lavc: add smpte436m_to_eia608 bitstream filter

Signed-off-by: Jacob Lifshay <programmerjake@gmail.com>

configure

@@ -3539,6 +3539,7 @@ h264_redundant_pps_bsf_select="cbs_h264"
 hevc_metadata_bsf_select="cbs_h265"
 mjpeg2jpeg_bsf_select="jpegtables"
 mpeg2_metadata_bsf_select="cbs_mpeg2"
+smpte436m_to_eia608_bsf_select="smpte_436m"
 trace_headers_bsf_select="cbs cbs_vp8"
 vp9_metadata_bsf_select="cbs_vp9"
 vvc_metadata_bsf_select="cbs_h266"

doc/bitstream_filters.texi

@@ -948,6 +948,11 @@ ffmpeg -i INPUT -c:a copy -bsf:a setts=pts=DTS out.mkv
 Log basic packet information. Mainly useful for testing, debugging,
 and development.
 
+@section smpte436m_to_eia608
+
+Convert from a @code{SMPTE_436M_ANC} data stream to a @code{EIA_608} stream,
+extracting the closed captions from CTA-708 CDP VANC packets, and ignoring all other data.
+
 @anchor{text2movsub}
 @section text2movsub
 

libavcodec/bitstream_filters.c

@@ -61,6 +61,7 @@ extern const FFBitStreamFilter ff_prores_metadata_bsf;
 extern const FFBitStreamFilter ff_remove_extradata_bsf;
 extern const FFBitStreamFilter ff_setts_bsf;
 extern const FFBitStreamFilter ff_showinfo_bsf;
+extern const FFBitStreamFilter ff_smpte436m_to_eia608_bsf;
 extern const FFBitStreamFilter ff_text2movsub_bsf;
 extern const FFBitStreamFilter ff_trace_headers_bsf;
 extern const FFBitStreamFilter ff_truehd_core_bsf;

libavcodec/bsf/Makefile

@@ -38,6 +38,7 @@ OBJS-$(CONFIG_PRORES_METADATA_BSF)        += bsf/prores_metadata.o
 OBJS-$(CONFIG_REMOVE_EXTRADATA_BSF)       += bsf/remove_extradata.o
 OBJS-$(CONFIG_SETTS_BSF)                  += bsf/setts.o
 OBJS-$(CONFIG_SHOWINFO_BSF)               += bsf/showinfo.o
+OBJS-$(CONFIG_SMPTE436M_TO_EIA608_BSF)    += bsf/smpte436m_to_eia608.o
 OBJS-$(CONFIG_TEXT2MOVSUB_BSF)            += bsf/movsub.o
 OBJS-$(CONFIG_TRACE_HEADERS_BSF)          += bsf/trace_headers.o
 OBJS-$(CONFIG_TRUEHD_CORE_BSF)            += bsf/truehd_core.o

libavcodec/bsf/smpte436m_to_eia608.c

@@ -0,0 +1,89 @@
+/*
+ * MXF SMPTE-436M ANC to EIA-608 bitstream filter
+ * Copyright (c) 2025 Jacob Lifshay
+ *
+ * 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 "bsf.h"
+#include "bsf_internal.h"
+#include "codec_id.h"
+#include "libavcodec/smpte_436m.h"
+#include "libavutil/error.h"
+
+static av_cold int ff_smpte436m_to_eia608_init(AVBSFContext *ctx)
+{
+    ctx->par_out->codec_type = AVMEDIA_TYPE_SUBTITLE;
+    ctx->par_out->codec_id   = AV_CODEC_ID_EIA_608;
+    return 0;
+}
+
+static int ff_smpte436m_to_eia608_filter(AVBSFContext *ctx, AVPacket *out)
+{
+    AVPacket *in;
+    int       ret = ff_bsf_get_packet(ctx, &in);
+    if (ret < 0)
+        return ret;
+
+    AVSmpte436mAncIterator iter;
+    ret = av_smpte_436m_anc_iter_init(&iter, in->data, in->size);
+    if (ret < 0)
+        goto fail;
+    AVSmpte436mCodedAnc coded_anc;
+    while ((ret = av_smpte_436m_anc_iter_next(&iter, &coded_anc)) >= 0) {
+        AVSmpte291mAnc8bit anc;
+        ret = av_smpte_291m_anc_8bit_decode(
+            &anc, coded_anc.payload_sample_coding, coded_anc.payload_sample_count, coded_anc.payload, ctx);
+        if (ret < 0)
+            goto fail;
+        ret = av_smpte_291m_anc_8bit_extract_cta_708(&anc, NULL, ctx);
+        if (ret == AVERROR(EAGAIN))
+            continue;
+        if (ret < 0)
+            goto fail;
+        int cc_count = ret;
+
+        ret = av_new_packet(out, 3 * cc_count);
+        if (ret < 0)
+            goto fail;
+
+        ret = av_packet_copy_props(out, in);
+        if (ret < 0)
+            goto fail;
+
+        // verified it won't fail by running it above
+        av_smpte_291m_anc_8bit_extract_cta_708(&anc, out->data, ctx);
+
+        return 0;
+    }
+    if (ret != AVERROR_EOF)
+        return ret;
+    ret = AVERROR(EAGAIN);
+
+fail:
+    if (ret < 0)
+        av_packet_unref(out);
+    av_packet_free(&in);
+    return ret;
+}
+
+const FFBitStreamFilter ff_smpte436m_to_eia608_bsf = {
+    .p.name      = "smpte436m_to_eia608",
+    .p.codec_ids = (const enum AVCodecID[]){ AV_CODEC_ID_SMPTE_436M_ANC, AV_CODEC_ID_NONE },
+    .init        = ff_smpte436m_to_eia608_init,
+    .filter      = ff_smpte436m_to_eia608_filter,
+};