1 /*
2 * GIF parser
3 * Copyright (c) 2018 Paul B Mahol
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
22 /**
23 * @file
24 * GIF parser
25 */
26
27 #include "libavutil/bswap.h"
28 #include "libavutil/common.h"
29
30 #include "gif.h"
31 #include "parser.h"
32
33 typedef enum GIFParseStates {
34 GIF_HEADER = 1,
35 GIF_EXTENSION,
36 GIF_EXTENSION_BLOCK,
37 GIF_IMAGE,
38 GIF_IMAGE_BLOCK,
39 } gif_states;
40
41 typedef struct GIFParseContext {
42 ParseContext pc;
43 unsigned found_sig;
44 int found_start;
45 int found_end;
46 int index;
47 int state;
48 int gct_flag;
49 int gct_size;
50 int block_size;
51 int etype;
52 int delay;
53 } GIFParseContext;
54
gif_find_frame_end(GIFParseContext *g, const uint8_t *buf, int buf_size, void *logctx)55 static int gif_find_frame_end(GIFParseContext *g, const uint8_t *buf,
56 int buf_size, void *logctx)
57 {
58 int index, next = END_NOT_FOUND;
59
60 for (index = 0; index < buf_size; index++) {
61 if (!g->state) {
62 if (!memcmp(buf + index, gif87a_sig, 6) ||
63 !memcmp(buf + index, gif89a_sig, 6)) {
64 g->state = GIF_HEADER;
65 g->found_sig++;
66 } else if (buf[index] == GIF_EXTENSION_INTRODUCER) {
67 g->state = GIF_EXTENSION;
68 g->found_start = 1;
69 } else if (buf[index] == GIF_IMAGE_SEPARATOR) {
70 g->state = GIF_IMAGE;
71 } else if (buf[index] == GIF_TRAILER) {
72 g->state = 0;
73 g->found_end = 1;
74 g->found_sig = 0;
75 } else {
76 g->found_sig = 0;
77 }
78 }
79
80 if (g->state == GIF_HEADER) {
81 if (g->index == 10) {
82 g->gct_flag = !!(buf[index] & 0x80);
83 g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));
84 }
85 if (g->index >= 12 + g->gct_flag * g->gct_size) {
86 g->state = 0;
87 g->index = 0;
88 g->gct_flag = 0;
89 g->gct_size = 0;
90 continue;
91 }
92 g->index++;
93 } else if (g->state == GIF_EXTENSION) {
94 if (g->found_start && g->found_end && g->found_sig) {
95 next = index;
96 g->found_start = 0;
97 g->found_end = 0;
98 g->index = 0;
99 g->gct_flag = 0;
100 g->gct_size = 0;
101 g->state = 0;
102 break;
103 }
104 if (g->index == 1) {
105 g->etype = buf[index];
106 }
107 if (g->index >= 2) {
108 g->block_size = buf[index];
109 g->index = 0;
110 g->state = GIF_EXTENSION_BLOCK;
111 continue;
112 }
113 g->index++;
114 } else if (g->state == GIF_IMAGE_BLOCK) {
115 if (!g->index)
116 g->block_size = buf[index];
117 if (g->index >= g->block_size) {
118 g->index = 0;
119 if (!g->block_size) {
120 g->state = 0;
121 g->found_end = 1;
122 }
123 continue;
124 }
125 g->index++;
126 } else if (g->state == GIF_EXTENSION_BLOCK) {
127 if (g->etype == GIF_GCE_EXT_LABEL) {
128 if (g->index == 0)
129 g->delay = 0;
130 if (g->index >= 1 && g->index <= 2) {
131 g->delay |= buf[index] << (8 * (g->index - 1));
132 }
133 }
134 if (g->index >= g->block_size) {
135 g->block_size = buf[index];
136 g->index = 0;
137 if (!g->block_size)
138 g->state = 0;
139 continue;
140 }
141 g->index++;
142 } else if (g->state == GIF_IMAGE) {
143 if (g->index == 8) {
144 g->gct_flag = !!(buf[index] & 0x80);
145 g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));
146 }
147 if (g->index >= 10 + g->gct_flag * g->gct_size) {
148 g->state = GIF_IMAGE_BLOCK;
149 g->index = 0;
150 g->gct_flag = 0;
151 g->gct_size = 0;
152 continue;
153 }
154 g->index++;
155 }
156 }
157
158 return next;
159 }
160
gif_parse(AVCodecParserContext *s, AVCodecContext *avctx, const uint8_t **poutbuf, int *poutbuf_size, const uint8_t *buf, int buf_size)161 static int gif_parse(AVCodecParserContext *s, AVCodecContext *avctx,
162 const uint8_t **poutbuf, int *poutbuf_size,
163 const uint8_t *buf, int buf_size)
164 {
165 GIFParseContext *g = s->priv_data;
166 int next;
167
168 next = gif_find_frame_end(g, buf, buf_size, avctx);
169 if (ff_combine_frame(&g->pc, next, &buf, &buf_size) < 0) {
170 *poutbuf = NULL;
171 *poutbuf_size = 0;
172 return buf_size;
173 }
174
175 s->duration = g->delay;
176
177 *poutbuf = buf;
178 *poutbuf_size = buf_size;
179 return next;
180 }
181
182 const AVCodecParser ff_gif_parser = {
183 .codec_ids = { AV_CODEC_ID_GIF },
184 .priv_data_size = sizeof(GIFParseContext),
185 .parser_parse = gif_parse,
186 .parser_close = ff_parse_close,
187 };
188