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gifdec.c
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1 /*
2  * GIF demuxer
3  * Copyright (c) 2012 Vitaliy E Sugrobov
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 demuxer.
25  */
26 
27 #include "avformat.h"
28 #include "libavutil/intreadwrite.h"
29 #include "libavutil/opt.h"
30 #include "internal.h"
31 #include "libavcodec/gif.h"
32 
33 typedef struct GIFDemuxContext {
34  const AVClass *class;
35  /**
36  * Time span in hundredths of second before
37  * the next frame should be drawn on screen.
38  */
39  int delay;
40  /**
41  * Minimum allowed delay between frames in hundredths of
42  * second. Values below this threshold considered to be
43  * invalid and set to value of default_delay.
44  */
45  int min_delay;
47 
48  /**
49  * loop options
50  */
55 
56 /**
57  * Major web browsers display gifs at ~10-15fps when rate
58  * is not explicitly set or have too low values. We assume default rate to be 10.
59  * Default delay = 100hundredths of second / 10fps = 10hos per frame.
60  */
61 #define GIF_DEFAULT_DELAY 10
62 /**
63  * By default delay values less than this threshold considered to be invalid.
64  */
65 #define GIF_MIN_DELAY 2
66 
67 static int gif_probe(AVProbeData *p)
68 {
69  /* check magick */
70  if (memcmp(p->buf, gif87a_sig, 6) && memcmp(p->buf, gif89a_sig, 6))
71  return 0;
72 
73  /* width or height contains zero? */
74  if (!AV_RL16(&p->buf[6]) || !AV_RL16(&p->buf[8]))
75  return 0;
76 
77  return AVPROBE_SCORE_MAX;
78 }
79 
80 static int resync(AVIOContext *pb)
81 {
82  int i;
83  for (i = 0; i < 6; i++) {
84  int b = avio_r8(pb);
85  if (b != gif87a_sig[i] && b != gif89a_sig[i])
86  i = -(b != 'G');
87  if (url_feof(pb))
88  return AVERROR_EOF;
89  }
90  return 0;
91 }
92 
94 {
95  GIFDemuxContext *gdc = s->priv_data;
96  AVIOContext *pb = s->pb;
97  AVStream *st;
98  int width, height, ret;
99 
100  if ((ret = resync(pb)) < 0)
101  return ret;
102 
103  gdc->delay = gdc->default_delay;
104  width = avio_rl16(pb);
105  height = avio_rl16(pb);
106 
107  if (width == 0 || height == 0)
108  return AVERROR_INVALIDDATA;
109 
110  st = avformat_new_stream(s, NULL);
111  if (!st)
112  return AVERROR(ENOMEM);
113 
114  /* GIF format operates with time in "hundredths of second",
115  * therefore timebase is 1/100 */
116  avpriv_set_pts_info(st, 64, 1, 100);
119  st->codec->width = width;
120  st->codec->height = height;
121 
122  /* jump to start because gif decoder needs header data too */
123  if (avio_seek(pb, 0, SEEK_SET) != 0)
124  return AVERROR(EIO);
125 
126  return 0;
127 }
128 
130 {
131  int sb_size, ret = 0;
132 
133  while (0x00 != (sb_size = avio_r8(pb))) {
134  if ((ret = avio_skip(pb, sb_size)) < 0)
135  return ret;
136  }
137 
138  return ret;
139 }
140 
142 {
143  GIFDemuxContext *gdc = s->priv_data;
144  AVIOContext *pb = s->pb;
145  int sb_size, ext_label = avio_r8(pb);
146  int ret;
147 
148  if (ext_label == GIF_GCE_EXT_LABEL) {
149  if ((sb_size = avio_r8(pb)) < 4) {
150  av_log(s, AV_LOG_FATAL, "Graphic Control Extension block's size less than 4.\n");
151  return AVERROR_INVALIDDATA;
152  }
153 
154  /* skip packed fields */
155  if ((ret = avio_skip(pb, 1)) < 0)
156  return ret;
157 
158  gdc->delay = avio_rl16(pb);
159 
160  if (gdc->delay < gdc->min_delay)
161  gdc->delay = gdc->default_delay;
162 
163  /* skip the rest of the Graphic Control Extension block */
164  if ((ret = avio_skip(pb, sb_size - 3)) < 0 )
165  return ret;
166  } else if (ext_label == GIF_APP_EXT_LABEL) {
167  uint8_t netscape_ext[sizeof(NETSCAPE_EXT_STR)-1 + 2];
168 
169  if ((sb_size = avio_r8(pb)) != strlen(NETSCAPE_EXT_STR))
170  return 0;
171  ret = avio_read(pb, netscape_ext, sizeof(netscape_ext));
172  if (ret < sizeof(netscape_ext))
173  return ret;
174  gdc->total_iter = avio_rl16(pb);
175  if (gdc->total_iter == 0)
176  gdc->total_iter = -1;
177  }
178 
179  if ((ret = gif_skip_subblocks(pb)) < 0)
180  return ret;
181 
182  return 0;
183 }
184 
186 {
187  GIFDemuxContext *gdc = s->priv_data;
188  AVIOContext *pb = s->pb;
189  int packed_fields, block_label, ct_size,
190  keyframe, frame_parsed = 0, ret;
191  int64_t frame_start = avio_tell(pb), frame_end;
192  unsigned char buf[6];
193 
194  if ((ret = avio_read(pb, buf, 6)) == 6) {
195  keyframe = memcmp(buf, gif87a_sig, 6) == 0 ||
196  memcmp(buf, gif89a_sig, 6) == 0;
197  } else if (ret < 0) {
198  return ret;
199  } else {
200  keyframe = 0;
201  }
202 
203  if (keyframe) {
204 parse_keyframe:
205  /* skip 2 bytes of width and 2 of height */
206  if ((ret = avio_skip(pb, 4)) < 0)
207  return ret;
208 
209  packed_fields = avio_r8(pb);
210 
211  /* skip 1 byte of Background Color Index and 1 byte of Pixel Aspect Ratio */
212  if ((ret = avio_skip(pb, 2)) < 0)
213  return ret;
214 
215  /* global color table presence */
216  if (packed_fields & 0x80) {
217  ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
218 
219  if ((ret = avio_skip(pb, ct_size)) < 0)
220  return ret;
221  }
222  } else {
223  avio_seek(pb, -ret, SEEK_CUR);
224  ret = AVERROR_EOF;
225  }
226 
227  while (GIF_TRAILER != (block_label = avio_r8(pb)) && !url_feof(pb)) {
228  if (block_label == GIF_EXTENSION_INTRODUCER) {
229  if ((ret = gif_read_ext (s)) < 0 )
230  goto resync;
231  } else if (block_label == GIF_IMAGE_SEPARATOR) {
232  /* skip to last byte of Image Descriptor header */
233  if ((ret = avio_skip(pb, 8)) < 0)
234  return ret;
235 
236  packed_fields = avio_r8(pb);
237 
238  /* local color table presence */
239  if (packed_fields & 0x80) {
240  ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
241 
242  if ((ret = avio_skip(pb, ct_size)) < 0)
243  return ret;
244  }
245 
246  /* read LZW Minimum Code Size */
247  if (avio_r8(pb) < 1) {
248  av_log(s, AV_LOG_ERROR, "lzw minimum code size must be >= 1\n");
249  goto resync;
250  }
251 
252  if ((ret = gif_skip_subblocks(pb)) < 0)
253  goto resync;
254 
255  frame_end = avio_tell(pb);
256 
257  if (avio_seek(pb, frame_start, SEEK_SET) != frame_start)
258  return AVERROR(EIO);
259 
260  ret = av_get_packet(pb, pkt, frame_end - frame_start);
261  if (ret < 0)
262  return ret;
263 
264  if (keyframe)
265  pkt->flags |= AV_PKT_FLAG_KEY;
266 
267  pkt->stream_index = 0;
268  pkt->duration = gdc->delay;
269 
270  /* Graphic Control Extension's scope is single frame.
271  * Remove its influence. */
272  gdc->delay = gdc->default_delay;
273  frame_parsed = 1;
274 
275  break;
276  } else {
277  av_log(s, AV_LOG_ERROR, "invalid block label\n");
278 resync:
279  if (!keyframe)
280  avio_seek(pb, frame_start, SEEK_SET);
281  if ((ret = resync(pb)) < 0)
282  return ret;
283  frame_start = avio_tell(pb) - 6;
284  keyframe = 1;
285  goto parse_keyframe;
286  }
287  }
288 
289  if ((ret >= 0 && !frame_parsed) || ret == AVERROR_EOF) {
290  /* This might happen when there is no image block
291  * between extension blocks and GIF_TRAILER or EOF */
292  if (!gdc->ignore_loop && (block_label == GIF_TRAILER || url_feof(pb))
293  && (gdc->total_iter < 0 || ++gdc->iter_count < gdc->total_iter))
294  return avio_seek(pb, 0, SEEK_SET);
295  return AVERROR_EOF;
296  } else
297  return ret;
298 }
299 
300 static const AVOption options[] = {
301  { "min_delay" , "minimum valid delay between frames (in hundredths of second)", offsetof(GIFDemuxContext, min_delay) , AV_OPT_TYPE_INT, {.i64 = GIF_MIN_DELAY} , 0, 100 * 60, AV_OPT_FLAG_DECODING_PARAM },
302  { "default_delay", "default delay between frames (in hundredths of second)" , offsetof(GIFDemuxContext, default_delay), AV_OPT_TYPE_INT, {.i64 = GIF_DEFAULT_DELAY}, 0, 100 * 60, AV_OPT_FLAG_DECODING_PARAM },
303  { "ignore_loop" , "ignore loop setting (netscape extension)" , offsetof(GIFDemuxContext, ignore_loop) , AV_OPT_TYPE_INT, {.i64 = 1} , 0, 1, AV_OPT_FLAG_DECODING_PARAM },
304  { NULL },
305 };
306 
307 static const AVClass demuxer_class = {
308  .class_name = "GIF demuxer",
309  .item_name = av_default_item_name,
310  .option = options,
311  .version = LIBAVUTIL_VERSION_INT,
312  .category = AV_CLASS_CATEGORY_DEMUXER,
313 };
314 
316  .name = "gif",
317  .long_name = NULL_IF_CONFIG_SMALL("CompuServe Graphics Interchange Format (GIF)"),
318  .priv_data_size = sizeof(GIFDemuxContext),
323  .priv_class = &demuxer_class,
324 };