[FFmpeg-devel] [PATCH v5] Add SUP/PGS subtitle demuxer
Petri Hintukainen
phintuka at gmail.com
Mon Sep 1 12:37:23 CEST 2014
On ma, 2014-09-01 at 10:05 +0200, Hendrik Leppkes wrote:
> On Mon, Sep 1, 2014 at 10:01 AM, Petri Hintukainen <phintuka at gmail.com> wrote:
> > On ma, 2014-09-01 at 00:34 +0200, wm4 wrote:
> >> ---
> >> Use AV_RB16 instead of memcpy.
> >> Don't use AVPROBE_SCORE_EXTENSION.
> >> ---
> >> libavformat/Makefile | 1 +
> >> libavformat/allformats.c | 1 +
> >> libavformat/supdec.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++
> >> 3 files changed, 109 insertions(+)
> >> create mode 100644 libavformat/supdec.c
> >>
> >> diff --git a/libavformat/Makefile b/libavformat/Makefile
> >> index 3d124fb..b4965fe 100644
> >> --- a/libavformat/Makefile
> >> +++ b/libavformat/Makefile
> >> @@ -405,6 +405,7 @@ OBJS-$(CONFIG_SRT_MUXER) += srtenc.o
> >> OBJS-$(CONFIG_STR_DEMUXER) += psxstr.o
> >> OBJS-$(CONFIG_SUBVIEWER1_DEMUXER) += subviewer1dec.o subtitles.o
> >> OBJS-$(CONFIG_SUBVIEWER_DEMUXER) += subviewerdec.o subtitles.o
> >> +OBJS-$(CONFIG_SUP_DEMUXER) += supdec.o
> >> OBJS-$(CONFIG_SWF_DEMUXER) += swfdec.o swf.o
> >> OBJS-$(CONFIG_SWF_MUXER) += swfenc.o swf.o
> >> OBJS-$(CONFIG_TAK_DEMUXER) += takdec.o apetag.o img2.o rawdec.o
> >> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> >> index 8f70c4b..e6c0e5f 100644
> >> --- a/libavformat/allformats.c
> >> +++ b/libavformat/allformats.c
> >> @@ -280,6 +280,7 @@ void av_register_all(void)
> >> REGISTER_DEMUXER (STR, str);
> >> REGISTER_DEMUXER (SUBVIEWER1, subviewer1);
> >> REGISTER_DEMUXER (SUBVIEWER, subviewer);
> >> + REGISTER_DEMUXER (SUP, sup);
> >> REGISTER_MUXDEMUX(SWF, swf);
> >> REGISTER_DEMUXER (TAK, tak);
> >> REGISTER_MUXER (TEE, tee);
> >> diff --git a/libavformat/supdec.c b/libavformat/supdec.c
> >> new file mode 100644
> >> index 0000000..3726c97
> >> --- /dev/null
> >> +++ b/libavformat/supdec.c
> >> @@ -0,0 +1,107 @@
> >> +/*
> >> + * 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
> >> + */
> >> +
> >> +#include "avformat.h"
> >> +#include "internal.h"
> >> +#include "libavutil/intreadwrite.h"
> >> +
> >> +#define SUP_PGS_MAGIC 0x5047 /* "PG", big endian */
> >> +
> >> +static int sup_read_header(AVFormatContext *s)
> >> +{
> >> + AVStream *st = avformat_new_stream(s, NULL);
> >> + if (!st)
> >> + return AVERROR(ENOMEM);
> >> + st->codec->codec_type = AVMEDIA_TYPE_SUBTITLE;
> >> + st->codec->codec_id = AV_CODEC_ID_HDMV_PGS_SUBTITLE;
> >> + avpriv_set_pts_info(st, 32, 1, 90000);
> >> +
> >> + return 0;
> >> +}
> >> +
> >> +static int sup_read_packet(struct AVFormatContext *s, AVPacket *pkt)
> >> +{
> >> + int64_t pts, pos;
> >> + int ret;
> >> +
> >> + pos = avio_tell(s->pb);
> >> +
> >> + if (avio_rb16(s->pb) != SUP_PGS_MAGIC)
> >> + return avio_feof(s->pb) ? AVERROR_EOF : AVERROR_INVALIDDATA;
> >> +
> >> + pts = avio_rb32(s->pb);
> >> + avio_rb32(s->pb); /* discard DTS (usually 0, and useless) */
> >
> > Is there some reason to discard DTS ? I would keep DTS when it is
> > present, even if ffmpeg decoder does not use it. There are several
> > reasons why DTS should be kept:
> >
>
> Setting a DTS of 0 for all frames could result in serious problems.
Unless it is set only when > 0 ?
> Shouldn't DTS and PTS be the same for subtitles anyway,
The stream does not carry subtitles, it carries PGS (Presentation
Graphics Stream) segments. Each segment has separate PTS/DTS timestamps.
Subtitle is a result of applying composition rules from two or more
Presentation Composition Segments to the data carried in other
segments.
> considering they are not re-ordered?
In PGS stream DTS is monotonic but PTS is not. Segments are (kind of)
re-ordered after decoding. Here are timestamps of the segments used to
compose two first subtitles in #2208 sample (00038.m2ts):
First subtitle:
SEG 0x16 DTS 000249146 PTS 000255255 // PCS
SEG 0x17 DTS 000249146 PTS 000254978 // WDS
SEG 0x14 DTS 000249146 PTS 000249146 // PDS
SEG 0x15 DTS 000249146 PTS 000249699 // ODS
SEG 0x80 DTS 000249699 PTS 000249699 // EOD
Hide first subtitle:
SEG 0x16 DTS 000607829 PTS 000608107 // PCS
SEG 0x17 DTS 000607829 PTS 000607830 // WDS
SEG 0x80 DTS 000607829 PTS 000607829 // EOD
Second subtitle:
SEG 0x16 DTS 000609547 PTS 000615615 // PCS
SEG 0x17 DTS 000609547 PTS 000615379 // WDS
SEG 0x14 DTS 000609547 PTS 000609547 // PDS
SEG 0x15 DTS 000609547 PTS 000610019 // ODS
SEG 0x80 DTS 000610019 PTS 000610019 // EOD
Hide second subtitle:
SEG 0x16 DTS 000743005 PTS 000743242 // PCS
SEG 0x17 DTS 000743005 PTS 000743006 // WDS
SEG 0x80 DTS 000743005 PTS 000743005 // EOD
Each segment has separate timestamps. PTS of Presentation Composition
Segment is the time when subtitle is displayed or hidden. PTS in
palette / object segments tells when the segment is valid (and available
to be used in compositing).
First segment in the stream is presentation composition segment.
Following window, palette, object... segments must have smaller PTS or
those could not be used when compositing the image.
The format allows quite complex animated presentation graphics at full
HD resolution. Muxing the stream based on PTS only could be fatal for
resource-limited HW player. DTS can also be important to avoid exceeding
max. bit rate when muxing.
- Petri
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