[FFmpeg-devel] [PATCH v4] avformat/rcwtdec: add RCWT Closed Captions demuxer
Marth64
marth64 at proxyid.net
Sun Mar 17 06:29:41 EET 2024
Raw Captions With Time (RCWT) is a format native to ccextractor, a commonly
used open source tool for processing 608/708 Closed Captions (CC) sources.
RCWT can be used to archive the original 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 interoperate
with ccextractor (which produces RCWT). Using the muxer/demuxer combination,
the CC bits can be kept for further processing or rendering with either tool.
This can be an effective approach to backup original CC presentations.
Prior to this, the next best solution was FFmpeg's SCC muxer, but SCC itself
is not compatible with ccextractor (which is a de facto OSS CC processing tool)
and it is a proprietary format.
Tests will follow.
Signed-off-by: Marth64 <marth64 at proxyid.net>
---
libavformat/Makefile | 1 +
libavformat/allformats.c | 1 +
libavformat/rcwtdec.c | 153 +++++++++++++++++++++++++++++++++++++++
3 files changed, 155 insertions(+)
create mode 100644 libavformat/rcwtdec.c
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..1fd35be41b
--- /dev/null
+++ b/libavformat/rcwtdec.c
@@ -0,0 +1,153 @@
+/*
+ * 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.
+ * 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 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_CLUSTER_MAX_BLOCKS 65535
+#define RCWT_BLOCK_SIZE 3
+#define RCWT_HEADER_SIZE 11
+
+typedef struct RCWTContext {
+ FFDemuxSubtitlesQueue q;
+} RCWTContext;
+
+static int rcwt_read_header(AVFormatContext *avf)
+{
+ RCWTContext *rcwt = avf->priv_data;
+
+ AVPacket *sub = NULL;
+ AVStream *st;
+ uint8_t header[RCWT_HEADER_SIZE] = {0};
+ int nb_bytes = 0;
+
+ /* validate the header */
+ nb_bytes = avio_read(avf->pb, header, RCWT_HEADER_SIZE);
+ if (nb_bytes != RCWT_HEADER_SIZE) {
+ av_log(avf, AV_LOG_ERROR, "Header does not have the expected size "
+ "(expected=%d actual=%d)\n",
+ RCWT_HEADER_SIZE, nb_bytes);
+ 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 AVStream */
+ 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)) {
+ int64_t cluster_pts = AV_NOPTS_VALUE;
+ int cluster_nb_blocks = 0;
+ int cluster_size = 0;
+ uint8_t *cluster_buf;
+
+ cluster_pts = avio_rl64(avf->pb);
+ cluster_nb_blocks = avio_rl16(avf->pb);
+ if (cluster_nb_blocks == 0)
+ continue;
+
+ cluster_size = cluster_nb_blocks * RCWT_BLOCK_SIZE;
+ cluster_buf = av_malloc(cluster_size);
+ if (!cluster_buf)
+ return AVERROR(ENOMEM);
+
+ nb_bytes = avio_read(avf->pb, cluster_buf, cluster_size);
+ if (nb_bytes < 0)
+ return nb_bytes;
+
+ if (nb_bytes != cluster_size) {
+ av_freep(&cluster_buf);
+ av_log(avf, AV_LOG_ERROR, "Cluster does not have the expected size "
+ "(expected=%d actual=%d pos=%ld)\n",
+ cluster_size, nb_bytes, avio_tell(avf->pb));
+ return AVERROR_INVALIDDATA;
+ }
+
+ sub = ff_subtitles_queue_insert(&rcwt->q, cluster_buf, cluster_size, 0);
+ if (!sub) {
+ av_freep(&cluster_buf);
+ return AVERROR(ENOMEM);
+ }
+
+ sub->pos = avio_tell(avf->pb);
+ sub->pts = cluster_pts;
+
+ av_freep(&cluster_buf);
+ cluster_buf = NULL;
+ }
+
+ 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 ? 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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