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rtjpeg.c
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1 /*
2  * RTJpeg decoding functions
3  * Copyright (c) 2006 Reimar Doeffinger
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 #include "libavutil/common.h"
22 #include "get_bits.h"
23 #include "rtjpeg.h"
24 
25 #define PUT_COEFF(c) \
26  i = scan[coeff--]; \
27  block[i] = (c) * quant[i];
28 
29 /// aligns the bitstream to the given power of two
30 #define ALIGN(a) \
31  n = (-get_bits_count(gb)) & (a - 1); \
32  if (n) {skip_bits(gb, n);}
33 
34 /**
35  * @brief read one block from stream
36  * @param gb contains stream data
37  * @param block where data is written to
38  * @param scan array containing the mapping stream address -> block position
39  * @param quant quantization factors
40  * @return 0 means the block is not coded, < 0 means an error occurred.
41  *
42  * Note: GetBitContext is used to make the code simpler, since all data is
43  * aligned this could be done faster in a different way, e.g. as it is done
44  * in MPlayer libmpcodecs/native/rtjpegn.c.
45  */
46 static inline int get_block(GetBitContext *gb, int16_t *block, const uint8_t *scan,
47  const uint32_t *quant) {
48  int coeff, i, n;
49  int8_t ac;
50  uint8_t dc = get_bits(gb, 8);
51 
52  // block not coded
53  if (dc == 255)
54  return 0;
55 
56  // number of non-zero coefficients
57  coeff = get_bits(gb, 6);
58  if (get_bits_left(gb) < (coeff << 1))
59  return -1;
60 
61  // normally we would only need to clear the (63 - coeff) last values,
62  // but since we do not know where they are we just clear the whole block
63  memset(block, 0, 64 * sizeof(int16_t));
64 
65  // 2 bits per coefficient
66  while (coeff) {
67  ac = get_sbits(gb, 2);
68  if (ac == -2)
69  break; // continue with more bits
70  PUT_COEFF(ac);
71  }
72 
73  // 4 bits per coefficient
74  ALIGN(4);
75  if (get_bits_left(gb) < (coeff << 2))
76  return -1;
77  while (coeff) {
78  ac = get_sbits(gb, 4);
79  if (ac == -8)
80  break; // continue with more bits
81  PUT_COEFF(ac);
82  }
83 
84  // 8 bits per coefficient
85  ALIGN(8);
86  if (get_bits_left(gb) < (coeff << 3))
87  return -1;
88  while (coeff) {
89  ac = get_sbits(gb, 8);
90  PUT_COEFF(ac);
91  }
92 
93  PUT_COEFF(dc);
94  return 1;
95 }
96 
97 /**
98  * @brief decode one rtjpeg YUV420 frame
99  * @param c context, must be initialized via ff_rtjpeg_decode_init
100  * @param f AVFrame to place decoded frame into. If parts of the frame
101  * are not coded they are left unchanged, so consider initializing it
102  * @param buf buffer containing input data
103  * @param buf_size length of input data in bytes
104  * @return number of bytes consumed from the input buffer
105  */
107  const uint8_t *buf, int buf_size) {
108  GetBitContext gb;
109  int w = c->w / 16, h = c->h / 16;
110  int x, y;
111  uint8_t *y1 = f->data[0], *y2 = f->data[0] + 8 * f->linesize[0];
112  uint8_t *u = f->data[1], *v = f->data[2];
113  init_get_bits(&gb, buf, buf_size * 8);
114  for (y = 0; y < h; y++) {
115  for (x = 0; x < w; x++) {
116 #define BLOCK(quant, dst, stride) do { \
117  int res = get_block(&gb, block, c->scan, quant); \
118  if (res < 0) \
119  return res; \
120  if (res > 0) \
121  c->dsp->idct_put(dst, stride, block); \
122 } while (0)
123  int16_t *block = c->block;
124  BLOCK(c->lquant, y1, f->linesize[0]);
125  y1 += 8;
126  BLOCK(c->lquant, y1, f->linesize[0]);
127  y1 += 8;
128  BLOCK(c->lquant, y2, f->linesize[0]);
129  y2 += 8;
130  BLOCK(c->lquant, y2, f->linesize[0]);
131  y2 += 8;
132  BLOCK(c->cquant, u, f->linesize[1]);
133  u += 8;
134  BLOCK(c->cquant, v, f->linesize[2]);
135  v += 8;
136  }
137  y1 += 2 * 8 * (f->linesize[0] - w);
138  y2 += 2 * 8 * (f->linesize[0] - w);
139  u += 8 * (f->linesize[1] - w);
140  v += 8 * (f->linesize[2] - w);
141  }
142  return get_bits_count(&gb) / 8;
143 }
144 
145 /**
146  * @brief initialize an RTJpegContext, may be called multiple times
147  * @param c context to initialize
148  * @param dsp specifies the idct to use for decoding
149  * @param width width of image, will be rounded down to the nearest multiple
150  * of 16 for decoding
151  * @param height height of image, will be rounded down to the nearest multiple
152  * of 16 for decoding
153  * @param lquant luma quantization table to use
154  * @param cquant chroma quantization table to use
155  */
157  int width, int height,
158  const uint32_t *lquant, const uint32_t *cquant) {
159  int i;
160  c->dsp = dsp;
161  for (i = 0; i < 64; i++) {
162  int z = ff_zigzag_direct[i];
163  int p = c->dsp->idct_permutation[i];
164  z = ((z << 3) | (z >> 3)) & 63; // rtjpeg uses a transposed variant
165 
166  // permute the scan and quantization tables for the chosen idct
167  c->scan[i] = c->dsp->idct_permutation[z];
168  c->lquant[p] = lquant[i];
169  c->cquant[p] = cquant[i];
170  }
171  c->w = width;
172  c->h = height;
173 }