[FFmpeg-devel] [PATCH v9 0/5] RCWT Closed Captions demuxer (v9)

[FFmpeg-devel] [PATCH v9 0/5] RCWT Closed Captions demuxer (v9)

[Marth64]

Since v7/8:
* Simplified demuxer error handling logic
* Fixes buggy change to ff_subtitles_queue_insert()
* Documentation improvements

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

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[FFmpeg-devel] [PATCH v9 1/5] avformat/subtitles: extend ff_subtitles_queue_insert() to support not yet available events

[Marth64]

If ff_subtitles_queue_insert() were 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, allow passing a NULL buffer with 0 length
without attempting to do such operations. 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 | 24 ++++++++++++++++--------
 libavformat/subtitles.h |  2 +-
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/libavformat/subtitles.c b/libavformat/subtitles.c
index 3413763c7b..4742ca0667 100644
--- a/libavformat/subtitles.c
+++ b/libavformat/subtitles.c
@@ -21,6 +21,7 @@
 #include "avformat.h"
 #include "subtitles.h"
 #include "avio_internal.h"
+#include "libavutil/avassert.h"
 #include "libavutil/avstring.h"
 
 void ff_text_init_avio(void *s, FFTextReader *r, AVIOContext *pb)
@@ -111,15 +112,20 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
 {
     AVPacket **subs, *sub;
 
+    if (!event)
+        av_assert1(len == 0);
+
     if (merge && q->nb_subs > 0) {
         /* merge with previous event */
 
         int old_len;
         sub = q->subs[q->nb_subs - 1];
         old_len = sub->size;
-        if (av_grow_packet(sub, len) < 0)
-            return NULL;
-        memcpy(sub->data + old_len, event, len);
+        if (event) {
+            if (av_grow_packet(sub, len) < 0)
+                return NULL;
+            memcpy(sub->data + old_len, event, len);
+        }
     } else {
         /* new event */
 
@@ -133,14 +139,16 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
         sub = av_packet_alloc();
         if (!sub)
             return NULL;
-        if (av_new_packet(sub, len) < 0) {
-            av_packet_free(&sub);
-            return NULL;
+        if (event) {
+            if (av_new_packet(sub, len) < 0) {
+                av_packet_free(&sub);
+                return NULL;
+            }
+            memcpy(sub->data, event, len);
         }
-        subs[q->nb_subs++] = sub;
         sub->flags |= AV_PKT_FLAG_KEY;
         sub->pts = sub->dts = 0;
-        memcpy(sub->data, event, len);
+        subs[q->nb_subs++] = sub;
     }
     return sub;
 }
diff --git a/libavformat/subtitles.h b/libavformat/subtitles.h
index 88665663c5..ad6b96ca6a 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 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
-- 
2.34.1

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[FFmpeg-devel] [PATCH v9 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 934241a965..4587d0d511 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..04293c4813 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 CC to ASS using the built-in decoder:
+@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 Scenarist (SCC) format:
+@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 extensions
+that can be stored in RCWT (such as EIA-708).
+@end itemize
+
 @section sbg
 
 SBaGen script demuxer.
diff --git a/libavformat/Makefile b/libavformat/Makefile
index 44aa485029..5d77cba7f1 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..9b0d60fe35
--- /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           ret;
+
+    /* read header */
+    ret = ffio_read_size(avf->pb, header, RCWT_HEADER_SIZE);
+    if (ret < 0)
+        return ret;
+
+    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;
+        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);
+
+        ret = av_get_packet(avf->pb, sub, cluster_nb_blocks * 3);
+        if (ret < 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 v9 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 f2459ef1d3..e06bc4b734 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 v9 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 a10a8e216f..4161401059 100644
--- a/doc/muxers.texi
+++ b/doc/muxers.texi
@@ -3038,19 +3038,18 @@ 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
@@ -3060,6 +3059,16 @@ 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 v9 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 v9 0/5] RCWT Closed Captions demuxer (v9)

[Marth64]

Ping if possible. The patches still apply. 3 of the 5 patches are
documentation only and the demuxer itself is much smaller now. The muxer
already made it in, so was hoping the demuxer could go too :fingers_crossed:
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Re: [FFmpeg-devel] [PATCH v9 1/5] avformat/subtitles: extend ff_subtitles_queue_insert() to support not yet available events

[Stefano Sabatini]

On date Saturday 2024-03-23 21:25:00 -0500, Marth64 wrote:
> If ff_subtitles_queue_insert() were 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, allow passing a NULL buffer with 0 length
> without attempting to do such operations. 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 | 24 ++++++++++++++++--------
>  libavformat/subtitles.h |  2 +-
>  2 files changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/libavformat/subtitles.c b/libavformat/subtitles.c
> index 3413763c7b..4742ca0667 100644
> --- a/libavformat/subtitles.c
> +++ b/libavformat/subtitles.c
> @@ -21,6 +21,7 @@
>  #include "avformat.h"
>  #include "subtitles.h"
>  #include "avio_internal.h"
> +#include "libavutil/avassert.h"
>  #include "libavutil/avstring.h"
>  
>  void ff_text_init_avio(void *s, FFTextReader *r, AVIOContext *pb)
> @@ -111,15 +112,20 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
>  {
>      AVPacket **subs, *sub;
>  
> +    if (!event)
> +        av_assert1(len == 0);
> +
>      if (merge && q->nb_subs > 0) {
>          /* merge with previous event */
>  
>          int old_len;
>          sub = q->subs[q->nb_subs - 1];
>          old_len = sub->size;
> -        if (av_grow_packet(sub, len) < 0)
> -            return NULL;
> -        memcpy(sub->data + old_len, event, len);
> +        if (event) {
> +            if (av_grow_packet(sub, len) < 0)
> +                return NULL;
> +            memcpy(sub->data + old_len, event, len);
> +        }
>      } else {
>          /* new event */
>  
> @@ -133,14 +139,16 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
>          sub = av_packet_alloc();
>          if (!sub)
>              return NULL;
> -        if (av_new_packet(sub, len) < 0) {
> -            av_packet_free(&sub);
> -            return NULL;
> +        if (event) {
> +            if (av_new_packet(sub, len) < 0) {
> +                av_packet_free(&sub);
> +                return NULL;
> +            }
> +            memcpy(sub->data, event, len);
>          }

> -        subs[q->nb_subs++] = sub;
>          sub->flags |= AV_PKT_FLAG_KEY;
>          sub->pts = sub->dts = 0;
> -        memcpy(sub->data, event, len);

> +        subs[q->nb_subs++] = sub;

is the move needed? (but not blocking)

LGTM otherwise.
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Re: [FFmpeg-devel] [PATCH v9 1/5] avformat/subtitles: extend ff_subtitles_queue_insert() to support not yet available events

[Marth64]

> is the move needed? (but not blocking)
It is not needed, but the code flows better I think in terms of
readability. I think it feels cleaner to say, "set up `sub` then add it to
the array" vs. "set up sub's data, add it to the array, then set up its
other fields". But, I am good either way and on stand by if you request me
to change it.

Thank you for the review.
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Re: [FFmpeg-devel] [PATCH v9 2/5] avformat/rcwtdec: add RCWT Closed Captions demuxer

[Stefano Sabatini]

On date Saturday 2024-03-23 21:25:01 -0500, Marth64 wrote:
> 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 934241a965..4587d0d511 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..04293c4813 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 CC to ASS using the built-in decoder:
> +@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.

this options is for the cc_dec decoder, while this is assuming EIA_608,
am I confused?

> +
> +@item
> +Convert an RCWT backup to Scenarist (SCC) format:
> +@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 extensions
> +that can be stored in RCWT (such as EIA-708).
> +@end itemize
> +
>  @section sbg
>  
[...]

LGTM otherwise, thanks.
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Re: [FFmpeg-devel] [PATCH v9 3/5] avformat/rcwtenc: remove repeated documentation

[Stefano Sabatini]

On date Saturday 2024-03-23 21:25:02 -0500, Marth64 wrote:
> 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 f2459ef1d3..e06bc4b734 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

LGTM, thanks.
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Re: [FFmpeg-devel] [PATCH v9 0/5] RCWT Closed Captions demuxer (v9)

[Stefano Sabatini]

On date Tuesday 2024-03-26 10:29:18 -0500, Marth64 wrote:
> Ping if possible. The patches still apply. 3 of the 5 patches are
> documentation only and the demuxer itself is much smaller now. The muxer
> already made it in, so was hoping the demuxer could go too :fingers_crossed:

I sent a few comments but in general looks good to me, will wait a few
days to see if there are more comments and will push otherwise.
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Re: [FFmpeg-devel] [PATCH v9 1/5] avformat/subtitles: extend ff_subtitles_queue_insert() to support not yet available events

[Andreas Rheinhardt]

Marth64:
> If ff_subtitles_queue_insert() were 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, allow passing a NULL buffer with 0 length
> without attempting to do such operations. 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 | 24 ++++++++++++++++--------
>  libavformat/subtitles.h |  2 +-
>  2 files changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/libavformat/subtitles.c b/libavformat/subtitles.c
> index 3413763c7b..4742ca0667 100644
> --- a/libavformat/subtitles.c
> +++ b/libavformat/subtitles.c
> @@ -21,6 +21,7 @@
>  #include "avformat.h"
>  #include "subtitles.h"
>  #include "avio_internal.h"
> +#include "libavutil/avassert.h"
>  #include "libavutil/avstring.h"
>  
>  void ff_text_init_avio(void *s, FFTextReader *r, AVIOContext *pb)
> @@ -111,15 +112,20 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
>  {
>      AVPacket **subs, *sub;
>  
> +    if (!event)
> +        av_assert1(len == 0);

av_assert1(event || len == 0) will make the assert message more
meaningful and saves a line.

> +
>      if (merge && q->nb_subs > 0) {
>          /* merge with previous event */
>  
>          int old_len;
>          sub = q->subs[q->nb_subs - 1];
>          old_len = sub->size;
> -        if (av_grow_packet(sub, len) < 0)
> -            return NULL;
> -        memcpy(sub->data + old_len, event, len);
> +        if (event) {
> +            if (av_grow_packet(sub, len) < 0)
> +                return NULL;
> +            memcpy(sub->data + old_len, event, len);
> +        }
>      } else {
>          /* new event */
>  
> @@ -133,14 +139,16 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
>          sub = av_packet_alloc();
>          if (!sub)
>              return NULL;
> -        if (av_new_packet(sub, len) < 0) {
> -            av_packet_free(&sub);
> -            return NULL;
> +        if (event) {
> +            if (av_new_packet(sub, len) < 0) {
> +                av_packet_free(&sub);
> +                return NULL;
> +            }
> +            memcpy(sub->data, event, len);
>          }
> -        subs[q->nb_subs++] = sub;
>          sub->flags |= AV_PKT_FLAG_KEY;
>          sub->pts = sub->dts = 0;
> -        memcpy(sub->data, event, len);
> +        subs[q->nb_subs++] = sub;
>      }
>      return sub;
>  }
> diff --git a/libavformat/subtitles.h b/libavformat/subtitles.h
> index 88665663c5..ad6b96ca6a 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 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 v9 0/5] RCWT Closed Captions demuxer (v9)

[Stefano Sabatini]

On date Tuesday 2024-03-26 17:07:01 +0100, Stefano Sabatini wrote:
> On date Tuesday 2024-03-26 10:29:18 -0500, Marth64 wrote:
> > Ping if possible. The patches still apply. 3 of the 5 patches are
> > documentation only and the demuxer itself is much smaller now. The muxer
> > already made it in, so was hoping the demuxer could go too :fingers_crossed:
> 

> I sent a few comments but in general looks good to me, will wait a few
> days to see if there are more comments and will push otherwise.

Marth64: I see an unaddressed comment by Andreas, I'll wait for the
next update before merging.
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Re: [FFmpeg-devel] [PATCH v9 0/5] RCWT Closed Captions demuxer (v9)

[Marth64]

Thanks for checking Stefano, I have been behind a bit. I will follow up
with the fix once possible.
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Re: [FFmpeg-devel] [PATCH v9 0/5] RCWT Closed Captions demuxer (v9)

[Marth64]

Stefano, v10 coming shortly. Thank you!
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