);
} else {
encode_unsigned_max(wb, data, data_max);
}
}
}
}
}
}
static void encode_txfm_probs(VP9_COMMON *cm, vp9_writer *w) {
// Mode
vp9_write_literal(w, MIN(cm->tx_mode, ALLOW_32X32), 2);
if (cm->tx_mode >= ALLOW_32X32)
vp9_write_bit(w, cm->tx_mode == TX_MODE_SELECT);
// Probabilities
if (cm->tx_mode == TX_MODE_SELECT) {
int i, j;
unsigned int ct_8x8p[TX_SIZES - 3][2];
unsigned int ct_16x16p[TX_SIZES - 2][2];
unsigned int ct_32x32p[TX_SIZES - 1][2];
for (i = 0; i < TX_SIZE_CONTEXTS; i++) {
tx_counts_to_branch_counts_8x8(cm->counts.tx.p8x8[i], ct_8x8p);
for (j = 0; j < TX_SIZES - 3; j++)
vp9_cond_prob_diff_update(w, &cm->fc.tx_probs.p8x8[i][j], ct_8x8p[j]);
}
for (i = 0; i < TX_SIZE_CONTEXTS; i++) {
tx_counts_to_branch_counts_16x16(cm->counts.tx.p16x16[i], ct_16x16p);
for (j = 0; j < TX_SIZES - 2; j++)
vp9_cond_prob_diff_update(w, &cm->fc.tx_probs.p16x16[i][j],
ct_16x16p[j]);
}
for (i = 0; i < TX_SIZE_CONTEXTS; i++) {
tx_counts_to_branch_counts_32x32(cm->counts.tx.p32x32[i], ct_32x32p);
for (j = 0; j < TX_SIZES - 1; j++)
vp9_cond_prob_diff_update(w, &cm->fc.tx_probs.p32x32[i][j],
ct_32x32p[j]);
}
}
}
static void write_interp_filter(INTERP_FILTER filter,
struct vp9_write_bit_buffer *wb) {
const int filter_to_literal[] = { 1, 0, 2, 3 };
vp9_wb_write_bit(wb, filter == SWITCHABLE);
if (filter != SWITCHABLE)
vp9_wb_write_literal(wb, filter_to_literal[filter], 2);
}
static void fix_interp_filter(VP9_COMMON *cm) {
if (cm->interp_filter == SWITCHABLE) {
// Check to see if only one of the filters is actually used
int count[SWITCHABLE_FILTERS];
int i, j, c = 0;
for (i = 0; i < SWITCHABLE_FILTERS; ++i) {
count[i] = 0;
for (j = 0; j < SWITCHABLE_FILTER_CONTEXTS; ++j)
count[i] += cm->counts.switchable_interp[j][i];
c += (count[i] > 0);
}
if (c == 1) {
// Only one filter is used. So set the filter at frame level
for (i = 0; i < SWITCHABLE_FILTERS; ++i) {
if (count[i]) {
cm->interp_filter = i;
break;
}
}
}
}
}
static void write_tile_info(const VP9_COMMON *const cm,
struct vp9_write_bit_buffer *wb) {
int min_log2_tile_cols, max_log2_tile_cols, ones;
vp9_get_tile_n_bits(cm->mi_cols, &min_log2_tile_cols, &max_log2_tile_cols);
// columns
ones = cm->log2_tile_cols - min_log2_tile_cols;
while (ones--)
vp9_wb_write_bit(wb, 1);
if (cm->log2_tile_cols < max_log2_tile_cols)
vp9_wb_write_bit(wb, 0);
// rows
vp9_wb_write_bit(wb, cm->log2_tile_rows != 0);
if (cm->log2_tile_rows != 0)
vp9_wb_write_bit(wb, cm->log2_tile_rows != 1);
}
static int get_refresh_mask(VP9_COMP *cpi) {
if (vp9_preserve_existing_gf(cpi)) {
// We have decided to preserve the previously existing golden frame as our
// new ARF frame. However, in the short term we leave it in the GF slot and,
// if we're updating the GF with the current decoded frame, we save it
// instead to the ARF slot.
// Later, in the function vp9_encoder.c:vp9_update_reference_frames() we
// will swap gld_fb_idx and alt_fb_idx to achieve our objective. We do it
// there so that it can be done outside of the recode loop.
// Note: This is highly specific to the use of ARF as a forward reference,
// and this needs to be generalized as other uses are implemented
// (like RTC/temporal scalability).
return (cpi->refresh_last_frame << cpi->lst_fb_idx) |
(cpi->refresh_golden_frame << cpi->alt_fb_idx);
} else {
int arf_idx = cpi->alt_fb_idx;
if ((cpi->oxcf.pass == 2) && cpi->multi_arf_allowed) {
const GF_GROUP *const gf_group = &cpi->twopass.gf_group;
arf_idx = gf_group->arf_update_idx[gf_group->index];
}
return (cpi->refresh_last_frame << cpi->lst_fb_idx) |
(cpi->refresh_golden_frame << cpi->gld_fb_idx) |
(cpi->refresh_alt_ref_frame << arf_idx);
}
}
static size_t encode_tiles(VP9_COMP *cpi, uint8_t *data_ptr) {
VP9_COMMON *const cm = &cpi->common;
vp9_writer residual_bc;
int tile_row, tile_col;
TOKENEXTRA *tok[4][1 << 6], *tok_end;
size_t total_size = 0;
const int tile_cols = 1 << cm->log2_tile_cols;
const int tile_rows = 1 << cm->log2_tile_rows;
vpx_memset(cm->above_seg_context, 0, sizeof(*cm->above_seg_context) *
mi_cols_aligned_to_sb(cm->mi_cols));
tok[0][0] = cpi->tok;
for (tile_row = 0; tile_row < tile_rows; tile_row++) {
if (tile_row)
tok[tile_row][0] = tok[tile_row - 1][tile_cols - 1] +
cpi->tok_count[tile_row - 1][tile_cols - 1];
for (tile_col = 1; tile_col < tile_cols; tile_col++)
tok[tile_row][tile_col] = tok[tile_row][tile_col - 1] +
cpi->tok_count[tile_row][tile_col - 1];
}
for (tile_row = 0; tile_row < tile_rows; tile_row++) {
for (tile_col = 0; tile_col < tile_cols; tile_col++) {
TileInfo tile;
vp9_tile_init(&tile, cm, tile_row, tile_col);
tok_end = tok[tile_row][tile_col] + cpi->tok_count[tile_row][tile_col];
if (tile_col < tile_cols - 1 || tile_row < tile_rows - 1)
vp9_start_encode(&residual_bc, data_ptr + total_size + 4);
else
vp9_start_encode(&residual_bc, data_ptr + total_size);
write_modes(cpi, &tile, &residual_bc, &tok[tile_row][tile_col], tok_end);
assert(tok[tile_row][tile_col] == tok_end);
vp9_stop_encode(&residual_bc);
if (tile_col < tile_cols - 1 || tile_row < tile_rows - 1) {
// size of this tile
mem_put_be32(data_ptr + total_size, residual_bc.pos);
total_size += 4;
}
total_size += residual_bc.pos;
}
}
return total_size;
}
static void write_display_size(const VP9_COMMON *cm,
struct vp9_write_bit_buffer *wb) {
const int scaling_active = cm->width != cm->display_width ||
cm->height != cm->display_height;
vp9_wb_write_bit(wb, scaling_active);
if (scaling_active) {
vp9_wb_write_literal(wb, cm->display_width - 1, 16);
vp9_wb_write_literal(wb, cm->display_height - 1, 16);
}
}
static void write_frame_size(const VP9_COMMON *cm,
struct vp9_write_bit_buffer *wb) {
vp9_wb_write_literal(wb, cm->width - 1, 16);
vp9_wb_write_literal(wb, cm->height - 1, 16);
write_display_size(cm, wb);
}
static void write_frame_size_with_refs(VP9_COMP *cpi,
struct vp9_write_bit_buffer *wb) {
VP9_COMMON *const cm = &cpi->common;
int found = 0;
MV_REFERENCE_FRAME ref_frame;
for (ref_frame = LAST_FRAME; ref_frame <= ALTREF_FRAME; ++ref_frame) {
YV12_BUFFER_CONFIG *cfg = get_ref_frame_buffer(cpi, ref_frame);
found = cm->width == cfg->y_crop_width &&
cm->height == cfg->y_crop_height;
// Set "found" to 0 for temporal svc and for spatial svc key frame
if (cpi->use_svc &&
((cpi->svc.number_temporal_layers > 1 &&
cpi->oxcf.rc_mode == VPX_CBR) ||
(cpi->svc.number_spatial_layers > 1 &&
cpi->svc.layer_context[cpi->svc.spatial_layer_id].is_key_frame) ||
(is_two_pass_svc(cpi) &&
cpi->svc.encode_empty_frame_state == ENCODING &&
cpi->svc.layer_context[0].frames_from_key_frame <
cpi->svc.number_temporal_layers + 1))) {
found = 0;
}
vp9_wb_write_bit(wb, found);
if (found) {
break;
}
}
if (!found) {
vp9_wb_write_literal(wb, cm->width - 1, 16);
vp9_wb_write_literal(wb, cm->height - 1, 16);
}
write_display_size(cm, wb);
}
static void write_sync_code(struct vp9_write_bit_buffer *wb) {
vp9_wb_write_literal(wb, VP9_SYNC_CODE_0, 8);
vp9_wb_write_literal(wb, VP9_SYNC_CODE_1, 8);
vp9_wb_write_literal(wb, VP9_SYNC_CODE_2, 8);
}
static void write_profile(BITSTREAM_PROFILE profile,
struct vp9_write_bit_buffer *wb) {
switch (profile) {
case PROFILE_0:
vp9_wb_write_literal(wb, 0, 2);
break;
case PROFILE_1:
vp9_wb_write_literal(wb, 2, 2);
break;
case PROFILE_2:
vp9_wb_write_literal(wb, 1, 2);
break;
case PROFILE_3:
vp9_wb_write_literal(wb, 6, 3);
break;
default:
assert(0);
}
}
static void write_bitdepth_colorspace_sampling(
VP9_COMMON *const cm, struct vp9_write_bit_buffer *wb) {
if (cm->profile >= PROFILE_2) {
assert(cm->bit_depth > VPX_BITS_8);
vp9_wb_write_bit(wb, cm->bit_depth == VPX_BITS_10 ? 0 : 1);
}
vp9_wb_write_literal(wb, cm->color_space, 3);
if (cm->color_space != SRGB) {
vp9_wb_write_bit(wb, 0); // 0: [16, 235] (i.e. xvYCC), 1: [0, 255]
if (cm->profile == PROFILE_1 || cm->profile == PROFILE_3) {
assert(cm->subsampling_x != 1 || cm->subsampling_y != 1);
vp9_wb_write_bit(wb, cm->subsampling_x);
vp9_wb_write_bit(wb, cm->subsampling_y);
vp9_wb_write_bit(wb, 0); // unused
} else {
assert(cm->subsampling_x == 1 && cm->subsampling_y == 1);
}
} else {
assert(cm->profile == PROFILE_1 || cm->profile == PROFILE_3);
vp9_wb_write_bit(wb, 0); // unused
}
}
static void write_uncompressed_header(VP9_COMP *cpi,
struct vp9_write_bit_buffer *wb) {
VP9_COMMON *const cm = &cpi->common;
vp9_wb_write_literal(wb, VP9_FRAME_MARKER, 2);
write_profile(cm->profile, wb);
vp9_wb_write_bit(wb, 0); // show_existing_frame
vp9_wb_write_bit(wb, cm->frame_type);
vp9_wb_write_bit(wb, cm->show_frame);
vp9_wb_write_bit(wb, cm->error_resilient_mode);
if (cm->frame_type == KEY_FRAME) {
write_sync_code(wb);
write_bitdepth_colorspace_sampling(cm, wb);
write_frame_size(cm, wb);
} else {
// In spatial svc if it's not error_resilient_mode then we need to code all
// visible frames as invisible. But we need to keep the show_frame flag so
// that the publisher could know whether it is supposed to be visible.
// So we will code the show_frame flag as it is. Then code the intra_only
// bit here. This will make the bitstream incompatible. In the player we
// will change to show_frame flag to 0, then add an one byte frame with
// show_existing_frame flag which tells the decoder which frame we want to
// show.
if (!cm->show_frame)
vp9_wb_write_bit(wb, cm->intra_only);
if (!cm->error_resilient_mode)
vp9_wb_write_literal(wb, cm->reset_frame_context, 2);
if (cm->intra_only) {
write_sync_code(wb);
// Note for profile 0, 420 8bpp is assumed.
if (cm->profile > PROFILE_0) {
write_bitdepth_colorspace_sampling(cm, wb);
}
vp9_wb_write_literal(wb, get_refresh_mask(cpi), REF_FRAMES);
write_frame_size(cm, wb);
} else {
MV_REFERENCE_FRAME ref_frame;
vp9_wb_write_literal(wb, get_refresh_mask(cpi), REF_FRAMES);
for (ref_frame = LAST_FRAME; ref_frame <= ALTREF_FRAME; ++ref_frame) {
vp9_wb_write_literal(wb, get_ref_frame_idx(cpi, ref_frame),
REF_FRAMES_LOG2);
vp9_wb_write_bit(wb, cm->ref_frame_sign_bias[ref_frame]);
}
write_frame_size_with_refs(cpi, wb);
vp9_wb_write_bit(wb, cm->allow_high_precision_mv);
fix_interp_filter(cm);
write_interp_filter(cm->interp_filter, wb);
}
}
if (!cm->error_resilient_mode) {
vp9_wb_write_bit(wb, cm->refresh_frame_context);
vp9_wb_write_bit(wb, cm->frame_parallel_decoding_mode);
}
vp9_wb_write_literal(wb, cm->frame_context_idx, FRAME_CONTEXTS_LOG2);
encode_loopfilter(&cm->lf, wb);
encode_quantization(cm, wb);
encode_segmentation(cm, &cpi->mb.e_mbd, wb);
write_tile_info(cm, wb);
}
static size_t write_compressed_header(VP9_COMP *cpi, uint8_t *data) {
VP9_COMMON *const cm = &cpi->common;
MACROBLOCKD *const xd = &cpi->mb.e_mbd;
FRAME_CONTEXT *const fc = &cm->fc;
vp9_writer header_bc;
vp9_start_encode(&header_bc, data);
if (xd->lossless)
cm->tx_mode = ONLY_4X4;
else
encode_txfm_probs(cm, &header_bc);
update_coef_probs(cpi, &header_bc);
update_skip_probs(cm, &header_bc);
if (!frame_is_intra_only(cm)) {
int i;
for (i = 0; i < INTER_MODE_CONTEXTS; ++i)
prob_diff_update(vp9_inter_mode_tree, cm->fc.inter_mode_probs[i],
cm->counts.inter_mode[i], INTER_MODES, &header_bc);
vp9_zero(cm->counts.inter_mode);
if (cm->interp_filter == SWITCHABLE)
update_switchable_interp_probs(cm, &header_bc);
for (i = 0; i < INTRA_INTER_CONTEXTS; i++)
vp9_cond_prob_diff_update(&header_bc, &fc->intra_inter_prob[i],
cm->counts.intra_inter[i]);
if (cm->allow_comp_inter_inter) {
const int use_compound_pred = cm->reference_mode != SINGLE_REFERENCE;
const int use_hybrid_pred = cm->reference_mode == REFERENCE_MODE_SELECT;
vp9_write_bit(&header_bc, use_compound_pred);
if (use_compound_pred) {
vp9_write_bit(&header_bc, use_hybrid_pred);
if (use_hybrid_pred)
for (i = 0; i < COMP_INTER_CONTEXTS; i++)
vp9_cond_prob_diff_update(&header_bc, &fc->comp_inter_prob[i],
cm->counts.comp_inter[i]);
}
}
if (cm->reference_mode != COMPOUND_REFERENCE) {
for (i = 0; i < REF_CONTEXTS; i++) {
vp9_cond_prob_diff_update(&header_bc, &fc->single_ref_prob[i][0],
cm->counts.single_ref[i][0]);
vp9_cond_prob_diff_update(&header_bc, &fc->single_ref_prob[i][1],
cm->counts.single_ref[i][1]);
}
}
if (cm->reference_mode != SINGLE_REFERENCE)
for (i = 0; i < REF_CONTEXTS; i++)
vp9_cond_prob_diff_update(&header_bc, &fc->comp_ref_prob[i],
cm->counts.comp_ref[i]);
for (i = 0; i < BLOCK_SIZE_GROUPS; ++i)
prob_diff_update(vp9_intra_mode_tree, cm->fc.y_mode_prob[i],
cm->counts.y_mode[i], INTRA_MODES, &header_bc);
for (i = 0; i < PARTITION_CONTEXTS; ++i)
prob_diff_update(vp9_partition_tree, fc->partition_prob[i],
cm->counts.partition[i], PARTITION_TYPES, &header_bc);
vp9_write_nmv_probs(cm, cm->allow_high_precision_mv, &header_bc);
}
vp9_stop_encode(&header_bc);
assert(header_bc.pos <= 0xffff);
return header_bc.pos;
}
void vp9_pack_bitstream(VP9_COMP *cpi, uint8_t *dest, size_t *size) {
uint8_t *data = dest;
size_t first_part_size, uncompressed_hdr_size;
struct vp9_write_bit_buffer wb = {data, 0};
struct vp9_write_bit_buffer saved_wb;
write_uncompressed_header(cpi, &wb);
saved_wb = wb;
vp9_wb_write_literal(&wb, 0, 16); // don't know in advance first part. size
uncompressed_hdr_size = vp9_wb_bytes_written(&wb);
data += uncompressed_hdr_size;
vp9_clear_system_state();
first_part_size = write_compressed_header(cpi, data);
data += first_part_size;
// TODO(jbb): Figure out what to do if first_part_size > 16 bits.
vp9_wb_write_literal(&saved_wb, (int)first_part_size, 16);
data += encode_tiles(cpi, data);
*size = data - dest;
}