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.
50 * Major web browsers display gifs at ~10-15fps when rate
51 * is not explicitly set or have too low values. We assume default rate to be 10.
52 * Default delay = 100hundredths of second / 10fps = 10hos per frame.
54 #define GIF_DEFAULT_DELAY 10
56 * By default delay values less than this threshold considered to be invalid.
58 #define GIF_MIN_DELAY 2
60 static int gif_probe(AVProbeData *p)
63 if (memcmp(p->buf, gif87a_sig, 6) && memcmp(p->buf, gif89a_sig, 6))
66 /* width or height contains zero? */
67 if (!AV_RL16(&p->buf[6]) || !AV_RL16(&p->buf[8]))
70 return AVPROBE_SCORE_MAX;
73 static int resync(AVIOContext *pb)
76 for (i = 0; i < 6; i++) {
78 if (b != gif87a_sig[i] && b != gif89a_sig[i])
86 static int gif_read_header(AVFormatContext *s)
88 GIFDemuxContext *gdc = s->priv_data;
89 AVIOContext *pb = s->pb;
91 int width, height, ret;
93 if ((ret = resync(pb)) < 0)
96 gdc->delay = gdc->default_delay;
97 width = avio_rl16(pb);
98 height = avio_rl16(pb);
100 if (width == 0 || height == 0)
101 return AVERROR_INVALIDDATA;
103 st = avformat_new_stream(s, NULL);
105 return AVERROR(ENOMEM);
107 /* GIF format operates with time in "hundredths of second",
108 * therefore timebase is 1/100 */
109 avpriv_set_pts_info(st, 64, 1, 100);
110 st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
111 st->codec->codec_id = AV_CODEC_ID_GIF;
112 st->codec->width = width;
113 st->codec->height = height;
115 /* jump to start because gif decoder needs header data too */
116 if (avio_seek(pb, 0, SEEK_SET) != 0)
122 static int gif_skip_subblocks(AVIOContext *pb)
124 int sb_size, ret = 0;
126 while (0x00 != (sb_size = avio_r8(pb))) {
127 if ((ret = avio_skip(pb, sb_size)) < 0)
134 static int gif_read_ext(AVFormatContext *s)
136 GIFDemuxContext *gdc = s->priv_data;
137 AVIOContext *pb = s->pb;
138 int sb_size, ext_label = avio_r8(pb);
141 if (ext_label == GIF_GCE_EXT_LABEL) {
142 if ((sb_size = avio_r8(pb)) < 4) {
143 av_log(s, AV_LOG_FATAL, "Graphic Control Extension block's size less than 4.\n");
144 return AVERROR_INVALIDDATA;
147 /* skip packed fields */
148 if ((ret = avio_skip(pb, 1)) < 0)
151 gdc->delay = avio_rl16(pb);
153 if (gdc->delay < gdc->min_delay)
154 gdc->delay = gdc->default_delay;
156 /* skip the rest of the Graphic Control Extension block */
157 if ((ret = avio_skip(pb, sb_size - 3)) < 0 )
161 if ((ret = gif_skip_subblocks(pb)) < 0)
167 static int gif_read_packet(AVFormatContext *s, AVPacket *pkt)
169 GIFDemuxContext *gdc = s->priv_data;
170 AVIOContext *pb = s->pb;
171 int packed_fields, block_label, ct_size,
172 keyframe, frame_parsed = 0, ret;
173 int64_t frame_start = avio_tell(pb), frame_end;
174 unsigned char buf[6];
176 if ((ret = avio_read(pb, buf, 6)) == 6) {
177 keyframe = memcmp(buf, gif87a_sig, 6) == 0 ||
178 memcmp(buf, gif89a_sig, 6) == 0;
179 } else if (ret < 0) {
187 /* skip 2 bytes of width and 2 of height */
188 if ((ret = avio_skip(pb, 4)) < 0)
191 packed_fields = avio_r8(pb);
193 /* skip 1 byte of Background Color Index and 1 byte of Pixel Aspect Ratio */
194 if ((ret = avio_skip(pb, 2)) < 0)
197 /* global color table presence */
198 if (packed_fields & 0x80) {
199 ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
201 if ((ret = avio_skip(pb, ct_size)) < 0)
205 avio_seek(pb, -ret, SEEK_CUR);
209 while (GIF_TRAILER != (block_label = avio_r8(pb)) && !url_feof(pb)) {
210 if (block_label == GIF_EXTENSION_INTRODUCER) {
211 if ((ret = gif_read_ext (s)) < 0 )
213 } else if (block_label == GIF_IMAGE_SEPARATOR) {
214 /* skip to last byte of Image Descriptor header */
215 if ((ret = avio_skip(pb, 8)) < 0)
218 packed_fields = avio_r8(pb);
220 /* local color table presence */
221 if (packed_fields & 0x80) {
222 ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
224 if ((ret = avio_skip(pb, ct_size)) < 0)
228 /* read LZW Minimum Code Size */
229 if (avio_r8(pb) < 1) {
230 av_log(s, AV_LOG_ERROR, "lzw minimum code size must be >= 1\n");
234 if ((ret = gif_skip_subblocks(pb)) < 0)
237 frame_end = avio_tell(pb);
239 if (avio_seek(pb, frame_start, SEEK_SET) != frame_start)
242 ret = av_get_packet(pb, pkt, frame_end - frame_start);
247 pkt->flags |= AV_PKT_FLAG_KEY;
249 pkt->stream_index = 0;
250 pkt->duration = gdc->delay;
252 /* Graphic Control Extension's scope is single frame.
253 * Remove its influence. */
254 gdc->delay = gdc->default_delay;
259 av_log(s, AV_LOG_ERROR, "invalid block label\n");
262 avio_seek(pb, frame_start, SEEK_SET);
263 if ((ret = resync(pb)) < 0)
265 frame_start = avio_tell(pb) - 6;
271 if (ret >= 0 && !frame_parsed) {
272 /* This might happen when there is no image block
273 * between extension blocks and GIF_TRAILER or EOF */
279 static const AVOption options[] = {
280 { "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 },
281 { "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 },
285 static const AVClass demuxer_class = {
286 .class_name = "GIF demuxer",
287 .item_name = av_default_item_name,
289 .version = LIBAVUTIL_VERSION_INT,
290 .category = AV_CLASS_CATEGORY_DEMUXER,
293 AVInputFormat ff_gif_demuxer = {
295 .long_name = NULL_IF_CONFIG_SMALL("CompuServe Graphics Interchange Format (GIF)"),
296 .priv_data_size = sizeof(GIFDemuxContext),
297 .read_probe = gif_probe,
298 .read_header = gif_read_header,
299 .read_packet = gif_read_packet,
300 .flags = AVFMT_GENERIC_INDEX,
301 .priv_class = &demuxer_class,