3 * Copyright (c) 2012 Vitaliy E Sugrobov
5 * This file is part of FFmpeg.
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.
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.
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
28 #include "libavutil/intreadwrite.h"
29 #include "libavutil/opt.h"
31 #include "libavcodec/gif.h"
33 typedef struct GIFDemuxContext
{
36 * Time span in hundredths of second before
37 * the next frame should be drawn on screen.
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.
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.
61 #define GIF_DEFAULT_DELAY 10
63 * By default delay values less than this threshold considered to be invalid.
65 #define GIF_MIN_DELAY 2
67 static int gif_probe(AVProbeData
*p
)
70 if (memcmp(p
->buf
, gif87a_sig
, 6) && memcmp(p
->buf
, gif89a_sig
, 6))
73 /* width or height contains zero? */
74 if (!AV_RL16(&p
->buf
[6]) || !AV_RL16(&p
->buf
[8]))
77 return AVPROBE_SCORE_MAX
;
80 static int resync(AVIOContext
*pb
)
83 for (i
= 0; i
< 6; i
++) {
85 if (b
!= gif87a_sig
[i
] && b
!= gif89a_sig
[i
])
93 static int gif_read_header(AVFormatContext
*s
)
95 GIFDemuxContext
*gdc
= s
->priv_data
;
96 AVIOContext
*pb
= s
->pb
;
98 int width
, height
, ret
;
100 if ((ret
= resync(pb
)) < 0)
103 gdc
->delay
= gdc
->default_delay
;
104 width
= avio_rl16(pb
);
105 height
= avio_rl16(pb
);
107 if (width
== 0 || height
== 0)
108 return AVERROR_INVALIDDATA
;
110 st
= avformat_new_stream(s
, NULL
);
112 return AVERROR(ENOMEM
);
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);
117 st
->codec
->codec_type
= AVMEDIA_TYPE_VIDEO
;
118 st
->codec
->codec_id
= AV_CODEC_ID_GIF
;
119 st
->codec
->width
= width
;
120 st
->codec
->height
= height
;
122 /* jump to start because gif decoder needs header data too */
123 if (avio_seek(pb
, 0, SEEK_SET
) != 0)
129 static int gif_skip_subblocks(AVIOContext
*pb
)
131 int sb_size
, ret
= 0;
133 while (0x00 != (sb_size
= avio_r8(pb
))) {
134 if ((ret
= avio_skip(pb
, sb_size
)) < 0)
141 static int gif_read_ext(AVFormatContext
*s
)
143 GIFDemuxContext
*gdc
= s
->priv_data
;
144 AVIOContext
*pb
= s
->pb
;
145 int sb_size
, ext_label
= avio_r8(pb
);
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
;
154 /* skip packed fields */
155 if ((ret
= avio_skip(pb
, 1)) < 0)
158 gdc
->delay
= avio_rl16(pb
);
160 if (gdc
->delay
< gdc
->min_delay
)
161 gdc
->delay
= gdc
->default_delay
;
163 /* skip the rest of the Graphic Control Extension block */
164 if ((ret
= avio_skip(pb
, sb_size
- 3)) < 0 )
166 } else if (ext_label
== GIF_APP_EXT_LABEL
) {
169 sb_size
= avio_r8(pb
);
170 ret
= avio_read(pb
, data
, sb_size
);
171 if (ret
< 0 || !sb_size
)
174 if (sb_size
== strlen(NETSCAPE_EXT_STR
)) {
175 sb_size
= avio_r8(pb
);
176 ret
= avio_read(pb
, data
, sb_size
);
177 if (ret
< 0 || !sb_size
)
180 if (sb_size
== 3 && data
[0] == 1) {
181 gdc
->total_iter
= AV_RL16(data
+1);
183 if (gdc
->total_iter
== 0)
184 gdc
->total_iter
= -1;
189 if ((ret
= gif_skip_subblocks(pb
)) < 0)
195 static int gif_read_packet(AVFormatContext
*s
, AVPacket
*pkt
)
197 GIFDemuxContext
*gdc
= s
->priv_data
;
198 AVIOContext
*pb
= s
->pb
;
199 int packed_fields
, block_label
, ct_size
,
200 keyframe
, frame_parsed
= 0, ret
;
201 int64_t frame_start
= avio_tell(pb
), frame_end
;
202 unsigned char buf
[6];
204 if ((ret
= avio_read(pb
, buf
, 6)) == 6) {
205 keyframe
= memcmp(buf
, gif87a_sig
, 6) == 0 ||
206 memcmp(buf
, gif89a_sig
, 6) == 0;
207 } else if (ret
< 0) {
215 /* skip 2 bytes of width and 2 of height */
216 if ((ret
= avio_skip(pb
, 4)) < 0)
219 packed_fields
= avio_r8(pb
);
221 /* skip 1 byte of Background Color Index and 1 byte of Pixel Aspect Ratio */
222 if ((ret
= avio_skip(pb
, 2)) < 0)
225 /* global color table presence */
226 if (packed_fields
& 0x80) {
227 ct_size
= 3 * (1 << ((packed_fields
& 0x07) + 1));
229 if ((ret
= avio_skip(pb
, ct_size
)) < 0)
233 avio_seek(pb
, -ret
, SEEK_CUR
);
237 while (GIF_TRAILER
!= (block_label
= avio_r8(pb
)) && !avio_feof(pb
)) {
238 if (block_label
== GIF_EXTENSION_INTRODUCER
) {
239 if ((ret
= gif_read_ext (s
)) < 0 )
241 } else if (block_label
== GIF_IMAGE_SEPARATOR
) {
242 /* skip to last byte of Image Descriptor header */
243 if ((ret
= avio_skip(pb
, 8)) < 0)
246 packed_fields
= avio_r8(pb
);
248 /* local color table presence */
249 if (packed_fields
& 0x80) {
250 ct_size
= 3 * (1 << ((packed_fields
& 0x07) + 1));
252 if ((ret
= avio_skip(pb
, ct_size
)) < 0)
256 /* read LZW Minimum Code Size */
257 if (avio_r8(pb
) < 1) {
258 av_log(s
, AV_LOG_ERROR
, "lzw minimum code size must be >= 1\n");
262 if ((ret
= gif_skip_subblocks(pb
)) < 0)
265 frame_end
= avio_tell(pb
);
267 if (avio_seek(pb
, frame_start
, SEEK_SET
) != frame_start
)
270 ret
= av_get_packet(pb
, pkt
, frame_end
- frame_start
);
275 pkt
->flags
|= AV_PKT_FLAG_KEY
;
277 pkt
->stream_index
= 0;
278 pkt
->duration
= gdc
->delay
;
280 /* Graphic Control Extension's scope is single frame.
281 * Remove its influence. */
282 gdc
->delay
= gdc
->default_delay
;
287 av_log(s
, AV_LOG_ERROR
, "invalid block label\n");
290 avio_seek(pb
, frame_start
, SEEK_SET
);
291 if ((ret
= resync(pb
)) < 0)
293 frame_start
= avio_tell(pb
) - 6;
299 if ((ret
>= 0 && !frame_parsed
) || ret
== AVERROR_EOF
) {
300 /* This might happen when there is no image block
301 * between extension blocks and GIF_TRAILER or EOF */
302 if (!gdc
->ignore_loop
&& (block_label
== GIF_TRAILER
|| avio_feof(pb
))
303 && (gdc
->total_iter
< 0 || ++gdc
->iter_count
< gdc
->total_iter
))
304 return avio_seek(pb
, 0, SEEK_SET
);
310 static const AVOption options
[] = {
311 { "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
},
312 { "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
},
313 { "ignore_loop" , "ignore loop setting (netscape extension)" , offsetof(GIFDemuxContext
, ignore_loop
) , AV_OPT_TYPE_INT
, {.i64
= 1} , 0, 1, AV_OPT_FLAG_DECODING_PARAM
},
317 static const AVClass demuxer_class
= {
318 .class_name
= "GIF demuxer",
319 .item_name
= av_default_item_name
,
321 .version
= LIBAVUTIL_VERSION_INT
,
322 .category
= AV_CLASS_CATEGORY_DEMUXER
,
325 AVInputFormat ff_gif_demuxer
= {
327 .long_name
= NULL_IF_CONFIG_SMALL("CompuServe Graphics Interchange Format (GIF)"),
328 .priv_data_size
= sizeof(GIFDemuxContext
),
329 .read_probe
= gif_probe
,
330 .read_header
= gif_read_header
,
331 .read_packet
= gif_read_packet
,
332 .flags
= AVFMT_GENERIC_INDEX
,
333 .priv_class
= &demuxer_class
,