/* * 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; } 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 gif_read_header(AVFormatContext *s) { GIFDemuxContext *gdc = s->priv_data; AVIOContext *pb = s->pb; AVStream *st; int width, height, ret; /* skip 6-byte magick */ if ((ret = avio_skip(pb, 6)) < 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; } 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) { /* 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; /* glogal 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 ) return ret; } 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"); return AVERROR_INVALIDDATA; } if ((ret = gif_skip_subblocks(pb)) < 0) return ret; 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"); return AVERROR_INVALIDDATA; } } if (ret >= 0 && !frame_parsed) { /* This might happen when there is no image block * between extension blocks and GIF_TRAILER or EOF */ 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 }, { 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, };