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/*
* RTJpeg decoding functions
* Copyright (c) 2006 Reimar Doeffinger
*
* This file is part of FFmpeg.
*
* FFmpeg 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 2.1 of the License, or (at your option) any later version.
*
* FFmpeg 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 FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "libavutil/common.h"
#include "get_bits.h"
#include "dsputil.h"
#include "rtjpeg.h"
#define PUT_COEFF(c) \
i = scan[coeff--]; \
block[i] = (c) * quant[i];
/// aligns the bitstream to the given power of two
#define ALIGN(a) \
n = (-get_bits_count(gb)) & (a - 1); \
if (n) {skip_bits(gb, n);}
/**
* @brief read one block from stream
* @param gb contains stream data
* @param block where data is written to
* @param scan array containing the mapping stream address -> block position
* @param quant quantization factors
* @return 0 means the block is not coded, < 0 means an error occurred.
*
* Note: GetBitContext is used to make the code simpler, since all data is
* aligned this could be done faster in a different way, e.g. as it is done
* in MPlayer libmpcodecs/native/rtjpegn.c.
*/
static inline int get_block(GetBitContext *gb, DCTELEM *block, const uint8_t *scan,
const uint32_t *quant) {
int coeff, i, n;
int8_t ac;
uint8_t dc = get_bits(gb, 8);
// block not coded
if (dc == 255)
return 0;
// number of non-zero coefficients
coeff = get_bits(gb, 6);
if (get_bits_left(gb) < (coeff << 1))
return -1;
// normally we would only need to clear the (63 - coeff) last values,
// but since we do not know where they are we just clear the whole block
memset(block, 0, 64 * sizeof(DCTELEM));
// 2 bits per coefficient
while (coeff) {
ac = get_sbits(gb, 2);
if (ac == -2)
break; // continue with more bits
PUT_COEFF(ac);
}
// 4 bits per coefficient
ALIGN(4);
if (get_bits_left(gb) < (coeff << 2))
return -1;
while (coeff) {
ac = get_sbits(gb, 4);
if (ac == -8)
break; // continue with more bits
PUT_COEFF(ac);
}
// 8 bits per coefficient
ALIGN(8);
if (get_bits_left(gb) < (coeff << 3))
return -1;
while (coeff) {
ac = get_sbits(gb, 8);
PUT_COEFF(ac);
}
PUT_COEFF(dc);
return 1;
}
/**
* @brief decode one rtjpeg YUV420 frame
* @param c context, must be initialized via ff_rtjpeg_decode_init
* @param f AVFrame to place decoded frame into. If parts of the frame
* are not coded they are left unchanged, so consider initializing it
* @param buf buffer containing input data
* @param buf_size length of input data in bytes
* @return number of bytes consumed from the input buffer
*/
int ff_rtjpeg_decode_frame_yuv420(RTJpegContext *c, AVFrame *f,
const uint8_t *buf, int buf_size) {
GetBitContext gb;
int w = c->w / 16, h = c->h / 16;
int x, y;
uint8_t *y1 = f->data[0], *y2 = f->data[0] + 8 * f->linesize[0];
uint8_t *u = f->data[1], *v = f->data[2];
init_get_bits(&gb, buf, buf_size * 8);
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
#define BLOCK(quant, dst, stride) do { \
int res = get_block(&gb, block, c->scan, quant); \
if (res < 0) \
return res; \
if (res > 0) \
c->dsp->idct_put(dst, stride, block); \
} while (0)
DCTELEM *block = c->block;
BLOCK(c->lquant, y1, f->linesize[0]);
y1 += 8;
BLOCK(c->lquant, y1, f->linesize[0]);
y1 += 8;
BLOCK(c->lquant, y2, f->linesize[0]);
y2 += 8;
BLOCK(c->lquant, y2, f->linesize[0]);
y2 += 8;
BLOCK(c->cquant, u, f->linesize[1]);
u += 8;
BLOCK(c->cquant, v, f->linesize[2]);
v += 8;
}
y1 += 2 * 8 * (f->linesize[0] - w);
y2 += 2 * 8 * (f->linesize[0] - w);
u += 8 * (f->linesize[1] - w);
v += 8 * (f->linesize[2] - w);
}
return get_bits_count(&gb) / 8;
}
/**
* @brief initialize an RTJpegContext, may be called multiple times
* @param c context to initialize
* @param dsp specifies the idct to use for decoding
* @param width width of image, will be rounded down to the nearest multiple
* of 16 for decoding
* @param height height of image, will be rounded down to the nearest multiple
* of 16 for decoding
* @param lquant luma quantization table to use
* @param cquant chroma quantization table to use
*/
void ff_rtjpeg_decode_init(RTJpegContext *c, DSPContext *dsp,
int width, int height,
const uint32_t *lquant, const uint32_t *cquant) {
int i;
c->dsp = dsp;
for (i = 0; i < 64; i++) {
int z = ff_zigzag_direct[i];
int p = c->dsp->idct_permutation[i];
z = ((z << 3) | (z >> 3)) & 63; // rtjpeg uses a transposed variant
// permute the scan and quantization tables for the chosen idct
c->scan[i] = c->dsp->idct_permutation[z];
c->lquant[p] = lquant[i];
c->cquant[p] = cquant[i];
}
c->w = width;
c->h = height;
}
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