yading@11: /*
yading@11:  * GIF demuxer
yading@11:  * Copyright (c) 2012 Vitaliy E Sugrobov
yading@11:  *
yading@11:  * This file is part of FFmpeg.
yading@11:  *
yading@11:  * FFmpeg is free software; you can redistribute it and/or
yading@11:  * modify it under the terms of the GNU Lesser General Public
yading@11:  * License as published by the Free Software Foundation; either
yading@11:  * version 2.1 of the License, or (at your option) any later version.
yading@11:  *
yading@11:  * FFmpeg is distributed in the hope that it will be useful,
yading@11:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@11:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@11:  * Lesser General Public License for more details.
yading@11:  *
yading@11:  * You should have received a copy of the GNU Lesser General Public
yading@11:  * License along with FFmpeg; if not, write to the Free Software
yading@11:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@11:  */
yading@11: 
yading@11: /**
yading@11:  * @file
yading@11:  * GIF demuxer.
yading@11:  */
yading@11: 
yading@11: #include "avformat.h"
yading@11: #include "libavutil/intreadwrite.h"
yading@11: #include "libavutil/opt.h"
yading@11: #include "internal.h"
yading@11: #include "libavcodec/gif.h"
yading@11: 
yading@11: typedef struct GIFDemuxContext {
yading@11:     const AVClass *class;
yading@11:     /**
yading@11:      * Time span in hundredths of second before
yading@11:      * the next frame should be drawn on screen.
yading@11:      */
yading@11:     int delay;
yading@11:     /**
yading@11:      * Minimum allowed delay between frames in hundredths of
yading@11:      * second. Values below this threshold considered to be
yading@11:      * invalid and set to value of default_delay.
yading@11:      */
yading@11:     int min_delay;
yading@11:     int default_delay;
yading@11: 
yading@11:     /**
yading@11:      * loop options
yading@11:      */
yading@11:     int total_iter;
yading@11:     int iter_count;
yading@11:     int ignore_loop;
yading@11: } GIFDemuxContext;
yading@11: 
yading@11: /**
yading@11:  * Major web browsers display gifs at ~10-15fps when rate
yading@11:  * is not explicitly set or have too low values. We assume default rate to be 10.
yading@11:  * Default delay = 100hundredths of second / 10fps = 10hos per frame.
yading@11:  */
yading@11: #define GIF_DEFAULT_DELAY   10
yading@11: /**
yading@11:  * By default delay values less than this threshold considered to be invalid.
yading@11:  */
yading@11: #define GIF_MIN_DELAY       2
yading@11: 
yading@11: static int gif_probe(AVProbeData *p)
yading@11: {
yading@11:     /* check magick */
yading@11:     if (memcmp(p->buf, gif87a_sig, 6) && memcmp(p->buf, gif89a_sig, 6))
yading@11:         return 0;
yading@11: 
yading@11:     /* width or height contains zero? */
yading@11:     if (!AV_RL16(&p->buf[6]) || !AV_RL16(&p->buf[8]))
yading@11:         return 0;
yading@11: 
yading@11:     return AVPROBE_SCORE_MAX;
yading@11: }
yading@11: 
yading@11: static int resync(AVIOContext *pb)
yading@11: {
yading@11:     int i;
yading@11:     for (i = 0; i < 6; i++) {
yading@11:         int b = avio_r8(pb);
yading@11:         if (b != gif87a_sig[i] && b != gif89a_sig[i])
yading@11:             i = -(b != 'G');
yading@11:         if (url_feof(pb))
yading@11:             return AVERROR_EOF;
yading@11:     }
yading@11:     return 0;
yading@11: }
yading@11: 
yading@11: static int gif_read_header(AVFormatContext *s)
yading@11: {
yading@11:     GIFDemuxContext *gdc = s->priv_data;
yading@11:     AVIOContext     *pb  = s->pb;
yading@11:     AVStream        *st;
yading@11:     int width, height, ret;
yading@11: 
yading@11:     if ((ret = resync(pb)) < 0)
yading@11:         return ret;
yading@11: 
yading@11:     gdc->delay  = gdc->default_delay;
yading@11:     width  = avio_rl16(pb);
yading@11:     height = avio_rl16(pb);
yading@11: 
yading@11:     if (width == 0 || height == 0)
yading@11:         return AVERROR_INVALIDDATA;
yading@11: 
yading@11:     st = avformat_new_stream(s, NULL);
yading@11:     if (!st)
yading@11:         return AVERROR(ENOMEM);
yading@11: 
yading@11:     /* GIF format operates with time in "hundredths of second",
yading@11:      * therefore timebase is 1/100 */
yading@11:     avpriv_set_pts_info(st, 64, 1, 100);
yading@11:     st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
yading@11:     st->codec->codec_id   = AV_CODEC_ID_GIF;
yading@11:     st->codec->width      = width;
yading@11:     st->codec->height     = height;
yading@11: 
yading@11:     /* jump to start because gif decoder needs header data too */
yading@11:     if (avio_seek(pb, 0, SEEK_SET) != 0)
yading@11:         return AVERROR(EIO);
yading@11: 
yading@11:     return 0;
yading@11: }
yading@11: 
yading@11: static int gif_skip_subblocks(AVIOContext *pb)
yading@11: {
yading@11:     int sb_size, ret = 0;
yading@11: 
yading@11:     while (0x00 != (sb_size = avio_r8(pb))) {
yading@11:         if ((ret = avio_skip(pb, sb_size)) < 0)
yading@11:             return ret;
yading@11:     }
yading@11: 
yading@11:     return ret;
yading@11: }
yading@11: 
yading@11: static int gif_read_ext(AVFormatContext *s)
yading@11: {
yading@11:     GIFDemuxContext *gdc = s->priv_data;
yading@11:     AVIOContext *pb = s->pb;
yading@11:     int sb_size, ext_label = avio_r8(pb);
yading@11:     int ret;
yading@11: 
yading@11:     if (ext_label == GIF_GCE_EXT_LABEL) {
yading@11:         if ((sb_size = avio_r8(pb)) < 4) {
yading@11:             av_log(s, AV_LOG_FATAL, "Graphic Control Extension block's size less than 4.\n");
yading@11:             return AVERROR_INVALIDDATA;
yading@11:         }
yading@11: 
yading@11:         /* skip packed fields */
yading@11:         if ((ret = avio_skip(pb, 1)) < 0)
yading@11:             return ret;
yading@11: 
yading@11:         gdc->delay = avio_rl16(pb);
yading@11: 
yading@11:         if (gdc->delay < gdc->min_delay)
yading@11:             gdc->delay = gdc->default_delay;
yading@11: 
yading@11:         /* skip the rest of the Graphic Control Extension block */
yading@11:         if ((ret = avio_skip(pb, sb_size - 3)) < 0 )
yading@11:             return ret;
yading@11:     } else if (ext_label == GIF_APP_EXT_LABEL) {
yading@11:         uint8_t netscape_ext[sizeof(NETSCAPE_EXT_STR)-1 + 2];
yading@11: 
yading@11:         if ((sb_size = avio_r8(pb)) != strlen(NETSCAPE_EXT_STR))
yading@11:             return 0;
yading@11:         ret = avio_read(pb, netscape_ext, sizeof(netscape_ext));
yading@11:         if (ret < sizeof(netscape_ext))
yading@11:             return ret;
yading@11:         gdc->total_iter = avio_rl16(pb);
yading@11:         if (gdc->total_iter == 0)
yading@11:             gdc->total_iter = -1;
yading@11:     }
yading@11: 
yading@11:     if ((ret = gif_skip_subblocks(pb)) < 0)
yading@11:         return ret;
yading@11: 
yading@11:     return 0;
yading@11: }
yading@11: 
yading@11: static int gif_read_packet(AVFormatContext *s, AVPacket *pkt)
yading@11: {
yading@11:     GIFDemuxContext *gdc = s->priv_data;
yading@11:     AVIOContext *pb = s->pb;
yading@11:     int packed_fields, block_label, ct_size,
yading@11:         keyframe, frame_parsed = 0, ret;
yading@11:     int64_t frame_start = avio_tell(pb), frame_end;
yading@11:     unsigned char buf[6];
yading@11: 
yading@11:     if ((ret = avio_read(pb, buf, 6)) == 6) {
yading@11:         keyframe = memcmp(buf, gif87a_sig, 6) == 0 ||
yading@11:                    memcmp(buf, gif89a_sig, 6) == 0;
yading@11:     } else if (ret < 0) {
yading@11:         return ret;
yading@11:     } else {
yading@11:         keyframe = 0;
yading@11:     }
yading@11: 
yading@11:     if (keyframe) {
yading@11: parse_keyframe:
yading@11:         /* skip 2 bytes of width and 2 of height */
yading@11:         if ((ret = avio_skip(pb, 4)) < 0)
yading@11:             return ret;
yading@11: 
yading@11:         packed_fields = avio_r8(pb);
yading@11: 
yading@11:         /* skip 1 byte of Background Color Index and 1 byte of Pixel Aspect Ratio */
yading@11:         if ((ret = avio_skip(pb, 2)) < 0)
yading@11:             return ret;
yading@11: 
yading@11:         /* global color table presence */
yading@11:         if (packed_fields & 0x80) {
yading@11:             ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
yading@11: 
yading@11:             if ((ret = avio_skip(pb, ct_size)) < 0)
yading@11:                 return ret;
yading@11:         }
yading@11:     } else {
yading@11:         avio_seek(pb, -ret, SEEK_CUR);
yading@11:         ret = AVERROR_EOF;
yading@11:     }
yading@11: 
yading@11:     while (GIF_TRAILER != (block_label = avio_r8(pb)) && !url_feof(pb)) {
yading@11:         if (block_label == GIF_EXTENSION_INTRODUCER) {
yading@11:             if ((ret = gif_read_ext (s)) < 0 )
yading@11:                 goto resync;
yading@11:         } else if (block_label == GIF_IMAGE_SEPARATOR) {
yading@11:             /* skip to last byte of Image Descriptor header */
yading@11:             if ((ret = avio_skip(pb, 8)) < 0)
yading@11:                 return ret;
yading@11: 
yading@11:             packed_fields = avio_r8(pb);
yading@11: 
yading@11:             /* local color table presence */
yading@11:             if (packed_fields & 0x80) {
yading@11:                 ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
yading@11: 
yading@11:                 if ((ret = avio_skip(pb, ct_size)) < 0)
yading@11:                     return ret;
yading@11:             }
yading@11: 
yading@11:             /* read LZW Minimum Code Size */
yading@11:             if (avio_r8(pb) < 1) {
yading@11:                 av_log(s, AV_LOG_ERROR, "lzw minimum code size must be >= 1\n");
yading@11:                 goto resync;
yading@11:             }
yading@11: 
yading@11:             if ((ret = gif_skip_subblocks(pb)) < 0)
yading@11:                 goto resync;
yading@11: 
yading@11:             frame_end = avio_tell(pb);
yading@11: 
yading@11:             if (avio_seek(pb, frame_start, SEEK_SET) != frame_start)
yading@11:                 return AVERROR(EIO);
yading@11: 
yading@11:             ret = av_get_packet(pb, pkt, frame_end - frame_start);
yading@11:             if (ret < 0)
yading@11:                 return ret;
yading@11: 
yading@11:             if (keyframe)
yading@11:                 pkt->flags |= AV_PKT_FLAG_KEY;
yading@11: 
yading@11:             pkt->stream_index = 0;
yading@11:             pkt->duration = gdc->delay;
yading@11: 
yading@11:             /* Graphic Control Extension's scope is single frame.
yading@11:              * Remove its influence. */
yading@11:             gdc->delay = gdc->default_delay;
yading@11:             frame_parsed = 1;
yading@11: 
yading@11:             break;
yading@11:         } else {
yading@11:             av_log(s, AV_LOG_ERROR, "invalid block label\n");
yading@11: resync:
yading@11:             if (!keyframe)
yading@11:                 avio_seek(pb, frame_start, SEEK_SET);
yading@11:             if ((ret = resync(pb)) < 0)
yading@11:                 return ret;
yading@11:             frame_start = avio_tell(pb) - 6;
yading@11:             keyframe = 1;
yading@11:             goto parse_keyframe;
yading@11:         }
yading@11:     }
yading@11: 
yading@11:     if ((ret >= 0 && !frame_parsed) || ret == AVERROR_EOF) {
yading@11:         /* This might happen when there is no image block
yading@11:          * between extension blocks and GIF_TRAILER or EOF */
yading@11:         if (!gdc->ignore_loop && (block_label == GIF_TRAILER || url_feof(pb))
yading@11:             && (gdc->total_iter < 0 || ++gdc->iter_count < gdc->total_iter))
yading@11:             return avio_seek(pb, 0, SEEK_SET);
yading@11:         return AVERROR_EOF;
yading@11:     } else
yading@11:         return ret;
yading@11: }
yading@11: 
yading@11: static const AVOption options[] = {
yading@11:     { "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 },
yading@11:     { "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 },
yading@11:     { "ignore_loop"  , "ignore loop setting (netscape extension)"                    , offsetof(GIFDemuxContext, ignore_loop)  , AV_OPT_TYPE_INT, {.i64 = 1}                , 0,        1, AV_OPT_FLAG_DECODING_PARAM },
yading@11:     { NULL },
yading@11: };
yading@11: 
yading@11: static const AVClass demuxer_class = {
yading@11:     .class_name = "GIF demuxer",
yading@11:     .item_name  = av_default_item_name,
yading@11:     .option     = options,
yading@11:     .version    = LIBAVUTIL_VERSION_INT,
yading@11:     .category   = AV_CLASS_CATEGORY_DEMUXER,
yading@11: };
yading@11: 
yading@11: AVInputFormat ff_gif_demuxer = {
yading@11:     .name           = "gif",
yading@11:     .long_name      = NULL_IF_CONFIG_SMALL("CompuServe Graphics Interchange Format (GIF)"),
yading@11:     .priv_data_size = sizeof(GIFDemuxContext),
yading@11:     .read_probe     = gif_probe,
yading@11:     .read_header    = gif_read_header,
yading@11:     .read_packet    = gif_read_packet,
yading@11:     .flags          = AVFMT_GENERIC_INDEX,
yading@11:     .priv_class     = &demuxer_class,
yading@11: };