[FFmpeg-devel] [PATCH v7 0/5] RCWT Closed Captions demuxer (meta)

[FFmpeg-devel] [PATCH v7 0/5] RCWT Closed Captions demuxer (meta)

[Marth64]

Since v7:
* Demuxer is simplified, reduced to 92 LOC
* Documentation feedback addressed

Signed-off-by: Marth64 <marth64@proxyid.net>
-- 
2.34.1

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[FFmpeg-devel] [PATCH v7 1/5] avformat/subtitles: extend ff_subtitles_queue_insert() to support empty events

[Marth64]

If ff_subtitles_queue_insert() were to given a NULL buffer
with 0 length, it would still attempt to grow the packet
or memcpy depending on if merge option is enabled.

In this commit, consider a NULL buffer with 0 length as
an empty event and do not attempt to modify the packet.
This way, if a subtitle demuxer happens to pass an empty
cue or wants to use av_get_packet() to read bytes, there
are no unnecessary operations on the packet after it is
allocated.

Signed-off-by: Marth64 <marth64@proxyid.net>
---
 libavformat/subtitles.c | 4 ++++
 libavformat/subtitles.h | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavformat/subtitles.c b/libavformat/subtitles.c
index 3413763c7b..38d2ffb8a9 100644
--- a/libavformat/subtitles.c
+++ b/libavformat/subtitles.c
@@ -117,6 +117,8 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
         int old_len;
         sub = q->subs[q->nb_subs - 1];
         old_len = sub->size;
+        if (event == NULL && len == 0)
+            return sub;
         if (av_grow_packet(sub, len) < 0)
             return NULL;
         memcpy(sub->data + old_len, event, len);
@@ -140,6 +142,8 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
         subs[q->nb_subs++] = sub;
         sub->flags |= AV_PKT_FLAG_KEY;
         sub->pts = sub->dts = 0;
+        if (event == NULL && len == 0)
+            return sub;
         memcpy(sub->data, event, len);
     }
     return sub;
diff --git a/libavformat/subtitles.h b/libavformat/subtitles.h
index 88665663c5..ba162fa503 100644
--- a/libavformat/subtitles.h
+++ b/libavformat/subtitles.h
@@ -112,7 +112,7 @@ typedef struct {
 /**
  * Insert a new subtitle event.
  *
- * @param event the subtitle line, may not be zero terminated
+ * @param event the subtitle line (not zero terminated), or NULL on empty event
  * @param len   the length of the event (in strlen() sense, so without '\0')
  * @param merge set to 1 if the current event should be concatenated with the
  *              previous one instead of adding a new entry, 0 otherwise
-- 
2.34.1

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[FFmpeg-devel] [PATCH v7 2/5] avformat/rcwtdec: add RCWT Closed Captions demuxer

[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@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
 
+@anchor{rcwtdec}
+@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.
+
+@subsection Examples
+
+@itemize
+@item
+Render Closed Captions to ASS, using the CC decoder (cc_dec):
+@example
+ffmpeg -i CC.rcwt.bin CC.ass
+@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.
+
+@item
+Convert an RCWT backup to SCC format, using the SCC muxer (scc):
+@example
+ffmpeg -i CC.rcwt.bin -c:s copy CC.scc
+@end example
+Note that the SCC format does not support all of the possible CC formats
+that can be stored in RCWT.
+@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;
+
+    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)
+            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
+};
-- 
2.34.1

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[FFmpeg-devel] [PATCH v7 3/5] avformat/rcwtenc: remove repeated documentation

[Marth64]

The high level summary of RCWT can be delegated doc/muxers, which
makes it easier to maintain and more consistent with the documentation
of the demuxer.

Signed-off-by: Marth64 <marth64@proxyid.net>
---
 libavformat/rcwtenc.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/libavformat/rcwtenc.c b/libavformat/rcwtenc.c
index ed72de81ef..a1a8c06533 100644
--- a/libavformat/rcwtenc.c
+++ b/libavformat/rcwtenc.c
@@ -21,11 +21,6 @@
 /*
  * 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.
- * It can be used to archive the original, raw CC bitstream and to produce
- * a source file for later CC processing or conversion. As a result,
- * it also allows for interopability with ccextractor for processing CC data
- * extracted via ffmpeg. The format is simple to parse and can be used
- * to retain all lines and variants of CC.
  *
  * This muxer implements the specification as of March 2024, which has
  * been stable and unchanged since April 2014.
-- 
2.34.1

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[FFmpeg-devel] [PATCH v7 4/5] doc/muxers: refresh the RCWT muxer's doc to be consistent with the demuxer

[Marth64]

Signed-off-by: Marth64 <marth64@proxyid.net>
---
 doc/muxers.texi | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/doc/muxers.texi b/doc/muxers.texi
index d9dd72e613..0695a317d4 100644
--- a/doc/muxers.texi
+++ b/doc/muxers.texi
@@ -2987,19 +2987,18 @@ ogg files can be safely chained.
 
 @end table
 
-@anchor{rcwt}
+@anchor{rcwtenc}
 @section rcwt
 
-Raw Captions With Time (RCWT) is a format native to ccextractor, a commonly
-used open source tool for processing 608/708 closed caption (CC) sources.
-It can be used to archive the original, raw CC bitstream and to produce
-a source file for later CC processing or conversion. As a result,
-it also allows for interopability with ccextractor for processing CC data
-extracted via ffmpeg. The format is simple to parse and can be used
-to retain all lines and variants of CC.
+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.
+It can be used to archive the original extracted CC bitstream and to produce
+a source file for later processing or conversion. The format allows
+for interoperability between ccextractor and FFmpeg, is simple to parse,
+and can be used to create a backup of the CC presentation.
 
-This muxer implements the specification as of 2024-01-05, which has
-been stable and unchanged for 10 years as of this writing.
+This muxer implements the specification as of March 2024, which has
+been stable and unchanged since April 2014.
 
 This muxer will have some nuances from the way that ccextractor muxes RCWT.
 No compatibility issues when processing the output with ccextractor
@@ -3009,6 +3008,16 @@ and outputs will not be a bit-exact match.
 A free specification of RCWT can be found here:
 @url{https://github.com/CCExtractor/ccextractor/blob/master/docs/BINARY_FILE_FORMAT.TXT}
 
+@subsection Examples
+
+@itemize
+@item
+Extract Closed Captions to RCWT using lavfi:
+@example
+ffmpeg -f lavfi -i "movie=INPUT.mkv[out+subcc]" -map 0:s:0 -c:s copy CC.rcwt.bin
+@end example
+@end itemize
+
 @anchor{segment}
 @section segment, stream_segment, ssegment
 
-- 
2.34.1

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[FFmpeg-devel] [PATCH v7 5/5] doc/indevs: update CC extraction example to use RCWT muxer

[Marth64]

Signed-off-by: Marth64 <marth64@proxyid.net>
---
 doc/indevs.texi | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/doc/indevs.texi b/doc/indevs.texi
index d1b2bacf8b..fc14737181 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -1069,9 +1069,9 @@ ffplay -f lavfi "movie=test.avi[out0];amovie=test.wav[out1]"
 @end example
 
 @item
-Dump decoded frames to images and closed captions to a file (experimental):
+Dump decoded frames to images and Closed Captions to an RCWT backup:
 @example
-ffmpeg -f lavfi -i "movie=test.ts[out0+subcc]" -map v frame%08d.png -map s -c copy -f rawvideo subcc.bin
+ffmpeg -f lavfi -i "movie=test.ts[out0+subcc]" -map v frame%08d.png -map s -c copy subcc.bin
 @end example
 
 @end itemize
-- 
2.34.1

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Re: [FFmpeg-devel] [PATCH v7 1/5] avformat/subtitles: extend ff_subtitles_queue_insert() to support empty events

[Marth64]

This is in response to the last paragraph of feedback in
https://ffmpeg.org//pipermail/ffmpeg-devel/2024-March/323858.html
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[FFmpeg-devel] [PATCH v8] avformat/rcwtdec: add RCWT Closed Captions demuxer

[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@proxyid.net>
---
 Changelog                |   2 +-
 doc/demuxers.texi        |  30 ++++++++++
 libavformat/Makefile     |   1 +
 libavformat/allformats.c |   1 +
 libavformat/rcwtdec.c    | 125 +++++++++++++++++++++++++++++++++++++++
 5 files changed, 158 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
 
+@anchor{rcwtdec}
+@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.
+
+@subsection Examples
+
+@itemize
+@item
+Render Closed Captions to ASS, using the CC decoder (cc_dec):
+@example
+ffmpeg -i CC.rcwt.bin CC.ass
+@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.
+
+@item
+Convert an RCWT backup to SCC format, using the SCC muxer (scc):
+@example
+ffmpeg -i CC.rcwt.bin -c:s copy CC.scc
+@end example
+Note that the SCC format does not support all of the possible CC formats
+that can be stored in RCWT.
+@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..ca5bdc1940
--- /dev/null
+++ b/libavformat/rcwtdec.c
@@ -0,0 +1,125 @@
+/*
+ * 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 < 0)
+        return nb_bytes;
+    if (nb_bytes != RCWT_HEADER_SIZE)
+        return AVERROR_INVALIDDATA;
+
+    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)
+            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
+};
-- 
2.34.1

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Re: [FFmpeg-devel] [PATCH v7 2/5] avformat/rcwtdec: add RCWT Closed Captions demuxer

[Andreas Rheinhardt]

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@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
>  
> +@anchor{rcwtdec}
> +@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.
> +
> +@subsection Examples
> +
> +@itemize
> +@item
> +Render Closed Captions to ASS, using the CC decoder (cc_dec):
> +@example
> +ffmpeg -i CC.rcwt.bin CC.ass
> +@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.
> +
> +@item
> +Convert an RCWT backup to SCC format, using the SCC muxer (scc):
> +@example
> +ffmpeg -i CC.rcwt.bin -c:s copy CC.scc
> +@end example
> +Note that the SCC format does not support all of the possible CC formats
> +that can be stored in RCWT.
> +@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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Re: [FFmpeg-devel] [PATCH v7 1/5] avformat/subtitles: extend ff_subtitles_queue_insert() to support empty events

[Andreas Rheinhardt]

Marth64:
> If ff_subtitles_queue_insert() were to given a NULL buffer
> with 0 length, it would still attempt to grow the packet
> or memcpy depending on if merge option is enabled.
> 
> In this commit, consider a NULL buffer with 0 length as
> an empty event and do not attempt to modify the packet.
> This way, if a subtitle demuxer happens to pass an empty
> cue or wants to use av_get_packet() to read bytes, there
> are no unnecessary operations on the packet after it is
> allocated.
> 
> Signed-off-by: Marth64 <marth64@proxyid.net>
> ---
>  libavformat/subtitles.c | 4 ++++
>  libavformat/subtitles.h | 2 +-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/libavformat/subtitles.c b/libavformat/subtitles.c
> index 3413763c7b..38d2ffb8a9 100644
> --- a/libavformat/subtitles.c
> +++ b/libavformat/subtitles.c
> @@ -117,6 +117,8 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
>          int old_len;
>          sub = q->subs[q->nb_subs - 1];
>          old_len = sub->size;
> +        if (event == NULL && len == 0)
> +            return sub;

Checks for NULL are typically written as !event. I'd prefer
if (!event) {
    av_assert1(len == 0);
    return sub;
}
as this also makes clear that !event with len > 0 must not happen and
also avoids one runtime check for ordinary users (with assert-level 0).

>          if (av_grow_packet(sub, len) < 0)
>              return NULL;
>          memcpy(sub->data + old_len, event, len);
> @@ -140,6 +142,8 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
>          subs[q->nb_subs++] = sub;
>          sub->flags |= AV_PKT_FLAG_KEY;
>          sub->pts = sub->dts = 0;
> +        if (event == NULL && len == 0)
> +            return sub;
>          memcpy(sub->data, event, len);

This will allocate sub->data to a buffer of size
AV_INPUT_BUFFER_PADDING_SIZE and usable size of zero. This is not what
is intended: You should not allocate anything at all, i.e. skip
av_new_packet().
This small buffer (together with the AVBuffer and AVBufferRef allocated
for it) will leak with your current patch 2.

>      }
>      return sub;
> diff --git a/libavformat/subtitles.h b/libavformat/subtitles.h
> index 88665663c5..ba162fa503 100644
> --- a/libavformat/subtitles.h
> +++ b/libavformat/subtitles.h
> @@ -112,7 +112,7 @@ typedef struct {
>  /**
>   * Insert a new subtitle event.
>   *
> - * @param event the subtitle line, may not be zero terminated
> + * @param event the subtitle line (not zero terminated), or NULL on empty event

on not yet available event

>   * @param len   the length of the event (in strlen() sense, so without '\0')
>   * @param merge set to 1 if the current event should be concatenated with the
>   *              previous one instead of adding a new entry, 0 otherwise

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Re: [FFmpeg-devel] [PATCH v7 1/5] avformat/subtitles: extend ff_subtitles_queue_insert() to support empty events

[Marth64]

Thank you Andreas, for walking me through this in detail.
I will update accordingly and test.
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