/*
* GIF demuxer
* Copyright (c) 2012 Vitaliy E Sugrobov
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* GIF demuxer.
*/
#include "avformat.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/opt.h"
#include "internal.h"
#include "libavcodec/gif.h"
typedef struct GIFDemuxContext {
const AVClass *class;
/**
* Time span in hundredths of second before
* the next frame should be drawn on screen.
*/
int delay;
/**
* Minimum allowed delay between frames in hundredths of
* second. Values below this threshold considered to be
* invalid and set to value of default_delay.
*/
int min_delay;
int default_delay;
/**
* loop options
*/
int total_iter;
int iter_count;
int ignore_loop;
} GIFDemuxContext;
/**
* Major web browsers display gifs at ~10-15fps when rate
* is not explicitly set or have too low values. We assume default rate to be 10.
* Default delay = 100hundredths of second / 10fps = 10hos per frame.
*/
#define GIF_DEFAULT_DELAY 10
/**
* By default delay values less than this threshold considered to be invalid.
*/
#define GIF_MIN_DELAY 2
static int gif_probe(AVProbeData *p)
{
/* check magick */
if (memcmp(p->buf, gif87a_sig, 6) && memcmp(p->buf, gif89a_sig, 6))
return 0;
/* width or height contains zero? */
if (!AV_RL16(&p->buf[6]) || !AV_RL16(&p->buf[8]))
return 0;
return AVPROBE_SCORE_MAX;
}
static int resync(AVIOContext *pb)
{
int i;
for (i = 0; i < 6; i++) {
int b = avio_r8(pb);
if (b != gif87a_sig[i] && b != gif89a_sig[i])
i = -(b != 'G');
if (url_feof(pb))
return AVERROR_EOF;
}
return 0;
}
static int gif_read_header(AVFormatContext *s)
{
GIFDemuxContext *gdc = s->priv_data;
AVIOContext *pb = s->pb;
AVStream *st;
int width, height, ret;
if ((ret = resync(pb)) < 0)
return ret;
gdc->delay = gdc->default_delay;
width = avio_rl16(pb);
height = avio_rl16(pb);
if (width == 0 || height == 0)
return AVERROR_INVALIDDATA;
st = avformat_new_stream(s, NULL);
if (!st)
return AVERROR(ENOMEM);
/* GIF format operates with time in "hundredths of second",
* therefore timebase is 1/100 */
avpriv_set_pts_info(st, 64, 1, 100);
st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
st->codec->codec_id = AV_CODEC_ID_GIF;
st->codec->width = width;
st->codec->height = height;
/* jump to start because gif decoder needs header data too */
if (avio_seek(pb, 0, SEEK_SET) != 0)
return AVERROR(EIO);
return 0;
}
static int gif_skip_subblocks(AVIOContext *pb)
{
int sb_size, ret = 0;
while (0x00 != (sb_size = avio_r8(pb))) {
if ((ret = avio_skip(pb, sb_size)) < 0)
return ret;
}
return ret;
}
static int gif_read_ext(AVFormatContext *s)
{
GIFDemuxContext *gdc = s->priv_data;
AVIOContext *pb = s->pb;
int sb_size, ext_label = avio_r8(pb);
int ret;
if (ext_label == GIF_GCE_EXT_LABEL) {
if ((sb_size = avio_r8(pb)) < 4) {
av_log(s, AV_LOG_FATAL, "Graphic Control Extension block's size less than 4.\n");
return AVERROR_INVALIDDATA;
}
/* skip packed fields */
if ((ret = avio_skip(pb, 1)) < 0)
return ret;
gdc->delay = avio_rl16(pb);
if (gdc->delay < gdc->min_delay)
gdc->delay = gdc->default_delay;
/* skip the rest of the Graphic Control Extension block */
if ((ret = avio_skip(pb, sb_size - 3)) < 0 )
return ret;
} else if (ext_label == GIF_APP_EXT_LABEL) {
uint8_t data[256];
sb_size = avio_r8(pb);
ret = avio_read(pb, data, sb_size);
if (ret < 0 || !sb_size)
return ret;
if (sb_size == strlen(NETSCAPE_EXT_STR)) {
sb_size = avio_r8(pb);
ret = avio_read(pb, data, sb_size);
if (ret < 0 || !sb_size)
return ret;
if (sb_size == 3 && data[0] == 1) {
gdc->total_iter = AV_RL16(data+1);
if (gdc->total_iter == 0)
gdc->total_iter = -1;
}
}
}
if ((ret = gif_skip_subblocks(pb)) < 0)
return ret;
return 0;
}
static int gif_read_packet(AVFormatContext *s, AVPacket *pkt)
{
GIFDemuxContext *gdc = s->priv_data;
AVIOContext *pb = s->pb;
int packed_fields, block_label, ct_size,
keyframe, frame_parsed = 0, ret;
int64_t frame_start = avio_tell(pb), frame_end;
unsigned char buf[6];
if ((ret = avio_read(pb, buf, 6)) == 6) {
keyframe = memcmp(buf, gif87a_sig, 6) == 0 ||
memcmp(buf, gif89a_sig, 6) == 0;
} else if (ret < 0) {
return ret;
} else {
keyframe = 0;
}
if (keyframe) {
parse_keyframe:
/* skip 2 bytes of width and 2 of height */
if ((ret = avio_skip(pb, 4)) < 0)
return ret;
packed_fields = avio_r8(pb);
/* skip 1 byte of Background Color Index and 1 byte of Pixel Aspect Ratio */
if ((ret = avio_skip(pb, 2)) < 0)
return ret;
/* global color table presence */
if (packed_fields & 0x80) {
ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
if ((ret = avio_skip(pb, ct_size)) < 0)
return ret;
}
} else {
avio_seek(pb, -ret, SEEK_CUR);
ret = AVERROR_EOF;
}
while (GIF_TRAILER != (block_label = avio_r8(pb)) && !url_feof(pb)) {
if (block_label == GIF_EXTENSION_INTRODUCER) {
if ((ret = gif_read_ext (s)) < 0 )
goto resync;
} else if (block_label == GIF_IMAGE_SEPARATOR) {
/* skip to last byte of Image Descriptor header */
if ((ret = avio_skip(pb, 8)) < 0)
return ret;
packed_fields = avio_r8(pb);
/* local color table presence */
if (packed_fields & 0x80) {
ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
if ((ret = avio_skip(pb, ct_size)) < 0)
return ret;
}
/* read LZW Minimum Code Size */
if (avio_r8(pb) < 1) {
av_log(s, AV_LOG_ERROR, "lzw minimum code size must be >= 1\n");
goto resync;
}
if ((ret = gif_skip_subblocks(pb)) < 0)
goto resync;
frame_end = avio_tell(pb);
if (avio_seek(pb, frame_start, SEEK_SET) != frame_start)
return AVERROR(EIO);
ret = av_get_packet(pb, pkt, frame_end - frame_start);
if (ret < 0)
return ret;
if (keyframe)
pkt->flags |= AV_PKT_FLAG_KEY;
pkt->stream_index = 0;
pkt->duration = gdc->delay;
/* Graphic Control Extension's scope is single frame.
* Remove its influence. */
gdc->delay = gdc->default_delay;
frame_parsed = 1;
break;
} else {
av_log(s, AV_LOG_ERROR, "invalid block label\n");
resync:
if (!keyframe)
avio_seek(pb, frame_start, SEEK_SET);
if ((ret = resync(pb)) < 0)
return ret;
frame_start = avio_tell(pb) - 6;
keyframe = 1;
goto parse_keyframe;
}
}
if ((ret >= 0 && !frame_parsed) || ret == AVERROR_EOF) {
/* This might happen when there is no image block
* between extension blocks and GIF_TRAILER or EOF */
if (!gdc->ignore_loop && (block_label == GIF_TRAILER || url_feof(pb))
&& (gdc->total_iter < 0 || ++gdc->iter_count < gdc->total_iter))
return avio_seek(pb, 0, SEEK_SET);
return AVERROR_EOF;
} else
return ret;
}
static const AVOption options[] = {
{ "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 },
{ "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 },
{ "ignore_loop" , "ignore loop setting (netscape extension)" , offsetof(GIFDemuxContext, ignore_loop) , AV_OPT_TYPE_INT, {.i64 = 1} , 0, 1, AV_OPT_FLAG_DECODING_PARAM },
{ NULL },
};
static const AVClass demuxer_class = {
.class_name = "GIF demuxer",
.item_name = av_default_item_name,
.option = options,
.version = LIBAVUTIL_VERSION_INT,
.category = AV_CLASS_CATEGORY_DEMUXER,
};
AVInputFormat ff_gif_demuxer = {
.name = "gif",
.long_name = NULL_IF_CONFIG_SMALL("CompuServe Graphics Interchange Format (GIF)"),
.priv_data_size = sizeof(GIFDemuxContext),
.read_probe = gif_probe,
.read_header = gif_read_header,
.read_packet = gif_read_packet,
.flags = AVFMT_GENERIC_INDEX,
.priv_class = &demuxer_class,
};