[FFmpeg-devel] [PATCH v6 6/6] decklink_enc: add support for playout of 608 captions in MOV files

[Devin Heitmueller <devin.heitmueller@ltnglobal.com>]

Unlike other cases where the closed captions are embedded in the
video stream as MPEG-2 userdata or H.264 SEI data, with MOV files
the captions are often found on a separate "e608" subtitle track.

Add support for playout of such files, leveraging the new ccfifo
mechanism to ensure that they are embedded into VANC at the correct
rate (since e608 packets often contain batches of multiple 608 pairs).

Note this patch includes a new file named libavdevice/ccfifo.c, which
allows the ccfifo functionality in libavfilter to be reused even if
doing shared builds.  This is the same approach used for log2_tab.c.

Signed-off-by: Devin Heitmueller <dheitmueller@ltnglobal.com>
---
 libavdevice/Makefile          |  1 +
 libavdevice/ccfifo.c          | 24 ++++++++++++++++
 libavdevice/decklink_common.h |  3 ++
 libavdevice/decklink_enc.cpp  | 65 +++++++++++++++++++++++++++++++++++++++++++
 libavdevice/decklink_enc_c.c  |  2 +-
 5 files changed, 94 insertions(+), 1 deletion(-)
 create mode 100644 libavdevice/ccfifo.c

diff --git a/libavdevice/Makefile b/libavdevice/Makefile
index 8a62822..c304492 100644
--- a/libavdevice/Makefile
+++ b/libavdevice/Makefile
@@ -57,6 +57,7 @@ OBJS-$(CONFIG_LIBDC1394_INDEV)           += libdc1394.o
 
 # Objects duplicated from other libraries for shared builds
 SHLIBOBJS-$(CONFIG_DECKLINK_INDEV)       += reverse.o
+SHLIBOBJS-$(CONFIG_DECKLINK_OUTDEV)      += ccfifo.o
 
 # Windows resource file
 SHLIBOBJS-$(HAVE_GNU_WINDRES)            += avdeviceres.o
diff --git a/libavdevice/ccfifo.c b/libavdevice/ccfifo.c
new file mode 100644
index 0000000..9007094
--- /dev/null
+++ b/libavdevice/ccfifo.c
@@ -0,0 +1,24 @@
+/*
+ * CEA-708 Closed Captioning FIFO
+ * Copyright (c) 2023 LTN Global Communications
+ *
+ * Author: Devin Heitmueller <dheitmueller@ltnglobal.com>
+ *
+ * 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 "libavfilter/ccfifo.c"
diff --git a/libavdevice/decklink_common.h b/libavdevice/decklink_common.h
index 088e165..0d33f94 100644
--- a/libavdevice/decklink_common.h
+++ b/libavdevice/decklink_common.h
@@ -31,6 +31,7 @@
 
 extern "C" {
 #include "libavcodec/packet_internal.h"
+#include "libavfilter/ccfifo.h"
 }
 #include "libavutil/thread.h"
 #include "decklink_common_c.h"
@@ -112,6 +113,8 @@ struct decklink_ctx {
     /* Capture buffer queue */
     AVPacketQueue queue;
 
+    AVCCFifo *cc_fifo;      ///< closed captions
+
     /* Streams present */
     int audio;
     int video;
diff --git a/libavdevice/decklink_enc.cpp b/libavdevice/decklink_enc.cpp
index 9f1a8df..22aa80b 100644
--- a/libavdevice/decklink_enc.cpp
+++ b/libavdevice/decklink_enc.cpp
@@ -326,6 +326,25 @@ static int create_s337_payload(AVPacket *pkt, uint8_t **outbuf, int *outsize)
     return 0;
 }
 
+static int decklink_setup_subtitle(AVFormatContext *avctx, AVStream *st)
+{
+    int ret = -1;
+
+    switch(st->codecpar->codec_id) {
+#if CONFIG_LIBKLVANC
+    case AV_CODEC_ID_EIA_608:
+        /* No special setup required */
+        ret = 0;
+        break;
+#endif
+    default:
+        av_log(avctx, AV_LOG_ERROR, "Unsupported subtitle codec specified\n");
+        break;
+    }
+
+    return ret;
+}
+
 av_cold int ff_decklink_write_trailer(AVFormatContext *avctx)
 {
     struct decklink_cctx *cctx = (struct decklink_cctx *)avctx->priv_data;
@@ -352,6 +371,7 @@ av_cold int ff_decklink_write_trailer(AVFormatContext *avctx)
     klvanc_context_destroy(ctx->vanc_ctx);
 #endif
 
+    ff_ccfifo_freep(&ctx->cc_fifo);
     av_freep(&cctx->ctx);
 
     return 0;
@@ -503,6 +523,21 @@ out:
         free(afd_words);
 }
 
+/* Parse any EIA-608 subtitles sitting on the queue, and write packet side data
+   that will later be handled by construct_cc... */
+static void parse_608subs(AVFormatContext *avctx, struct decklink_ctx *ctx, AVPacket *pkt)
+{
+    size_t cc_size = ff_ccfifo_getoutputsize(ctx->cc_fifo);
+    uint8_t *cc_data;
+
+    if (!ff_ccfifo_ccdetected(ctx->cc_fifo))
+        return;
+
+    cc_data = av_packet_new_side_data(pkt, AV_PKT_DATA_A53_CC, cc_size);
+    if (cc_data)
+        ff_ccfifo_injectbytes(ctx->cc_fifo, cc_data, cc_size);
+}
+
 static int decklink_construct_vanc(AVFormatContext *avctx, struct decklink_ctx *ctx,
                                    AVPacket *pkt, decklink_frame *frame,
                                    AVStream *st)
@@ -513,6 +548,7 @@ static int decklink_construct_vanc(AVFormatContext *avctx, struct decklink_ctx *
     if (!ctx->supports_vanc)
         return 0;
 
+    parse_608subs(avctx, ctx, pkt);
     construct_cc(avctx, ctx, pkt, &vanc_lines);
     construct_afd(avctx, ctx, pkt, &vanc_lines, st);
 
@@ -704,6 +740,16 @@ static int decklink_write_audio_packet(AVFormatContext *avctx, AVPacket *pkt)
     return ret;
 }
 
+static int decklink_write_subtitle_packet(AVFormatContext *avctx, AVPacket *pkt)
+{
+    struct decklink_cctx *cctx = (struct decklink_cctx *)avctx->priv_data;
+    struct decklink_ctx *ctx = (struct decklink_ctx *)cctx->ctx;
+
+    ff_ccfifo_extractbytes(ctx->cc_fifo, pkt->data, pkt->size);
+
+    return 0;
+}
+
 extern "C" {
 
 av_cold int ff_decklink_write_header(AVFormatContext *avctx)
@@ -768,12 +814,29 @@ av_cold int ff_decklink_write_header(AVFormatContext *avctx)
         } else if (c->codec_type == AVMEDIA_TYPE_VIDEO) {
             if (decklink_setup_video(avctx, st))
                 goto error;
+        } else if (c->codec_type == AVMEDIA_TYPE_SUBTITLE) {
+            if (decklink_setup_subtitle(avctx, st))
+                goto error;
         } else {
             av_log(avctx, AV_LOG_ERROR, "Unsupported stream type.\n");
             goto error;
         }
     }
 
+    for (n = 0; n < avctx->nb_streams; n++) {
+        AVStream *st = avctx->streams[n];
+        AVCodecParameters *c = st->codecpar;
+
+        if(c->codec_type == AVMEDIA_TYPE_SUBTITLE)
+            avpriv_set_pts_info(st, 64, ctx->bmd_tb_num, ctx->bmd_tb_den);
+    }
+
+    if (!(ctx->cc_fifo = ff_ccfifo_alloc(av_make_q(ctx->bmd_tb_den, ctx->bmd_tb_num), avctx))) {
+        av_log(ctx, AV_LOG_ERROR, "Failure to setup CC FIFO queue\n");
+        ret = AVERROR(ENOMEM);
+        goto error;
+    }
+
     return 0;
 
 error:
@@ -789,6 +852,8 @@ int ff_decklink_write_packet(AVFormatContext *avctx, AVPacket *pkt)
         return decklink_write_video_packet(avctx, pkt);
     else if (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)
         return decklink_write_audio_packet(avctx, pkt);
+    else if (st->codecpar->codec_type == AVMEDIA_TYPE_SUBTITLE)
+        return decklink_write_subtitle_packet(avctx, pkt);
 
     return AVERROR(EIO);
 }
diff --git a/libavdevice/decklink_enc_c.c b/libavdevice/decklink_enc_c.c
index f7e3150..0a3984b 100644
--- a/libavdevice/decklink_enc_c.c
+++ b/libavdevice/decklink_enc_c.c
@@ -77,7 +77,7 @@ const FFOutputFormat ff_decklink_muxer = {
     .p.long_name      = NULL_IF_CONFIG_SMALL("Blackmagic DeckLink output"),
     .p.audio_codec    = AV_CODEC_ID_PCM_S16LE,
     .p.video_codec    = AV_CODEC_ID_WRAPPED_AVFRAME,
-    .p.subtitle_codec = AV_CODEC_ID_NONE,
+    .p.subtitle_codec = AV_CODEC_ID_EIA_608,
     .p.flags          = AVFMT_NOFILE,
     .p.priv_class     = &decklink_muxer_class,
     .get_device_list = ff_decklink_list_output_devices,
-- 
1.8.3.1

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