[FFmpeg-devel] [PATCH v7 2/5] avformat/rcwtdec: add RCWT Closed Captions demuxer
Andreas Rheinhardt
andreas.rheinhardt at outlook.com
Thu Mar 21 18:12:51 EET 2024
Marth64:
> RCWT (Raw Captions With Time) is a format native to ccextractor,
> a commonly used OSS tool for processing 608/708 Closed Captions (CC).
> RCWT can be used to archive the original extracted CC bitstream.
> The muxer was added in January 2024. In this commit, add the demuxer.
>
> One can now demux RCWT files for rendering in ccaption_dec or interop
> with ccextractor (which produces RCWT). Using the muxer/demuxer combo,
> the CC bits can be kept for processing or rendering with either tool.
> This can be an effective way to backup an original CC stream, including
> format extensions like EIA-708 and overall original presentation.
>
> Signed-off-by: Marth64 <marth64 at proxyid.net>
> ---
> Changelog | 2 +-
> doc/demuxers.texi | 30 ++++++++++
> libavformat/Makefile | 1 +
> libavformat/allformats.c | 1 +
> libavformat/rcwtdec.c | 123 +++++++++++++++++++++++++++++++++++++++
> 5 files changed, 156 insertions(+), 1 deletion(-)
> create mode 100644 libavformat/rcwtdec.c
>
> diff --git a/Changelog b/Changelog
> index e3ca52430c..0ae05c6cce 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -19,7 +19,7 @@ version <next>:
> - lavu/eval: introduce randomi() function in expressions
> - VVC decoder
> - fsync filter
> -- Raw Captions with Time (RCWT) closed caption muxer
> +- RCWT (Raw Captions with Time) Closed Captions muxer and demuxer
> - ffmpeg CLI -bsf option may now be used for input as well as output
> - ffmpeg CLI options may now be used as -/opt <path>, which is equivalent
> to -opt <contents of file <path>>
> diff --git a/doc/demuxers.texi b/doc/demuxers.texi
> index b70f3a38d7..b4c4daacd9 100644
> --- a/doc/demuxers.texi
> +++ b/doc/demuxers.texi
> @@ -1038,6 +1038,36 @@ the command:
> ffplay -f rawvideo -pixel_format rgb24 -video_size 320x240 -framerate 10 input.raw
> @end example
>
> + at anchor{rcwtdec}
> + at section rcwt
> +
> +RCWT (Raw Captions With Time) is a format native to ccextractor, a commonly
> +used open source tool for processing 608/708 Closed Captions (CC) sources.
> +For more information on the format, see @ref{rcwtenc,,,ffmpeg-formats}.
> +
> +This demuxer implements the specification as of March 2024, which has
> +been stable and unchanged since April 2014.
> +
> + at subsection Examples
> +
> + at itemize
> + at item
> +Render Closed Captions to ASS, using the CC decoder (cc_dec):
> + at example
> +ffmpeg -i CC.rcwt.bin CC.ass
> + at end example
> +Note that if your output appears to be empty, you may have to manually
> +set the decoder's @option{data_field} option to pick the desired CC substream.
> +
> + at item
> +Convert an RCWT backup to SCC format, using the SCC muxer (scc):
> + at example
> +ffmpeg -i CC.rcwt.bin -c:s copy CC.scc
> + at end example
> +Note that the SCC format does not support all of the possible CC formats
> +that can be stored in RCWT.
> + at end itemize
> +
> @section sbg
>
> SBaGen script demuxer.
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index 94a949f555..a6de720d8c 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -493,6 +493,7 @@ OBJS-$(CONFIG_QOA_DEMUXER) += qoadec.o
> OBJS-$(CONFIG_R3D_DEMUXER) += r3d.o
> OBJS-$(CONFIG_RAWVIDEO_DEMUXER) += rawvideodec.o
> OBJS-$(CONFIG_RAWVIDEO_MUXER) += rawenc.o
> +OBJS-$(CONFIG_RCWT_DEMUXER) += rcwtdec.o subtitles.o
> OBJS-$(CONFIG_RCWT_MUXER) += rcwtenc.o subtitles.o
> OBJS-$(CONFIG_REALTEXT_DEMUXER) += realtextdec.o subtitles.o
> OBJS-$(CONFIG_REDSPARK_DEMUXER) += redspark.o
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index e15d0fa6d7..3140018f8d 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -391,6 +391,7 @@ extern const FFInputFormat ff_qoa_demuxer;
> extern const FFInputFormat ff_r3d_demuxer;
> extern const FFInputFormat ff_rawvideo_demuxer;
> extern const FFOutputFormat ff_rawvideo_muxer;
> +extern const FFInputFormat ff_rcwt_demuxer;
> extern const FFOutputFormat ff_rcwt_muxer;
> extern const FFInputFormat ff_realtext_demuxer;
> extern const FFInputFormat ff_redspark_demuxer;
> diff --git a/libavformat/rcwtdec.c b/libavformat/rcwtdec.c
> new file mode 100644
> index 0000000000..e5cd05ea3e
> --- /dev/null
> +++ b/libavformat/rcwtdec.c
> @@ -0,0 +1,123 @@
> +/*
> + * RCWT (Raw Captions With Time) demuxer
> + *
> + * 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
> + */
> +
> +/*
> + * RCWT (Raw Captions With Time) is a format native to ccextractor, a commonly
> + * used open source tool for processing 608/708 Closed Captions (CC) sources.
> + *
> + * This demuxer implements the specification as of March 2024, which has
> + * been stable and unchanged since April 2014.
> + *
> + * A free specification of RCWT can be found here:
> + * @url{https://github.com/CCExtractor/ccextractor/blob/master/docs/BINARY_FILE_FORMAT.TXT}
> + */
> +
> +#include "avformat.h"
> +#include "demux.h"
> +#include "internal.h"
> +#include "subtitles.h"
> +#include "libavutil/intreadwrite.h"
> +
> +#define RCWT_HEADER_SIZE 11
> +
> +typedef struct RCWTContext {
> + FFDemuxSubtitlesQueue q;
> +} RCWTContext;
> +
> +static int rcwt_read_header(AVFormatContext *avf)
> +{
> + RCWTContext *rcwt = avf->priv_data;
> +
> + AVStream *st;
> + uint8_t header[RCWT_HEADER_SIZE];
> + int nb_bytes;
> +
> + /* read header */
> + nb_bytes = ffio_read_size(avf->pb, header, RCWT_HEADER_SIZE);
> + if (nb_bytes != RCWT_HEADER_SIZE)
> + return AVERROR_INVALIDDATA;
ret = ffio_read_size()
if (ret < 0)
return ret;
(I dislike that we return AVERROR_INVALIDDATA when a file is truncated;
IMO a dedicated error code for that would be better and if one were ever
introduced, my code above would automatically use if ffio_read_size()
alone is updated.)
> +
> + if (AV_RB16(header + 6) != 0x0001) {
> + av_log(avf, AV_LOG_ERROR, "RCWT format version is not compatible "
> + "(only version 0.001 is known)\n");
> + return AVERROR_INVALIDDATA;
> + }
> +
> + av_log(avf, AV_LOG_DEBUG, "RCWT writer application: %02X version: %02x\n",
> + header[3], header[5]);
> +
> + /* setup stream */
> + st = avformat_new_stream(avf, NULL);
> + if (!st)
> + return AVERROR(ENOMEM);
> +
> + st->codecpar->codec_type = AVMEDIA_TYPE_SUBTITLE;
> + st->codecpar->codec_id = AV_CODEC_ID_EIA_608;
> +
> + avpriv_set_pts_info(st, 64, 1, 1000);
> +
> + /* demux */
> + while (!avio_feof(avf->pb)) {
> + AVPacket *sub;
> + int ret;
> + int64_t cluster_pos = avio_tell(avf->pb);
> + int64_t cluster_pts = avio_rl64(avf->pb);
> + int cluster_nb_blocks = avio_rl16(avf->pb);
> +
> + if (cluster_nb_blocks == 0)
> + continue;
> +
> + sub = ff_subtitles_queue_insert(&rcwt->q, NULL, 0, 0);
> + if (!sub)
> + return AVERROR(ENOMEM);
> +
> + if ((ret = av_get_packet(avf->pb, sub, cluster_nb_blocks * 3)) < 0)
Please avoid the "if ((ret = func()) < 0)" style (see fbf1e5135298b for
why; I am not claiming that your code is affected by this).
> + return ret;
> +
> + sub->pos = cluster_pos;
> + sub->pts = cluster_pts;
> + }
> +
> + ff_subtitles_queue_finalize(avf, &rcwt->q);
> +
> + return 0;
> +}
> +
> +static int rcwt_probe(const AVProbeData *p)
> +{
> + return p->buf_size > RCWT_HEADER_SIZE &&
> + AV_RB16(p->buf) == 0xCCCC &&
> + AV_RB8(p->buf + 2) == 0xED &&
> + AV_RB16(p->buf + 6) == 0x0001 ? 50 : 0;
> +}
> +
> +const FFInputFormat ff_rcwt_demuxer = {
> + .p.name = "rcwt",
> + .p.long_name = NULL_IF_CONFIG_SMALL("RCWT (Raw Captions With Time)"),
> + .p.extensions = "bin",
> + .p.flags = AVFMT_TS_DISCONT,
> + .priv_data_size = sizeof(RCWTContext),
> + .flags_internal = FF_FMT_INIT_CLEANUP,
> + .read_probe = rcwt_probe,
> + .read_header = rcwt_read_header,
> + .read_packet = ff_subtitles_read_packet,
> + .read_seek2 = ff_subtitles_read_seek,
> + .read_close = ff_subtitles_read_close
> +};
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