Thilo Borgmann via ffmpeg-devel:
> From: Josef Zlomek <jo...@pex.com>
>
> Adds the demuxer of animated WebP files.
> It supports non-animated, animated, truncated, and concatenated files.
> Reading from a pipe (and other non-seekable inputs) is also supported.
This demuxer uses lots of seeks, so that the above claim is only correct
if the read buffer is large enough to allow seeking back to the start of
the data.
Apart from that: My answer to the decoder contains why I consider
splitting animations into packets a bad idea.
>
> The WebP demuxer splits the input stream into packets containing one frame.
> It also marks the key frames properly.
> The loop count is ignored by default (same behaviour as animated PNG and GIF),
> it may be enabled by the option '-ignore_loop 0'.
>
> The frame rate is set according to the frame delay in the ANMF chunk.
> If the delay is too low, or the image is not animated, the default frame rate
> is set to 10 fps, similarly to other WebP libraries and browsers.
> The fate suite was updated accordingly.
>
> Signed-off-by: Josef Zlomek <jo...@pex.com>
> ---
> Changelog | 1 +
> doc/demuxers.texi | 28 ++
> libavformat/Makefile | 1 +
> libavformat/allformats.c | 1 +
> libavformat/version.h | 2 +-
> libavformat/webpdec.c | 383 ++++++++++++++++++++
> tests/ref/fate/exif-image-webp | 8 +-
> tests/ref/fate/webp-rgb-lena-lossless | 2 +-
> tests/ref/fate/webp-rgb-lena-lossless-rgb24 | 2 +-
> tests/ref/fate/webp-rgb-lossless | 2 +-
> tests/ref/fate/webp-rgb-lossy-q80 | 2 +-
> tests/ref/fate/webp-rgba-lossless | 2 +-
> tests/ref/fate/webp-rgba-lossy-q80 | 2 +-
> 13 files changed, 425 insertions(+), 11 deletions(-)
> create mode 100644 libavformat/webpdec.c
>
> diff --git a/Changelog b/Changelog
> index 87f4dbdef4..cbf15f028a 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -63,6 +63,7 @@ version 6.1:
> variable-fields elements within the same parent element
> - ffprobe -output_format option added as an alias of -of
> - animated WebP decoder
> +- animated WebP demuxer
>
>
> version 6.0:
> diff --git a/doc/demuxers.texi b/doc/demuxers.texi
> index e4c5b560a6..fcb9f9ee3c 100644
> --- a/doc/demuxers.texi
> +++ b/doc/demuxers.texi
> @@ -943,4 +943,32 @@ which in turn, acts as a ceiling for the size of scripts
> that can be read.
> Default is 1 MiB.
> @end table
>
> +@section webp
> +
> +Animated WebP demuxer.
> +
> +It accepts the following options:
> +
> +@table @option
> +@item -min_delay @var{int}
> +Set the minimum valid delay between frames in milliseconds.
> +Range is 0 to 60000. Default value is 10.
> +
> +@item -max_webp_delay @var{int}
> +Set the maximum valid delay between frames in milliseconds.
> +Range is 0 to 16777215. Default value is 16777215 (over four hours),
> +the maximum value allowed by the specification.
> +
> +@item -default_delay @var{int}
> +Set the default delay between frames in milliseconds.
> +Range is 0 to 60000. Default value is 100.
> +
> +@item -ignore_loop @var{bool}
> +WebP files can contain information to loop a certain number of times
> +(or infinitely). If @option{ignore_loop} is set to true, then the loop
> +setting from the input will be ignored and looping will not occur.
> +If set to false, then looping will occur and will cycle the number
> +of times according to the WebP. Default value is true.
> +@end table
> +
> @c man end DEMUXERS
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index 05b9b8a115..78ed0977c6 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -622,6 +622,7 @@ OBJS-$(CONFIG_WEBM_MUXER) += matroskaenc.o
> matroska.o \
> av1.o avlanguage.o
> OBJS-$(CONFIG_WEBM_DASH_MANIFEST_MUXER) += webmdashenc.o
> OBJS-$(CONFIG_WEBM_CHUNK_MUXER) += webm_chunk.o
> +OBJS-$(CONFIG_WEBP_DEMUXER) += webpdec.o
> OBJS-$(CONFIG_WEBP_MUXER) += webpenc.o
> OBJS-$(CONFIG_WEBVTT_DEMUXER) += webvttdec.o subtitles.o
> OBJS-$(CONFIG_WEBVTT_MUXER) += webvttenc.o
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index b04b43cab3..c6a2308591 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -506,6 +506,7 @@ extern const AVInputFormat ff_webm_dash_manifest_demuxer;
> extern const FFOutputFormat ff_webm_dash_manifest_muxer;
> extern const FFOutputFormat ff_webm_chunk_muxer;
> extern const FFOutputFormat ff_webp_muxer;
> +extern const AVInputFormat ff_webp_demuxer;
> extern const AVInputFormat ff_webvtt_demuxer;
> extern const FFOutputFormat ff_webvtt_muxer;
> extern const AVInputFormat ff_wsaud_demuxer;
> diff --git a/libavformat/version.h b/libavformat/version.h
> index de9cc8e31d..f4a26c2870 100644
> --- a/libavformat/version.h
> +++ b/libavformat/version.h
> @@ -32,7 +32,7 @@
> #include "version_major.h"
>
> #define LIBAVFORMAT_VERSION_MINOR 20
> -#define LIBAVFORMAT_VERSION_MICRO 100
> +#define LIBAVFORMAT_VERSION_MICRO 101
>
> #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
> LIBAVFORMAT_VERSION_MINOR, \
> diff --git a/libavformat/webpdec.c b/libavformat/webpdec.c
> new file mode 100644
> index 0000000000..73c55ee585
> --- /dev/null
> +++ b/libavformat/webpdec.c
> @@ -0,0 +1,383 @@
> +/*
> + * WebP demuxer
> + * Copyright (c) 2020 Pexeso Inc.
> + *
> + * 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
> + * WebP demuxer.
> + */
> +
> +#include "avformat.h"
> +#include "internal.h"
> +#include "libavutil/intreadwrite.h"
> +#include "libavutil/opt.h"
> +
> +typedef struct WebPDemuxContext {
> + const AVClass *class;
> + /**
> + * Time span in milliseconds before the next frame
> + * should be drawn on screen.
> + */
> + int delay;
> + /**
> + * Minimum allowed delay between frames in milliseconds.
> + * Values below this threshold are considered to be invalid
> + * and set to value of default_delay.
> + */
> + int min_delay;
> + int max_delay;
> + int default_delay;
> +
> + /*
> + * loop options
> + */
> + int ignore_loop; ///< ignore loop setting
> + int num_loop; ///< number of times to loop the
> animation
> + int cur_loop; ///< current loop counter
> + int64_t file_start; ///< start position of the current
> animation file
> + uint32_t remaining_size; ///< remaining size of the current
> animation file
> +
> + /*
> + * variables for the key frame detection
> + */
> + int nb_frames; ///< number of frames of the current
> animation file
> + int vp8x_flags;
> + int canvas_width; ///< width of the canvas
> + int canvas_height; ///< height of the canvas
> +} WebPDemuxContext;
> +
> +/**
> + * Major web browsers display WebPs at ~10-15fps when rate is not
> + * explicitly set or have too low values. We assume default rate to be 10.
> + * Default delay = 1000 microseconds / 10fps = 100 milliseconds per frame.
> + */
> +#define WEBP_DEFAULT_DELAY 100
> +/**
> + * By default delay values less than this threshold considered to be invalid.
> + */
> +#define WEBP_MIN_DELAY 10
> +
> +static int webp_probe(const AVProbeData *p)
> +{
> + const uint8_t *b = p->buf;
> +
> + if (AV_RB32(b) == MKBETAG('R', 'I', 'F', 'F') &&
> + AV_RB32(b + 8) == MKBETAG('W', 'E', 'B', 'P'))
> + return AVPROBE_SCORE_MAX;
> +
> + return 0;
> +}
> +
> +static int webp_read_header(AVFormatContext *s)
> +{
> + WebPDemuxContext *wdc = s->priv_data;
> + AVIOContext *pb = s->pb;
> + AVStream *st;
> + int ret, n;
> + uint32_t chunk_type, chunk_size;
> + int canvas_width = 0;
> + int canvas_height = 0;
> + int width = 0;
> + int height = 0;
> +
> + wdc->delay = wdc->default_delay;
> + wdc->num_loop = 1;
> +
> + st = avformat_new_stream(s, NULL);
> + if (!st)
> + return AVERROR(ENOMEM);
> +
> + wdc->file_start = avio_tell(pb);
> + wdc->remaining_size = avio_size(pb) - wdc->file_start;
> +
> + while (wdc->remaining_size > 8 && !avio_feof(pb)) {
> + chunk_type = avio_rl32(pb);
> + chunk_size = avio_rl32(pb);
> + if (chunk_size == UINT32_MAX)
> + return AVERROR_INVALIDDATA;
> + chunk_size += chunk_size & 1;
> + if (avio_feof(pb))
> + break;
> +
> + if (wdc->remaining_size < 8 + chunk_size)
> + return AVERROR_INVALIDDATA;
> +
> + if (chunk_type == MKTAG('R', 'I', 'F', 'F')) {
> + wdc->remaining_size = 8 + chunk_size;
> + chunk_size = 4;
> + }
> +
> + wdc->remaining_size -= 8 + chunk_size;
> +
> + switch (chunk_type) {
> + case MKTAG('V', 'P', '8', 'X'):
> + if (chunk_size >= 10) {
> + avio_skip(pb, 4);
> + canvas_width = avio_rl24(pb) + 1;
> + canvas_height = avio_rl24(pb) + 1;
> + ret = avio_skip(pb, chunk_size - 10);
> + } else
> + ret = avio_skip(pb, chunk_size);
> + break;
> + case MKTAG('V', 'P', '8', ' '):
> + if (chunk_size >= 10) {
> + avio_skip(pb, 6);
> + width = avio_rl16(pb) & 0x3fff;
> + height = avio_rl16(pb) & 0x3fff;
> + ret = avio_skip(pb, chunk_size - 10);
> + } else
> + ret = avio_skip(pb, chunk_size);
> + break;
> + case MKTAG('V', 'P', '8', 'L'):
> + if (chunk_size >= 5) {
> + avio_skip(pb, 1);
> + n = avio_rl32(pb);
> + width = (n & 0x3fff) + 1; // first 14 bits
> + height = ((n >> 14) & 0x3fff) + 1; // next 14 bits
> + ret = avio_skip(pb, chunk_size - 5);
> + } else
> + ret = avio_skip(pb, chunk_size);
> + break;
> + case MKTAG('A', 'N', 'M', 'F'):
> + if (chunk_size >= 12) {
> + avio_skip(pb, 6);
> + width = avio_rl24(pb) + 1;
> + height = avio_rl24(pb) + 1;
> + ret = avio_skip(pb, chunk_size - 12);
> + } else
> + ret = avio_skip(pb, chunk_size);
> + break;
> + default:
> + ret = avio_skip(pb, chunk_size);
> + break;
> + }
> +
> + if (ret < 0)
> + return ret;
> +
> + // set canvas size if no VP8X chunk was present
> + if (!canvas_width && width > 0)
> + canvas_width = width;
> + if (!canvas_height && height > 0)
> + canvas_height = height;
> + }
> +
> + // WebP format operates with time in "milliseconds", therefore timebase
> is 1/1000
> + avpriv_set_pts_info(st, 64, 1, 1000);
> + st->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
> + st->codecpar->codec_id = AV_CODEC_ID_WEBP;
> + st->codecpar->codec_tag = MKTAG('W', 'E', 'B', 'P');
> + st->codecpar->width = canvas_width;
> + st->codecpar->height = canvas_height;
> + st->start_time = 0;
> +
> + // jump to start
> + if ((ret = avio_seek(pb, wdc->file_start, SEEK_SET)) < 0)
> + return ret;
> + wdc->remaining_size = 0;
> +
> + return 0;
> +}
> +
> +static int webp_read_packet(AVFormatContext *s, AVPacket *pkt)
> +{
> + WebPDemuxContext *wdc = s->priv_data;
> + AVIOContext *pb = s->pb;
> + int ret, n;
> + int64_t packet_start = avio_tell(pb);
> + int64_t packet_end;
> + uint32_t chunk_type;
> + uint32_t chunk_size;
> + int width = 0;
> + int height = 0;
> + int is_frame = 0;
> + int key_frame = 0;
> +
> + if (wdc->remaining_size == 0) {
> + wdc->remaining_size = avio_size(pb) - avio_tell(pb);
> + if (wdc->remaining_size == 0) { // EOF
> + int ret;
> + wdc->delay = wdc->default_delay;
> + if (wdc->ignore_loop ||
> + (wdc->num_loop && wdc->cur_loop == wdc->num_loop - 1))
> + return AVERROR_EOF;
> +
> + av_log(s, AV_LOG_DEBUG, "loop: %d\n", wdc->cur_loop);
> +
> + wdc->cur_loop++;
> + ret = avio_seek(pb, wdc->file_start, SEEK_SET);
> + if (ret < 0)
> + return AVERROR_INVALIDDATA;
> + wdc->remaining_size = avio_size(pb) - avio_tell(pb);
> + }
> + }
> +
> + while (wdc->remaining_size > 0 && !avio_feof(pb)) {
> + chunk_type = avio_rl32(pb);
> + chunk_size = avio_rl32(pb);
> + if (chunk_size == UINT32_MAX)
> + return AVERROR_INVALIDDATA;
> + chunk_size += chunk_size & 1;
> +
> + if (avio_feof(pb))
> + break;
> +
> + // dive into RIFF chunk
> + if (chunk_type == MKTAG('R', 'I', 'F', 'F') && chunk_size > 4) {
> + wdc->file_start = avio_tell(pb) - 8;
> + wdc->remaining_size = 8 + chunk_size;
> + chunk_size = 4;
> + }
> +
> + switch (chunk_type) {
> + case MKTAG('V', 'P', '8', 'X'):
> + avio_seek(pb, chunk_size, SEEK_CUR);
> + break;
> + case MKTAG('A', 'N', 'I', 'M'):
> + if (chunk_size >= 6) {
> + avio_seek(pb, 4, SEEK_CUR);
> + wdc->num_loop = avio_rb16(pb);
> + avio_seek(pb, chunk_size - 6, SEEK_CUR);
> + }
> + break;
> + case MKTAG('V', 'P', '8', ' '):
> + if (is_frame)
> + goto flush;
> + is_frame = 1;
> +
> + if (chunk_size >= 10) {
> + avio_skip(pb, 6);
> + width = avio_rl16(pb) & 0x3fff;
> + height = avio_rl16(pb) & 0x3fff;
> + wdc->nb_frames++;
> + ret = avio_skip(pb, chunk_size - 10);
> + } else
> + ret = avio_skip(pb, chunk_size);
> + break;
> + case MKTAG('V', 'P', '8', 'L'):
> + if (is_frame)
> + goto flush;
> + is_frame = 1;
> +
> + if (chunk_size >= 5) {
> + avio_skip(pb, 1);
> + n = avio_rl32(pb);
> + width = (n & 0x3fff) + 1; // first 14 bits
> + height = ((n >> 14) & 0x3fff) + 1; // next 14 bits
> + wdc->nb_frames++;
> + ret = avio_skip(pb, chunk_size - 5);
> + } else
> + ret = avio_skip(pb, chunk_size);
> + break;
> + case MKTAG('A', 'N', 'M', 'F'):
> + if (is_frame)
> + goto flush;
> +
> + if (chunk_size >= 16) {
> + avio_skip(pb, 6);
> + width = avio_rl24(pb) + 1;
> + height = avio_rl24(pb) + 1;
> + wdc->delay = avio_rl24(pb);
> + avio_skip(pb, 1); // anmf_flags
> + if (wdc->delay < wdc->min_delay)
> + wdc->delay = wdc->default_delay;
> + wdc->delay = FFMIN(wdc->delay, wdc->max_delay);
> + chunk_size = 16;
> + ret = 0;
> + } else
> + ret = avio_skip(pb, chunk_size);
> + break;
> + default:
> + ret = avio_skip(pb, chunk_size);
> + break;
> + }
> + if (ret == AVERROR_EOF) {
> + // EOF was reached but the position may still be in the middle
> + // of the buffer. Seek to the end of the buffer so that EOF is
> + // handled properly in the next invocation of webp_read_packet.
> + if ((ret = avio_seek(pb, pb->buf_end - pb->buf_ptr, SEEK_CUR) <
> 0))
> + return ret;
> + wdc->remaining_size = 0;
> + return AVERROR_EOF;
> + }
> + if (ret < 0)
> + return ret;
> +
> + if (!wdc->canvas_width && width > 0)
> + wdc->canvas_width = width;
> + if (!wdc->canvas_height && height > 0)
> + wdc->canvas_height = height;
> +
> + if (wdc->remaining_size < 8 + chunk_size)
> + return AVERROR_INVALIDDATA;
> + wdc->remaining_size -= 8 + chunk_size;
> +
> + packet_end = avio_tell(pb);
> + }
> +
> +flush:
> + if ((ret = avio_seek(pb, packet_start, SEEK_SET)) < 0)
> + return ret;
> +
> + if ((ret = av_get_packet(pb, pkt, packet_end - packet_start)) < 0)
> + return ret;
> +
> + key_frame = is_frame && wdc->nb_frames == 1;
> + if (key_frame)
> + pkt->flags |= AV_PKT_FLAG_KEY;
> + else
> + pkt->flags &= ~AV_PKT_FLAG_KEY;
> +
> + pkt->stream_index = 0;
> + pkt->duration = is_frame ? wdc->delay : 0;
> + pkt->pts = pkt->dts = AV_NOPTS_VALUE;
> +
> + if (is_frame && wdc->nb_frames == 1)
> + s->streams[0]->r_frame_rate = (AVRational) {1000, pkt->duration};
> +
> + return ret;
> +}
> +
> +static const AVOption options[] = {
> + { "min_delay" , "minimum valid delay between frames (in
> milliseconds)", offsetof(WebPDemuxContext, min_delay) , AV_OPT_TYPE_INT,
> {.i64 = WEBP_MIN_DELAY} , 0, 1000 * 60, AV_OPT_FLAG_DECODING_PARAM },
> + { "max_webp_delay", "maximum valid delay between frames (in
> milliseconds)", offsetof(WebPDemuxContext, max_delay) , AV_OPT_TYPE_INT,
> {.i64 = 0xffffff} , 0, 0xffffff , AV_OPT_FLAG_DECODING_PARAM },
> + { "default_delay" , "default delay between frames (in milliseconds)"
> , offsetof(WebPDemuxContext, default_delay), AV_OPT_TYPE_INT, {.i64 =
> WEBP_DEFAULT_DELAY}, 0, 1000 * 60, AV_OPT_FLAG_DECODING_PARAM },
> + { "ignore_loop" , "ignore loop setting"
> , offsetof(WebPDemuxContext, ignore_loop) , AV_OPT_TYPE_BOOL,{.i64 = 1}
> , 0, 1 , AV_OPT_FLAG_DECODING_PARAM },
> + { NULL },
> +};
> +
> +static const AVClass demuxer_class = {
> + .class_name = "WebP demuxer",
> + .item_name = av_default_item_name,
> + .option = options,
> + .version = LIBAVUTIL_VERSION_INT,
> + .category = AV_CLASS_CATEGORY_DEMUXER,
> +};
> +
> +AVInputFormat ff_webp_demuxer = {
Missing const
> + .name = "webp",
> + .long_name = NULL_IF_CONFIG_SMALL("WebP image"),
> + .priv_data_size = sizeof(WebPDemuxContext),
> + .read_probe = webp_probe,
> + .read_header = webp_read_header,
> + .read_packet = webp_read_packet,
> + .flags = AVFMT_GENERIC_INDEX,
> + .priv_class = &demuxer_class,
> +};
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