[FFmpeg-devel] [PATCH] Write WebVTT output files
Clément Bœsch
ubitux at gmail.com
Wed Jun 12 09:11:15 CEST 2013
On Tue, Jun 11, 2013 at 04:24:27PM -0700, Matthew Heaney wrote:
> This revision creates a WebVTT muxer, that outputs files having the
> format described in the following specification:
>
> http://dev.w3.org/html5/webvtt/
> ---
> libavformat/Makefile | 1 +
> libavformat/allformats.c | 1 +
> libavformat/webvttenc.c | 139 +++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 141 insertions(+)
> create mode 100644 libavformat/webvttenc.c
>
Missing update of doc/general.texi and minor bump in lavf/version.h
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index 5438b48..3cb076b 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -393,6 +393,7 @@ OBJS-$(CONFIG_WEBM_MUXER) += matroskaenc.o matroska.o \
> isom.o avc.o \
> flacenc_header.o avlanguage.o wv.o
> OBJS-$(CONFIG_WEBVTT_DEMUXER) += webvttdec.o subtitles.o
> +OBJS-$(CONFIG_WEBVTT_MUXER) += webvttenc.o subtitles.o
> OBJS-$(CONFIG_WSAUD_DEMUXER) += westwood_aud.o
> OBJS-$(CONFIG_WSVQA_DEMUXER) += westwood_vqa.o
> OBJS-$(CONFIG_WTV_DEMUXER) += wtvdec.o wtv.o asfdec.o asf.o asfcrypt.o \
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index 6274a75..f947e19 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -293,6 +293,7 @@ void av_register_all(void)
> REGISTER_DEMUXER (WC3, wc3);
> REGISTER_MUXER (WEBM, webm);
> REGISTER_DEMUXER (WEBVTT, webvtt);
> + REGISTER_MUXER (WEBVTT, webvtt);
REGISTER_MUXDEMUX(WEBVTT, webvtt);
> REGISTER_DEMUXER (WSAUD, wsaud);
> REGISTER_DEMUXER (WSVQA, wsvqa);
> REGISTER_MUXDEMUX(WTV, wtv);
> diff --git a/libavformat/webvttenc.c b/libavformat/webvttenc.c
> new file mode 100644
> index 0000000..45cdec9
> --- /dev/null
> +++ b/libavformat/webvttenc.c
> @@ -0,0 +1,139 @@
> +/*
> + * Copyright (c) 2013 Matthew Heaney
> + *
> + * 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
> + * WebVTT subtitle muxer
> + * @see http://dev.w3.org/html5/webvtt/
> + */
> +
> +#include "avformat.h"
> +
> +typedef struct WebVTTMuxContext {
> + const AVClass *class;
> +} WebVTTMuxContext;
> +
If you don't plan to store anything in the context, you can drop this.
> +static void webvtt_write_time(AVIOContext *pb,
> + int64_t pts,
> + const AVRational* time_base)
> +{
> + int64_t sec, min, hour;
> + int64_t millisec = (pts * time_base->num * 1000) / time_base->den;
Use avpriv_set_pts_info() in the write_header function instead. The
rescale will be done internally, and you won't need to pass the time base
along.
> + sec = millisec / 1000;
> + millisec -= 1000 * sec;
> + min = sec / 60;
> + sec -= 60 * min;
> + hour = min / 60;
> + min -= 60 * hour;
> +
> +#if 1
> + // TODO(matthewjheaney at google.com): the timestamp parsing in webvttdec.c
> + // is broken, so for now just output a timestamp in the format we can read.
> + avio_printf(pb, "%ld:%02ld:%02ld.%03ld", hour, min, sec, millisec);
I'm not sure how "broken" the TS parsing in our demuxer is, but this code
certainly is simpler (and thus preferred) than the following anyway...
> +#else
> + if (hour > 0) {
> + avio_printf(pb, "%ld:%02ld:%02ld", hour, min, sec);
> + } else if (min > 0) {
> + avio_printf(pb, "%ld:%02ld", min, sec);
> + } else {
> + avio_printf(pb, "%ld", sec);
> + }
> +
> + if (millisec > 0) {
> + avio_printf(pb, ".%03ld", millisec);
> + }
> +#endif
> +}
> +
> +static int webvtt_write_header(AVFormatContext *ctx)
> +{
> + AVIOContext *pb = ctx->pb;
> + const char header[] = "WEBVTT\n";
> +
> + avio_write(pb, header, strlen(header));
or just avio_printf("WEBVTT\n")
> + avio_flush(pb);
> +
> + return 0;
> +}
> +
> +static int webvtt_write_packet(AVFormatContext *ctx, AVPacket *pkt)
> +{
> + AVStream *s = ctx->streams[0];
> + AVIOContext *pb = ctx->pb;
> + const char space[] = " ";
> + const char EOL[] = "\n";
> + const char arrow[] = "-->";
> + int id_size, settings_size;
> + uint8_t *id, *settings;
> +
> + // Write cue separator.
> +
> + avio_write(pb, EOL, 1);
> +
> + // Write cue id (but only if present).
> +
> + id_size = 0;
You don't need to init id_size and settings_size if you check for the
output pointer.
> + id = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_IDENTIFIER,
> + &id_size);
> +
> + if (id_size > 0) {
> + avio_write(pb, id, id_size);
> + avio_write(pb, EOL, 1);
> + }
> +
Any reason you sometimes use avio_printf and sometimes a bunch of
successive avio_write?
> + // Write timestamp and (optional) settings.
> +
> + webvtt_write_time(pb, pkt->pts, &s->time_base);
> +
> + avio_write(pb, space, strlen(space));
> + avio_write(pb, arrow, strlen(arrow));
> + avio_write(pb, space, strlen(space));
> +
If you used defines instead of const char array, you could simply
avio_printf(pb, SPACE ARROW SPACE), or a avio_write with a sizeof(X)-1.
> + webvtt_write_time(pb, pkt->pts + pkt->duration, &s->time_base);
> +
> + settings_size = 0;
> + settings = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_SETTINGS,
> + &settings_size);
> +
> + if (settings_size > 0) {
> + avio_write(pb, space, strlen(space));
> + avio_write(pb, settings, settings_size);
> + }
> +
> + avio_write(pb, EOL, 1);
> +
> + // Write cue text.
> +
> + avio_write(pb, pkt->data, pkt->size);
> + avio_write(pb, EOL, 1);
> +
> + return 0;
> +}
> +
> +AVOutputFormat ff_webvtt_muxer = {
> + .name = "webvtt",
> + .long_name = NULL_IF_CONFIG_SMALL("WebVTT subtitle"),
> + .extensions = "vtt",
> + .mime_type = "text/vtt",
> + .priv_data_size = sizeof(WebVTTMuxContext),
> + .subtitle_codec = AV_CODEC_ID_WEBVTT,
> + .write_header = webvtt_write_header,
> + .write_packet = webvtt_write_packet,
> +};
--
Clément B.
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