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