[FFmpeg-devel] [PATCH] Write WebVTT output files

Clément Bœsch ubitux at gmail.com
Wed Jun 12 21:03:06 CEST 2013


On Wed, Jun 12, 2013 at 11:45:27AM -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/
> ---
>  doc/general.texi         |   2 +-
>  libavformat/Makefile     |   1 +
>  libavformat/allformats.c |   2 +-
>  libavformat/version.h    |   2 +-
>  libavformat/webvttenc.c  | 116 +++++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 120 insertions(+), 3 deletions(-)
>  create mode 100644 libavformat/webvttenc.c
> 
> diff --git a/doc/general.texi b/doc/general.texi
> index a83b55e..0cddf9f 100644
> --- a/doc/general.texi
> +++ b/doc/general.texi
> @@ -957,7 +957,7 @@ performance on systems without hardware floating point support).
>  @item TED Talks captions @tab @tab X @tab   @tab X
>  @item VobSub (IDX+SUB) @tab   @tab X @tab   @tab X
>  @item VPlayer          @tab   @tab X @tab   @tab X
> - at item WebVTT           @tab   @tab X @tab   @tab X
> + at item WebVTT           @tab X @tab X @tab   @tab X
>  @item XSUB             @tab   @tab   @tab X @tab X
>  @end multitable
>  
> 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

You should not need lavf/subtitles utils for the muxing; it's only helpers
for demuxing.

>  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..d4a2d27 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -292,7 +292,7 @@ void av_register_all(void)
>      REGISTER_MUXDEMUX(WAV,              wav);
>      REGISTER_DEMUXER (WC3,              wc3);
>      REGISTER_MUXER   (WEBM,             webm);
> -    REGISTER_DEMUXER (WEBVTT,           webvtt);
> +    REGISTER_MUXDEMUX(WEBVTT,           webvtt);
>      REGISTER_DEMUXER (WSAUD,            wsaud);
>      REGISTER_DEMUXER (WSVQA,            wsvqa);
>      REGISTER_MUXDEMUX(WTV,              wtv);
> diff --git a/libavformat/version.h b/libavformat/version.h
> index 8db210e..69e9e2c 100644
> --- a/libavformat/version.h
> +++ b/libavformat/version.h
> @@ -30,7 +30,7 @@
>  #include "libavutil/avutil.h"
>  
>  #define LIBAVFORMAT_VERSION_MAJOR 55
> -#define LIBAVFORMAT_VERSION_MINOR  8
> +#define LIBAVFORMAT_VERSION_MINOR  9
>  #define LIBAVFORMAT_VERSION_MICRO 102
>  
>  #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
> diff --git a/libavformat/webvttenc.c b/libavformat/webvttenc.c
> new file mode 100644
> index 0000000..f0f91a5
> --- /dev/null
> +++ b/libavformat/webvttenc.c
> @@ -0,0 +1,116 @@
> +/*
> + * 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"
> +#include "internal.h"
> +
> +static void webvtt_write_time(AVIOContext *pb, int64_t millisec)
> +{
> +    int64_t sec, min, hour;
> +    sec = millisec / 1000;
> +    millisec -= 1000 * sec;
> +    min = sec / 60;
> +    sec -= 60 * min;
> +    hour = min / 60;
> +    min -= 60 * hour;
> +
> +    if (hour > 0)
> +      avio_printf(pb, "%ld:", hour);
> +

style: 4 space indent

> +    avio_printf(pb, "%02ld:%02ld.%03ld", min, sec, millisec);
> +}
> +
> +static int webvtt_write_header(AVFormatContext *ctx)
> +{
> +    AVStream     *s  = ctx->streams[0];

style: weird vertical align

> +    AVIOContext *pb = ctx->pb;
> +
> +    avpriv_set_pts_info(s, 64, 1, 1000);
> +
> +    avio_printf(pb, "WEBVTT\n");
> +    avio_flush(pb);
> +
> +    return 0;
> +}
> +
> +static int webvtt_write_packet(AVFormatContext *ctx, AVPacket *pkt)
> +{
> +    AVIOContext  *pb = ctx->pb;
> +    int id_size, settings_size;
> +    uint8_t *id, *settings;
> +

> +    // Write cue separator.
> +

I'm not sure those comments are really useful, but feel free to keep them
if you like them.

> +    avio_printf(pb, "\n");
> +
> +    // Write cue id (but only if present).
> +
> +    id = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_IDENTIFIER,
> +                                 &id_size);
> +
> +    if (id != NULL && id_size > 0) {

stylenit: we tend to avoid the explicit NULL, so "if (id && id_size...)"

> +        avio_write(pb, id, id_size);
> +        avio_printf(pb, "\n");
> +    }
> +
> +    // Write timestamp and (optional) settings.
> +
> +    webvtt_write_time(pb, pkt->pts);
> +
> +    avio_printf(pb, " ---> ");
> +
> +    webvtt_write_time(pb, pkt->pts + pkt->duration);
> +
> +    settings_size = 0;
> +    settings = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_SETTINGS,
> +                                       &settings_size);
> +
> +    if (settings != NULL && settings_size > 0) {
> +        avio_printf(pb, " ");
> +        avio_write(pb, settings, settings_size);
> +    }
> +

> +    avio_printf(pb, "\n");
> +
> +    // Write cue text.
> +
> +    avio_write(pb, pkt->data, pkt->size);
> +    avio_printf(pb, "\n");
> +

Maybe simply:
  avio_printf(pb, "\n%.*s\n", pkt->size, pkt->data);

You should be able to apply the same thing for the id and settings print
as well.

(though, check for the behaviour with pkt->size = 0, I don't remember if
that's a special case)

> +    avio_flush(pb);
> +

This is done internally automatically depending on an option, it should
not be present here.

> +    return 0;
> +}
> +
> +AVOutputFormat ff_webvtt_muxer = {
> +    .name              = "webvtt",
> +    .long_name         = NULL_IF_CONFIG_SMALL("WebVTT subtitle"),
> +    .extensions        = "vtt",
> +    .mime_type         = "text/vtt",
> +    .subtitle_codec    = AV_CODEC_ID_WEBVTT,
> +    .write_header      = webvtt_write_header,
> +    .write_packet      = webvtt_write_packet,
> +};

Except those (mostly) nitpicks, the patch should be OK. I'll likely apply
at your next iteration.

Note: it would be nice if you could add a FATE test for this muxer into
tests/fate/subtitles.mak later.

Note2: some developers don't really like the creation of a new thread for
each new patch iteration, so maybe reply in that same thread instead.

-- 
Clément B.
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