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/**
* Flake: FLAC audio encoder
* Copyright (c) 2006 Justin Ruggles
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "common.h"
#include "flake.h"
#include "vbs.h"
#include "encode.h"
#define SPLIT_THRESHOLD 100
/**
* Split single frame into smaller frames using predictability comparison.
* This algorithm computes predictablity estimates for sections of the frame
* by first summing the absolute value of fixed 2nd order residual, averaged
* across all channels. The predictability is compared between adjacent
* sections to determine if they should be merged based on a fixed comparison
* threshold.
*/
static void
split_frame_v1(int16_t *samples, int channels, int block_size,
int *frames, int sizes[8])
{
int i, ch, j;
int n = block_size >> 3;
int64_t res[8];
int layout[8];
int16_t *sptr, *sptr0, *sptr1, *sptr2;
// calculate absolute sum of 2nd order residual
for(i=0; i<8; i++) {
sptr = &samples[i*n*channels];
res[i] = 0;
for(ch=0; ch<channels; ch++) {
sptr0 = sptr + (2*channels+ch);
sptr1 = sptr0 - channels;
sptr2 = sptr1 - channels;
for(j=2; j<n; j++) {
res[i] += abs((*sptr0) - 2*(*sptr1) + (*sptr2));
sptr0 += channels;
sptr1 += channels;
sptr2 += channels;
}
}
res[i] /= channels;
res[i]++;
}
// determine frame layout
memset(layout, 0, 8 * sizeof(int));
layout[0] = 1;
for(i=0; i<7; i++) {
if(abs(res[i]-res[i+1])*200 / res[i] > SPLIT_THRESHOLD) {
layout[i+1] = 1;
}
}
// generate frame count and frame sizes from layout
frames[0] = 0;
memset(sizes, 0, 8 * sizeof(int));
for(i=0; i<8; i++) {
if(layout[i]) {
frames[0]++;
}
sizes[frames[0]-1] += n;
}
}
static void
split_frame_v2(FlakeContext *s, int16_t *samples, int *frames, int sizes[8])
{
int fsizes[4][8];
int layout[8];
int i, j, n, ch;
FlacEncodeContext *ctx = (FlacEncodeContext *) s->private_ctx;
ch = ctx->channels;
// encode for each level to get sizes
for(i=0; i<4; i++) {
int levels, bs;
levels = (1<<i);
s->params.block_size /= levels;
bs = s->params.block_size;
for(j=0; j<levels; j++) {
fsizes[i][j] = encode_frame(s, NULL, &samples[bs*j*ch]);
}
s->params.block_size *= levels;
}
// initialize layout
for(i=0; i<8; i++) layout[i] = 1;
// level 3 merge
if(fsizes[2][0] < (fsizes[3][0]+fsizes[3][1])) {
layout[1] = 0;
}
if(fsizes[2][1] < (fsizes[3][2]+fsizes[3][3])) {
layout[3] = 0;
}
if(fsizes[2][2] < (fsizes[3][4]+fsizes[3][5])) {
layout[5] = 0;
}
if(fsizes[2][3] < (fsizes[3][6]+fsizes[3][7])) {
layout[7] = 0;
}
// level 2 merge
if(layout[1] == 0 && layout[3] == 0) {
if(fsizes[1][0] < (fsizes[2][0]+fsizes[2][1])) {
layout[2] = 0;
}
}
if(layout[5] == 0 && layout[7] == 0) {
if(fsizes[1][1] < (fsizes[2][2]+fsizes[2][3])) {
layout[6] = 0;
}
}
// level 1 merge
if(layout[2] == 0 && layout[6] == 0) {
if(fsizes[0][0] < (fsizes[1][0]+fsizes[1][1])) {
layout[4] = 0;
}
}
// generate frame count and frame sizes from layout
n = s->params.block_size >> 3;
frames[0] = 0;
memset(sizes, 0, 8 * sizeof(int));
for(i=0; i<8; i++) {
if(layout[i]) {
frames[0]++;
}
sizes[frames[0]-1] += n;
}
}
int
encode_frame_vbs(FlakeContext *s, uint8_t *frame_buffer, int16_t *samples)
{
int fs;
int frames;
int sizes[8];
FlacEncodeContext *ctx;
ctx = (FlacEncodeContext *) s->private_ctx;
switch(ctx->params.variable_block_size) {
case 1: split_frame_v1(samples, s->channels, s->params.block_size, &frames, sizes);
break;
case 2: split_frame_v2(s, samples, &frames, sizes);
break;
default: frames = 1;
break;
}
if(frames > 1) {
int i, fpos, spos, bs;
fpos = 0;
spos = 0;
bs = s->params.block_size;
for(i=0; i<frames; i++) {
s->params.block_size = sizes[i];
fs = encode_frame(s, &frame_buffer[fpos], &samples[spos*ctx->channels]);
if(fs < 0) return -1;
fpos += fs;
spos += sizes[i];
}
s->params.block_size = bs;
assert(spos == bs);
return fpos;
}
fs = encode_frame(s, frame_buffer, samples);
return fs;
}
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