Quoting Vittorio Giovara (2016-03-21 20:09:41)
> From: Vitaliy E Sugrobov <[email protected]>
>
> This demuxer is capable of extracting multiple frames from GIF file.
> In conjunction with GIF decoder it implements support for reading
> animated GIFs.
>
> Signed-off-by: Vitaliy E Sugrobov <[email protected]>
> Signed-off-by: Vittorio Giovara <[email protected]>
> ---
> Changelog | 1 +
> doc/general.texi | 2 +-
> libavformat/Makefile | 1 +
> libavformat/allformats.c | 2 +-
> libavformat/gifdec.c | 322
> +++++++++++++++++++++++++++++++++++++++++++++++
> libavformat/version.h | 2 +-
> 6 files changed, 327 insertions(+), 3 deletions(-)
> create mode 100644 libavformat/gifdec.c
>
> diff --git a/Changelog b/Changelog
> index ca9c9b4..71fe9e2 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -52,6 +52,7 @@ version <next>:
> - G.723.1 muxer and encoder
> - compressed SWF
> - G.729 raw demuxer
> +- GIF demuxer
>
>
> version 11:
> diff --git a/doc/general.texi b/doc/general.texi
> index 40d3f4a..0f89278 100644
> --- a/doc/general.texi
> +++ b/doc/general.texi
> @@ -282,7 +282,7 @@ library:
> @item framecrc testing format @tab X @tab
> @item FunCom ISS @tab @tab X
> @tab Audio format used in various games from FunCom like The Longest
> Journey.
> -@item GIF Animation @tab X @tab
> +@item GIF Animation @tab X @tab X
> @item GXF @tab X @tab X
> @tab General eXchange Format SMPTE 360M, used by Thomson Grass Valley
> playout servers.
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index 0095e30..3814e14 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -134,6 +134,7 @@ OBJS-$(CONFIG_FLV_MUXER) += flvenc.o avc.o
> OBJS-$(CONFIG_FOURXM_DEMUXER) += 4xm.o
> OBJS-$(CONFIG_FRAMECRC_MUXER) += framecrcenc.o framehash.o
> OBJS-$(CONFIG_FRAMEMD5_MUXER) += md5enc.o framehash.o
> +OBJS-$(CONFIG_GIF_DEMUXER) += gifdec.o
> OBJS-$(CONFIG_GIF_MUXER) += gifenc.o
> OBJS-$(CONFIG_GSM_DEMUXER) += gsmdec.o
> OBJS-$(CONFIG_GXF_DEMUXER) += gxf.o
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index 0f49756..1056d7b 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -106,7 +106,7 @@ void av_register_all(void)
> REGISTER_MUXDEMUX(G722, g722);
> REGISTER_MUXDEMUX(G723_1, g723_1);
> REGISTER_DEMUXER (G729, g729);
> - REGISTER_MUXER (GIF, gif);
> + REGISTER_MUXDEMUX(GIF, gif);
> REGISTER_DEMUXER (GSM, gsm);
> REGISTER_MUXDEMUX(GXF, gxf);
> REGISTER_MUXDEMUX(H261, h261);
> diff --git a/libavformat/gifdec.c b/libavformat/gifdec.c
> new file mode 100644
> index 0000000..db210b9
> --- /dev/null
> +++ b/libavformat/gifdec.c
> @@ -0,0 +1,322 @@
> +/*
> + * GIF demuxer
> + * Copyright (c) 2012 Vitaliy E Sugrobov
> + *
> + * This file is part of Libav.
> + *
> + * Libav 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.
> + *
> + * Libav 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 Libav; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
> USA
> + */
> +
> +/**
> + * @file
> + * GIF demuxer
> + *
> + * There are two options available to users: default_delay and min_delay.
> + *
> + * These options are for protection from too rapid GIF animations. In
> practice
> + * the standard approach is to slow down rendering of this kind of GIF. If
> you
> + * try to play a GIF with a delay between frames of one hundredth of a second
> + * (100fps) using one of the major web browsers, you get significantly slower
> + * playback, around 10 fps. This is because the browser detects that the
> delay
> + * value is less than some threshold (usually 2 hundredths of a second) and
> + * resets it to the default value (usually 10 hundredths of a second, which
> + * corresponds to 10fps). By manipulating these options, users can achieve
> + * the same effect during conversion to some video format, or to not protect
> + * against rapid animations at all.
> + *
> + * The other case when these options are necessary is for GIF images encoded
> + * according to the GIF87a standard since prior to GIF89a there was no delay
> + * information included in GIF files.
> + */
A better place for this is probably doc/demuxers.texi
> +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;
> + int keyframe, frame_parsed = 0;
> + int ret;
> + int64_t frame_start = avio_tell(pb), frame_end;
> + unsigned char buf[6];
> +
> + if ((ret = avio_read(pb, buf, 6)) < 0)
> + return ret;
> +
> + keyframe = memcmp(buf, GIF_SIG_87A, 6) == 0 ||
> + memcmp(buf, GIF_SIG_89A, 6) == 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 */
^
tyop
> + if (packed_fields & 0x80) {
> + ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
> +
> + if ((ret = avio_skip(pb, ct_size)) < 0)
> + return ret;
> + }
> +
> + gdc->total_duration = 0;
> + } else {
> + avio_seek(pb, -ret, SEEK_CUR);
> + ret = AVERROR_EOF;
> + }
> +
> + while (GIF_TRAILER != (block_label = avio_r8(pb)) && !pb->eof_reached) {
This condition is concentrated evil. Just add another case with goto end
to the switch.
--
Anton Khirnov
_______________________________________________
libav-devel mailing list
[email protected]
https://lists.libav.org/mailman/listinfo/libav-devel
