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 */
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
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 */
47 const uint32_t *
quant) {
49 int8_t ac;
51
52 // block not coded
53 if (dc == 255)
54 return 0;
55
56 // number of non-zero coefficients
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) {
68 if (ac == -2)
69 break; // continue with more bits
71 }
72
73 // 4 bits per coefficient
76 return -1;
77 while (coeff) {
79 if (ac == -8)
80 break; // continue with more bits
82 }
83
84 // 8 bits per coefficient
87 return -1;
88 while (coeff) {
91 }
92
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 */
109 int w = c->
w / 16, h = c->
h / 16;
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)
125 y1 += 8;
127 y1 += 8;
129 y2 += 8;
131 y2 += 8;
133 u += 8;
136 }
141 }
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 */
158 const uint32_t *lquant, const uint32_t *cquant) {
159 int i;
161 for (i = 0; i < 64; 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
170 }
173 }