[FFmpeg-devel] [PATCH] avcodec: add HDMV Text Subtitle decoder
wm4
nfxjfg at googlemail.com
Wed Feb 1 11:35:54 EET 2017
On Wed, 1 Feb 2017 10:23:02 +0100
Paul B Mahol <onemda at gmail.com> wrote:
> On 2/1/17, wm4 <nfxjfg at googlemail.com> wrote:
> > On Wed, 01 Feb 2017 11:05:48 +0200
> > Petri Hintukainen <phintuka at gmail.com> wrote:
> >
> >> ti, 2017-01-31 kello 16:42 +0100, wm4 kirjoitti:
> >> > On Tue, 31 Jan 2017 15:22:17 +0100
> >> > Paul B Mahol <onemda at gmail.com> wrote:
> >> >
> >> > > Signed-off-by: Paul B Mahol <onemda at gmail.com>
> >> > > ---
> >> > > libavcodec/Makefile | 2 +
> >> > > libavcodec/allcodecs.c | 2 +
> >> > > libavcodec/textst_parser.c | 49 ++++++++++++++++++++
> >> > > libavcodec/textstdec.c | 108
> >> > > +++++++++++++++++++++++++++++++++++++++++++++
> >> > > libavformat/utils.c | 1 +
> >> > > 5 files changed, 162 insertions(+)
> >> > > create mode 100644 libavcodec/textst_parser.c
> >> > > create mode 100644 libavcodec/textstdec.c
> >> > >
> >> > > diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> >> > > index 43a6add..edadb0f 100644
> >> > > --- a/libavcodec/Makefile
> >> > > +++ b/libavcodec/Makefile
> >> > > @@ -539,6 +539,7 @@ OBJS-$(CONFIG_SVQ1_ENCODER) +=
> >> > > svq1enc.o svq1.o h263data.o \
> >> > > OBJS-$(CONFIG_SVQ3_DECODER) += svq3.o svq13.o
> >> > > mpegutils.o h264data.o
> >> > > OBJS-$(CONFIG_TEXT_DECODER) += textdec.o ass.o
> >> > > OBJS-$(CONFIG_TEXT_ENCODER) += srtenc.o ass_split.o
> >> > > +OBJS-$(CONFIG_TEXTST_DECODER) += textstdec.o ass.o
> >> > > OBJS-$(CONFIG_TAK_DECODER) += takdec.o tak.o takdsp.o
> >> > > OBJS-$(CONFIG_TARGA_DECODER) += targa.o
> >> > > OBJS-$(CONFIG_TARGA_ENCODER) += targaenc.o rle.o
> >> > > @@ -945,6 +946,7 @@ OBJS-$(CONFIG_RV30_PARSER) +=
> >> > > rv34_parser.o
> >> > > OBJS-$(CONFIG_RV40_PARSER) += rv34_parser.o
> >> > > OBJS-$(CONFIG_SIPR_PARSER) += sipr_parser.o
> >> > > OBJS-$(CONFIG_TAK_PARSER) += tak_parser.o tak.o
> >> > > +OBJS-$(CONFIG_TEXTST_PARSER) += textst_parser.o
> >> > > OBJS-$(CONFIG_VC1_PARSER) += vc1_parser.o vc1.o
> >> > > vc1data.o \
> >> > > simple_idct.o wmv2data.o
> >> > > OBJS-$(CONFIG_VP3_PARSER) += vp3_parser.o
> >> > > diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
> >> > > index f92b2b7..9a90533 100644
> >> > > --- a/libavcodec/allcodecs.c
> >> > > +++ b/libavcodec/allcodecs.c
> >> > > @@ -581,6 +581,7 @@ void avcodec_register_all(void)
> >> > > REGISTER_DECODER(SUBVIEWER, subviewer);
> >> > > REGISTER_DECODER(SUBVIEWER1, subviewer1);
> >> > > REGISTER_ENCDEC (TEXT, text);
> >> > > + REGISTER_DECODER(TEXTST, textst);
> >> > > REGISTER_DECODER(VPLAYER, vplayer);
> >> > > REGISTER_ENCDEC (WEBVTT, webvtt);
> >> > > REGISTER_ENCDEC (XSUB, xsub);
> >> > > @@ -704,6 +705,7 @@ void avcodec_register_all(void)
> >> > > REGISTER_PARSER(RV40, rv40);
> >> > > REGISTER_PARSER(SIPR, sipr);
> >> > > REGISTER_PARSER(TAK, tak);
> >> > > + REGISTER_PARSER(TEXTST, textst);
> >> > > REGISTER_PARSER(VC1, vc1);
> >> > > REGISTER_PARSER(VORBIS, vorbis);
> >> > > REGISTER_PARSER(VP3, vp3);
> >> > > diff --git a/libavcodec/textst_parser.c
> >> > > b/libavcodec/textst_parser.c
> >> > > new file mode 100644
> >> > > index 0000000..5079a96
> >> > > --- /dev/null
> >> > > +++ b/libavcodec/textst_parser.c
> >> > > @@ -0,0 +1,49 @@
> >> > > +/*
> >> > > + * 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
> >> > > + * HDMV TextST subtitle parser
> >> > > + */
> >> > > +
> >> > > +#include "libavutil/intreadwrite.h"
> >> > > +#include "parser.h"
> >> > > +
> >> > > +static int textst_parse(AVCodecParserContext *s1, AVCodecContext
> >> > > *avctx,
> >> > > + const uint8_t **poutbuf, int
> >> > > *poutbuf_size,
> >> > > + const uint8_t *buf, int buf_size)
> >> > > +{
> >> > > + if (buf_size > 13) {
> >> > > + int64_t end;
> >> > > +
> >> > > + s1->pts = ((int64_t)(buf[3] & 1) << 32) |
> >> > > AV_RB32(&buf[4]);
> >> > > + end = ((int64_t)(buf[8] & 1) << 32) | AV_RB32(&buf[9]);
> >> > > + s1->duration = (end - s1->pts);
> >> > > + }
> >> > > +
> >> > > + /* always return the full packet. this parser isn't doing any
> >> > > splitting or
> >> > > + combining, only packet analysis */
> >> > > + *poutbuf = buf;
> >> > > + *poutbuf_size = buf_size;
> >> > > + return buf_size;
> >> > > +}
> >> > > +
> >> > > +AVCodecParser ff_textst_parser = {
> >> > > + .codec_ids = { AV_CODEC_ID_HDMV_TEXT_SUBTITLE },
> >> > > + .parser_parse = textst_parse,
> >> > > +};
> >> >
> >> > Why does it need to be in a parser, instead of the demuxer? It seems
> >> > like this codec exists only in .ts anyway, and the way PTS/duration
> >> > is
> >> > extracted seems very closely tied to the format.
> >>
> >> I think a parser could be good idea, it could be useful when remuxing ?
> >>
> >> In the original BluRay mpeg-ts files this codec uses PES private stream
> >> 2, so there are no timestamps in packets coming from mpeg-ts demuxer.
> >>
> >> Parser could also store the first segment (style segment) in extradata.
> >> I think matroska stores style segment in extradata (not 100% sure, I
> >> don't have such files at hand). This kind of makes sense, it allows
> >> starting playback from middle of the mkv file.
> >>
> >> Maybe parser should not overwrite the timestamps if those are already
> >> present ? I don't know if timestamps in subtitle segments are modified
> >> when muxing to matroska.
> >
> > This codec is supported in mpeg-ts only. There are no hints that it's
> > supported in Matroska. If it were, the parser would break _very_ badly
> > on it when demuxing from mkv too.
>
> It _IS_ supported in matroska as S_HDMV/TEXTST
In that case it's probably a good idea to make the ffmpeg-internal
packet format the same as Matroska's, as they must have found a way to
handle the embedded timestamps in a good way.
But I can't imagine it'd work if your proposed parser is ran on those
Matroska packets.
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