[FFmpeg-devel] [PATCH v5] Add SUP/PGS subtitle demuxer

[Petri Hintukainen]

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:

If DTS is discarded, a.sup and b.sup won't be identical after
  ffmpeg -i a.sup -c:s copy b.sup

DTS is required for some segments in BluRay .m2ts streams. If DTS is
dropped, muxing to .m2ts does not produce BluRay compliant stream.

XBMC seems to require DTS in PGS streams:
  http://forum.doom9.org/showthread.php?t=152289
(the post is relatively old, I don't know if it has been changed since
then)


The samples do not have DTS because of eac3to does not set it. Files
generated with tsMuxeR should have proper DTS.

> +    if ((ret = av_get_packet(s->pb, pkt, 3)) < 0)
> +        return ret;
> +
> +    pkt->stream_index = 0;
> +    pkt->flags |= AV_PKT_FLAG_KEY;
> +    pkt->pos = pos;
> +    pkt->pts = pts;
> +
> +    if (pkt->size >= 3) {
> +        // The full packet size is stored as part of the packet.
> +        size_t len = AV_RB16(pkt->data + 1);
> +
> +        if ((ret = av_append_packet(s->pb, pkt, len)) < 0)
> +            return ret;
> +    }
> +
> +    return 0;
> +}
> +
> +static int sup_probe(AVProbeData *p)
> +{
> +    unsigned char *buf = p->buf;
> +    size_t buf_size = p->buf_size;
> +    int nb_packets;
> +
> +    for (nb_packets = 0; nb_packets < 10; nb_packets++) {
> +        size_t full_packet_size;
> +        if (buf_size < 10 + 3)
> +            break;
> +        if (AV_RB16(buf) != SUP_PGS_MAGIC)
> +            return 0;
> +        full_packet_size = AV_RB16(buf + 10 + 1) + 10 + 3;
> +        if (buf_size < full_packet_size)
> +            break;
> +        buf += full_packet_size;
> +        buf_size -= full_packet_size;
> +    }
> +    if (!nb_packets)
> +        return 0;
> +    if (nb_packets < 2)
> +        return AVPROBE_SCORE_RETRY / 2;
> +    if (nb_packets < 4)
> +        return AVPROBE_SCORE_RETRY;
> +    if (nb_packets < 10)
> +        return AVPROBE_SCORE_RETRY + 1;
> +    return AVPROBE_SCORE_MAX;
> +}
> +
> +AVInputFormat ff_sup_demuxer = {
> +    .name           = "sup",
> +    .long_name      = NULL_IF_CONFIG_SMALL("raw HDMV Presentation Graphic Stream subtitles"),
> +    .extensions     = "sup",
> +    .mime_type      = "application/x-pgs",
> +    .read_probe     = sup_probe,
> +    .read_header    = sup_read_header,
> +    .read_packet    = sup_read_packet,
> +    .flags          = AVFMT_GENERIC_INDEX,
> +};