2 * RTJpeg decoding functions
3 * Copyright (c) 2006 Reimar Doeffinger
5 * This file is part of Libav.
7 * Libav 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.
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13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with Libav; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21 #include "libavutil/common.h"
26 #define PUT_COEFF(c) \
28 block[i] = (c) * quant[i];
30 /// aligns the bitstream to the given power of two
32 n = (-get_bits_count(gb)) & (a - 1); \
33 if (n) {skip_bits(gb, n);}
36 * @brief read one block from stream
37 * @param gb contains stream data
38 * @param block where data is written to
39 * @param scan array containing the mapping stream address -> block position
40 * @param quant quantization factors
41 * @return 0 means the block is not coded, < 0 means an error occurred.
43 * Note: GetBitContext is used to make the code simpler, since all data is
44 * aligned this could be done faster in a different way, e.g. as it is done
45 * in MPlayer libmpcodecs/native/rtjpegn.c.
47 static inline int get_block(GetBitContext *gb, DCTELEM *block, const uint8_t *scan,
48 const uint32_t *quant) {
51 uint8_t dc = get_bits(gb, 8);
57 // number of non-zero coefficients
58 coeff = get_bits(gb, 6);
59 if (get_bits_left(gb) < (coeff << 1))
62 // normally we would only need to clear the (63 - coeff) last values,
63 // but since we do not know where they are we just clear the whole block
64 memset(block, 0, 64 * sizeof(DCTELEM));
66 // 2 bits per coefficient
68 ac = get_sbits(gb, 2);
70 break; // continue with more bits
74 // 4 bits per coefficient
76 if (get_bits_left(gb) < (coeff << 2))
79 ac = get_sbits(gb, 4);
81 break; // continue with more bits
85 // 8 bits per coefficient
87 if (get_bits_left(gb) < (coeff << 3))
90 ac = get_sbits(gb, 8);
99 * @brief decode one rtjpeg YUV420 frame
100 * @param c context, must be initialized via ff_rtjpeg_decode_init
101 * @param f AVFrame to place decoded frame into. If parts of the frame
102 * are not coded they are left unchanged, so consider initializing it
103 * @param buf buffer containing input data
104 * @param buf_size length of input data in bytes
105 * @return number of bytes consumed from the input buffer
107 int ff_rtjpeg_decode_frame_yuv420(RTJpegContext *c, AVFrame *f,
108 const uint8_t *buf, int buf_size) {
110 int w = c->w / 16, h = c->h / 16;
112 uint8_t *y1 = f->data[0], *y2 = f->data[0] + 8 * f->linesize[0];
113 uint8_t *u = f->data[1], *v = f->data[2];
114 init_get_bits(&gb, buf, buf_size * 8);
115 for (y = 0; y < h; y++) {
116 for (x = 0; x < w; x++) {
117 #define BLOCK(quant, dst, stride) do { \
118 int res = get_block(&gb, block, c->scan, quant); \
122 c->dsp->idct_put(dst, stride, block); \
124 DCTELEM *block = c->block;
125 BLOCK(c->lquant, y1, f->linesize[0]);
127 BLOCK(c->lquant, y1, f->linesize[0]);
129 BLOCK(c->lquant, y2, f->linesize[0]);
131 BLOCK(c->lquant, y2, f->linesize[0]);
133 BLOCK(c->cquant, u, f->linesize[1]);
135 BLOCK(c->cquant, v, f->linesize[2]);
138 y1 += 2 * 8 * (f->linesize[0] - w);
139 y2 += 2 * 8 * (f->linesize[0] - w);
140 u += 8 * (f->linesize[1] - w);
141 v += 8 * (f->linesize[2] - w);
143 return get_bits_count(&gb) / 8;
147 * @brief initialize an RTJpegContext, may be called multiple times
148 * @param c context to initialize
149 * @param dsp specifies the idct to use for decoding
150 * @param width width of image, will be rounded down to the nearest multiple
152 * @param height height of image, will be rounded down to the nearest multiple
154 * @param lquant luma quantization table to use
155 * @param cquant chroma quantization table to use
157 void ff_rtjpeg_decode_init(RTJpegContext *c, DSPContext *dsp,
158 int width, int height,
159 const uint32_t *lquant, const uint32_t *cquant) {
162 for (i = 0; i < 64; i++) {
163 int z = ff_zigzag_direct[i];
164 int p = c->dsp->idct_permutation[i];
165 z = ((z << 3) | (z >> 3)) & 63; // rtjpeg uses a transposed variant
167 // permute the scan and quantization tables for the chosen idct
168 c->scan[i] = c->dsp->idct_permutation[z];
169 c->lquant[p] = lquant[i];
170 c->cquant[p] = cquant[i];