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/avassert.h"
28 #include "libavutil/bswap.h"
29 #include "libavutil/common.h"
30
31 #include "gif.h"
32 #include "parser.h"
33
34 typedef enum GIFParseStates {
35 GIF_HEADER = 1,
36 GIF_EXTENSION,
37 GIF_EXTENSION_BLOCK,
38 GIF_IMAGE,
39 GIF_IMAGE_BLOCK,
40 } gif_states;
41
42 typedef struct GIFParseContext {
43 ParseContext pc;
44 unsigned found_sig;
45 int found_start;
46 int found_end;
47 int index;
48 int state;
49 int gct_flag;
50 int gct_size;
51 int block_size;
52 int etype;
53 int delay;
54 } GIFParseContext;
55
gif_find_frame_end(GIFParseContext * g,const uint8_t * buf,int buf_size,void * logctx)56 static int gif_find_frame_end(GIFParseContext *g, const uint8_t *buf,
57 int buf_size, void *logctx)
58 {
59 int index, next = END_NOT_FOUND;
60
61 for (index = 0; index < buf_size; index++) {
62 if (!g->state) {
63 if (!memcmp(buf + index, gif87a_sig, 6) ||
64 !memcmp(buf + index, gif89a_sig, 6)) {
65 g->state = GIF_HEADER;
66 g->found_sig++;
67 } else if (buf[index] == GIF_EXTENSION_INTRODUCER) {
68 g->state = GIF_EXTENSION;
69 g->found_start = 1;
70 } else if (buf[index] == GIF_IMAGE_SEPARATOR) {
71 g->state = GIF_IMAGE;
72 } else if (buf[index] == GIF_TRAILER) {
73 g->state = 0;
74 g->found_end = 1;
75 g->found_sig = 0;
76 } else {
77 g->found_sig = 0;
78 }
79 }
80
81 if (g->state == GIF_HEADER) {
82 if (g->index == 10) {
83 g->gct_flag = !!(buf[index] & 0x80);
84 g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));
85 }
86 if (g->index >= 12 + g->gct_flag * g->gct_size) {
87 g->state = 0;
88 g->index = 0;
89 g->gct_flag = 0;
90 g->gct_size = 0;
91 continue;
92 }
93 g->index++;
94 } else if (g->state == GIF_EXTENSION) {
95 if (g->found_start && g->found_end && g->found_sig) {
96 next = index;
97 g->found_start = 0;
98 g->found_end = 0;
99 g->index = 0;
100 g->gct_flag = 0;
101 g->gct_size = 0;
102 g->state = 0;
103 break;
104 }
105 if (g->index == 1) {
106 g->etype = buf[index];
107 }
108 if (g->index >= 2) {
109 g->block_size = buf[index];
110 g->index = 0;
111 g->state = GIF_EXTENSION_BLOCK;
112 continue;
113 }
114 g->index++;
115 } else if (g->state == GIF_IMAGE_BLOCK) {
116 if (!g->index)
117 g->block_size = buf[index];
118 if (g->index >= g->block_size) {
119 g->index = 0;
120 if (!g->block_size) {
121 g->state = 0;
122 g->found_end = 1;
123 }
124 continue;
125 }
126 g->index++;
127 } else if (g->state == GIF_EXTENSION_BLOCK) {
128 if (g->etype == GIF_GCE_EXT_LABEL) {
129 if (g->index == 0)
130 g->delay = 0;
131 if (g->index >= 1 && g->index <= 2) {
132 g->delay |= buf[index] << (8 * (g->index - 1));
133 }
134 }
135 if (g->index >= g->block_size) {
136 g->block_size = buf[index];
137 g->index = 0;
138 if (!g->block_size)
139 g->state = 0;
140 continue;
141 }
142 g->index++;
143 } else if (g->state == GIF_IMAGE) {
144 if (g->index == 8) {
145 g->gct_flag = !!(buf[index] & 0x80);
146 g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));
147 }
148 if (g->index >= 10 + g->gct_flag * g->gct_size) {
149 g->state = GIF_IMAGE_BLOCK;
150 g->index = 0;
151 g->gct_flag = 0;
152 g->gct_size = 0;
153 continue;
154 }
155 g->index++;
156 }
157 }
158
159 return next;
160 }
161
gif_parse(AVCodecParserContext * s,AVCodecContext * avctx,const uint8_t ** poutbuf,int * poutbuf_size,const uint8_t * buf,int buf_size)162 static int gif_parse(AVCodecParserContext *s, AVCodecContext *avctx,
163 const uint8_t **poutbuf, int *poutbuf_size,
164 const uint8_t *buf, int buf_size)
165 {
166 GIFParseContext *g = s->priv_data;
167 int next;
168
169 next = gif_find_frame_end(g, buf, buf_size, avctx);
170 if (ff_combine_frame(&g->pc, next, &buf, &buf_size) < 0) {
171 *poutbuf = NULL;
172 *poutbuf_size = 0;
173 return buf_size;
174 }
175
176 s->duration = g->delay;
177
178 *poutbuf = buf;
179 *poutbuf_size = buf_size;
180 return next;
181 }
182
183 AVCodecParser ff_gif_parser = {
184 .codec_ids = { AV_CODEC_ID_GIF },
185 .priv_data_size = sizeof(GIFParseContext),
186 .parser_parse = gif_parse,
187 .parser_close = ff_parse_close,
188 };
189