lavf/mccdec: clean up, add support for mcc 2.0 features, and add SMPTE_436M_ANC output stream

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

3 files changed, 325 insertions, 87 deletions

diff --git a/configure b/configure
index 22b0ef944c..ead9fd8185 100755
--- a/configure
+++ b/configure
@@ -3726,6 +3726,7 @@ matroska_audio_muxer_select="matroska_muxer"
 matroska_demuxer_select="riffdec"
 matroska_demuxer_suggest="bzlib zlib"
 matroska_muxer_select="iso_writer mpeg4audio riffenc aac_adtstoasc_bsf pgs_frame_merge_bsf vp9_superframe_bsf"
+mcc_demuxer_select="smpte_436m"
 mlp_demuxer_select="mlp_parser"
 mmf_muxer_select="riffenc"
 mov_demuxer_select="iso_media riffdec"
diff --git a/doc/demuxers.texi b/doc/demuxers.texi
index 016ce6468d..c6b72c3b69 100644
--- a/doc/demuxers.texi
+++ b/doc/demuxers.texi
@@ -855,6 +855,32 @@ Set the sample rate for libopenmpt to output.
 Range is from 1000 to INT_MAX. The value default is 48000.
 @end table
 
+@anchor{mccdec}
+@section mcc
+
+Demuxer for MacCaption MCC files, it supports MCC versions 1.0 and 2.0.
+MCC files store VANC data, which can include closed captions (EIA-608 and CEA-708), ancillary time code, pan-scan data, etc.
+By default, for backward compatibility, the MCC demuxer extracts just the EIA-608 and CEA-708 closed captions and returns a @code{EIA_608} stream, ignoring all other VANC data.
+You can change it to return all VANC data in a @code{SMPTE_436M_ANC} data stream by setting @option{-eia608_extract 0}
+
+@subsection Examples
+
+@itemize
+@item
+Convert a MCC file to Scenarist (SCC) format:
+@example
+ffmpeg -i CC.mcc -c:s copy CC.scc
+@end example
+Note that the SCC format only supports EIA-608, so this will discard all other data such as CEA-708 extensions.
+
+@item
+Merge a MCC file into a MXF file:
+@example
+ffmpeg -i video_and_audio.mxf -eia608_extract 0 -i CC.mcc -c copy -map 0 -map 1 out.mxf
+@end example
+This retains all VANC data and inserts it into the output MXF file as a @code{SMPTE_436M_ANC} data stream.
+@end itemize
+
 @section mov/mp4/3gp
 
 Demuxer for Quicktime File Format & ISO/IEC Base Media File Format (ISO/IEC 14496-12 or MPEG-4 Part 12, ISO/IEC 15444-12 or JPEG 2000 Part 12).
diff --git a/libavformat/mccdec.c b/libavformat/mccdec.c
index 8c0ea09b6b..8a9eff4c2a 100644
--- a/libavformat/mccdec.c
+++ b/libavformat/mccdec.c
@@ -1,6 +1,7 @@
 /*
  * MCC subtitle demuxer
  * Copyright (c) 2020 Paul B Mahol
+ * Copyright (c) 2025 Jacob Lifshay
  *
  * This file is part of FFmpeg.
  *
@@ -22,18 +23,32 @@
 #include "avformat.h"
 #include "demux.h"
 #include "internal.h"
-#include "subtitles.h"
+#include "libavcodec/bytestream.h"
+#include "libavcodec/codec_id.h"
+#include "libavcodec/smpte_436m.h"
 #include "libavutil/avstring.h"
-#include "libavutil/bprint.h"
-#include "libavutil/intreadwrite.h"
+#include "libavutil/avutil.h"
+#include "libavutil/error.h"
+#include "libavutil/internal.h"
+#include "libavutil/log.h"
+#include "libavutil/macros.h"
+#include "libavutil/opt.h"
+#include "libavutil/rational.h"
+#include "libavutil/timecode.h"
+#include "subtitles.h"
+#include <inttypes.h>
+#include <stdbool.h>
+#include <string.h>
 
 typedef struct MCCContext {
+    const AVClass *class;
+    int                   eia608_extract;
     FFDemuxSubtitlesQueue q;
 } MCCContext;
 
 static int mcc_probe(const AVProbeData *p)
 {
-    char buf[28];
+    char         buf[28];
     FFTextReader tr;
 
     ff_text_init_buf(&tr, p->buf, p->buf_size);
@@ -61,21 +76,27 @@ static int convert(uint8_t x)
 }
 
 typedef struct alias {
-    uint8_t key;
-    int len;
+    uint8_t     key;
+    int         len;
     const char *value;
 } alias;
 
+#define CCPAD "\xFA\x0\x0"
+#define CCPAD3 CCPAD CCPAD CCPAD
+
+static const char cc_pad[27] = CCPAD3 CCPAD3 CCPAD3;
+
 static const alias aliases[20] = {
-    { .key = 16, .len =  3, .value = "\xFA\x0\x0", },
-    { .key = 17, .len =  6, .value = "\xFA\x0\x0\xFA\x0\x0", },
-    { .key = 18, .len =  9, .value = "\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0", },
-    { .key = 19, .len = 12, .value = "\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0", },
-    { .key = 20, .len = 15, .value = "\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0", },
-    { .key = 21, .len = 18, .value = "\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0", },
-    { .key = 22, .len = 21, .value = "\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0", },
-    { .key = 23, .len = 24, .value = "\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0", },
-    { .key = 24, .len = 27, .value = "\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0\xFA\x0\x0", },
+    // clang-format off
+    { .key = 16, .len =  3, .value = cc_pad, },
+    { .key = 17, .len =  6, .value = cc_pad, },
+    { .key = 18, .len =  9, .value = cc_pad, },
+    { .key = 19, .len = 12, .value = cc_pad, },
+    { .key = 20, .len = 15, .value = cc_pad, },
+    { .key = 21, .len = 18, .value = cc_pad, },
+    { .key = 22, .len = 21, .value = cc_pad, },
+    { .key = 23, .len = 24, .value = cc_pad, },
+    { .key = 24, .len = 27, .value = cc_pad, },
     { .key = 25, .len =  3, .value = "\xFB\x80\x80", },
     { .key = 26, .len =  3, .value = "\xFC\x80\x80", },
     { .key = 27, .len =  3, .value = "\xFD\x80\x80", },
@@ -87,113 +108,266 @@ static const alias aliases[20] = {
     { .key = 33, .len =  0, .value = NULL, },
     { .key = 34, .len =  0, .value = NULL, },
     { .key = 35, .len =  1, .value = "\x0", },
+    // clang-format on
+};
+
+typedef struct TimeTracker {
+    int64_t    last_ts;
+    int64_t    twenty_four_hr;
+    AVTimecode timecode;
+} TimeTracker;
+
+static int time_tracker_init(TimeTracker *tt, AVStream *st, AVRational rate, void *log_ctx)
+{
+    *tt     = (TimeTracker){ .last_ts = 0 };
+    int ret = av_timecode_init(&tt->timecode, rate, rate.den == 1001 ? AV_TIMECODE_FLAG_DROPFRAME : 0, 0, log_ctx);
+    if (ret < 0)
+        return ret;
+    // wrap pts values at 24hr ourselves since they can be bigger than fits in an int
+    AVTimecode twenty_four_hr;
+    ret = av_timecode_init_from_components(&twenty_four_hr, rate, tt->timecode.flags, 24, 0, 0, 0, log_ctx);
+    if (ret < 0)
+        return ret;
+    tt->twenty_four_hr = twenty_four_hr.start;
+    // timecode uses reciprocal of timebase
+    avpriv_set_pts_info(st, 64, rate.den, rate.num);
+    return 0;
+}
+
+typedef struct MCCTimecode {
+    unsigned hh, mm, ss, ff, field, line_number;
+} MCCTimecode;
+
+static int time_tracker_set_time(TimeTracker *tt, const MCCTimecode *tc, void *log_ctx)
+{
+    AVTimecode last = tt->timecode;
+    int        ret  = av_timecode_init_from_components(&tt->timecode, last.rate, last.flags, tc->hh, tc->mm, tc->ss, tc->ff, log_ctx);
+    if (ret < 0) {
+        tt->timecode = last;
+        return ret;
+    }
+    tt->last_ts -= last.start;
+    tt->last_ts += tt->timecode.start;
+    if (tt->timecode.start < last.start)
+        tt->last_ts += tt->twenty_four_hr;
+    return 0;
+}
+
+struct ValidTimeCodeRate {
+    AVRational  rate;
+    const char *str;
 };
 
+static struct ValidTimeCodeRate valid_time_code_rates[] = {
+    { .rate = { .num = 24, .den = 1 },       .str = "24"   },
+    { .rate = { .num = 25, .den = 1 },       .str = "25"   },
+    { .rate = { .num = 30000, .den = 1001 }, .str = "30DF" },
+    { .rate = { .num = 30, .den = 1 },       .str = "30"   },
+    { .rate = { .num = 50, .den = 1 },       .str = "50"   },
+    { .rate = { .num = 60000, .den = 1001 }, .str = "60DF" },
+    { .rate = { .num = 60, .den = 1 },       .str = "60"   },
+};
+
+static int parse_time_code_rate(AVFormatContext *s, AVStream *st, TimeTracker *tt, const char *time_code_rate)
+{
+    for (size_t i = 0; i < FF_ARRAY_ELEMS(valid_time_code_rates); i++) {
+        const char *after;
+        if (av_stristart(time_code_rate, valid_time_code_rates[i].str, &after) != 0) {
+            bool bad_after = false;
+            for (; *after; after++) {
+                if (!av_isspace(*after)) {
+                    bad_after = true;
+                    break;
+                }
+            }
+            if (bad_after)
+                continue;
+            return time_tracker_init(tt, st, valid_time_code_rates[i].rate, s);
+        }
+    }
+    av_log(s, AV_LOG_FATAL, "invalid mcc time code rate: %s", time_code_rate);
+    return AVERROR_INVALIDDATA;
+}
+
+static int mcc_parse_time_code_part(char **line_left, unsigned *value, unsigned max, const char *after_set)
+{
+    *value = 0;
+    if (!av_isdigit(**line_left))
+        return AVERROR_INVALIDDATA;
+    while (av_isdigit(**line_left)) {
+        unsigned digit = **line_left - '0';
+        *value         = *value * 10 + digit;
+        ++*line_left;
+        if (*value > max)
+            return AVERROR_INVALIDDATA;
+    }
+    unsigned char after = **line_left;
+    if (!after || !strchr(after_set, after))
+        return AVERROR_INVALIDDATA;
+    ++*line_left;
+    return after;
+}
+
+static int mcc_parse_time_code(char **line_left, MCCTimecode *tc)
+{
+    *tc     = (MCCTimecode){ .field = 0, .line_number = 9 };
+    int ret = mcc_parse_time_code_part(line_left, &tc->hh, 23, ":");
+    if (ret < 0)
+        return ret;
+    ret = mcc_parse_time_code_part(line_left, &tc->mm, 59, ":");
+    if (ret < 0)
+        return ret;
+    ret = mcc_parse_time_code_part(line_left, &tc->ss, 59, ":;");
+    if (ret < 0)
+        return ret;
+    ret = mcc_parse_time_code_part(line_left, &tc->ff, 59, ".\t");
+    if (ret < 0)
+        return ret;
+    if (ret == '.') {
+        ret = mcc_parse_time_code_part(line_left, &tc->field, 1, ",\t");
+        if (ret < 0)
+            return ret;
+        if (ret == ',') {
+            ret = mcc_parse_time_code_part(line_left, &tc->line_number, 0xFFFF, "\t");
+            if (ret < 0)
+                return ret;
+        }
+    }
+    if (ret != '\t')
+        return AVERROR_INVALIDDATA;
+    return 0;
+}
+
 static int mcc_read_header(AVFormatContext *s)
 {
-    MCCContext *mcc = s->priv_data;
-    AVStream *st = avformat_new_stream(s, NULL);
-    AVRational rate = {0};
-    int64_t ts, pos;
-    uint8_t out[4096];
-    char line[4096];
+    MCCContext         *mcc = s->priv_data;
+    AVStream           *st  = avformat_new_stream(s, NULL);
+    int64_t             pos;
+    AVSmpte436mCodedAnc coded_anc = {
+        .payload_sample_coding = AV_SMPTE_436M_PAYLOAD_SAMPLE_CODING_8BIT_LUMA,
+    };
+    char         line[4096];
     FFTextReader tr;
-    int ret = 0;
+    int          ret = 0;
 
     ff_text_init_avio(s, &tr, s->pb);
 
     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, 30);
+    if (mcc->eia608_extract) {
+        st->codecpar->codec_type = AVMEDIA_TYPE_SUBTITLE;
+        st->codecpar->codec_id   = AV_CODEC_ID_EIA_608;
+    } else {
+        st->codecpar->codec_type = AVMEDIA_TYPE_DATA;
+        st->codecpar->codec_id   = AV_CODEC_ID_SMPTE_436M_ANC;
+        av_dict_set(&st->metadata, "data_type", "vbi_vanc_smpte_436M", 0);
+    }
 
-    while (!ff_text_eof(&tr)) {
-        int hh, mm, ss, fs, i = 0, j = 0;
-        int start = 12, count = 0;
-        AVPacket *sub;
-        char *lline;
+    TimeTracker tt;
+    ret = time_tracker_init(&tt, st, (AVRational){ .num = 30, .den = 1 }, s);
+    if (ret < 0)
+        return ret;
 
+    while (!ff_text_eof(&tr)) {
+        pos = ff_text_pos(&tr);
         ff_subtitles_read_line(&tr, line, sizeof(line));
         if (!strncmp(line, "File Format=MacCaption_MCC V", 28))
             continue;
         if (!strncmp(line, "//", 2))
             continue;
         if (!strncmp(line, "Time Code Rate=", 15)) {
-            char *rate_str = line + 15;
-            char *df = NULL;
-            int num = -1, den = -1;
-
-            if (rate_str[0]) {
-                num = strtol(rate_str, &df, 10);
-                den = 1;
-                if (df && !av_strncasecmp(df, "DF", 2)) {
-                    av_reduce(&num, &den, num * 1000LL, 1001, INT_MAX);
-                }
-            }
-
-            if (num > 0 && den > 0) {
-                rate = av_make_q(num, den);
-                avpriv_set_pts_info(st, 64, rate.den, rate.num);
-            }
+            ret = parse_time_code_rate(s, st, &tt, line + 15);
+            if (ret < 0)
+                return ret;
+            continue;
+        }
+        if (strchr(line, '='))
+            continue; // skip attributes
+        char *line_left = line;
+        while (av_isspace(*line_left))
+            line_left++;
+        if (!*line_left) // skip empty lines
+            continue;
+        MCCTimecode tc;
+        ret = mcc_parse_time_code(&line_left, &tc);
+        if (ret < 0) {
+            av_log(s, AV_LOG_ERROR, "can't parse mcc time code");
             continue;
         }
 
-        if (av_sscanf(line, "%d:%d:%d:%d", &hh, &mm, &ss, &fs) != 4 || rate.den <= 0)
+        int64_t last_pts = tt.last_ts;
+        ret              = time_tracker_set_time(&tt, &tc, s);
+        if (ret < 0)
             continue;
+        bool merge = last_pts == tt.last_ts;
 
-        ts = av_sat_add64(av_rescale(hh * 3600LL + mm * 60LL + ss, rate.num, rate.den), fs);
+        coded_anc.line_number   = tc.line_number;
+        coded_anc.wrapping_type = tc.field ? AV_SMPTE_436M_WRAPPING_TYPE_VANC_FIELD_2 : AV_SMPTE_436M_WRAPPING_TYPE_VANC_FRAME;
 
-        lline = (char *)&line;
-        lline += 12;
-        pos = ff_text_pos(&tr);
+        PutByteContext pb;
+        bytestream2_init_writer(&pb, coded_anc.payload, AV_SMPTE_436M_CODED_ANC_PAYLOAD_CAPACITY);
 
-        while (lline[i]) {
-            uint8_t v = convert(lline[i]);
+        while (*line_left) {
+            uint8_t v = convert(*line_left++);
 
             if (v >= 16 && v <= 35) {
                 int idx = v - 16;
-                if (aliases[idx].len) {
-                    if (j >= sizeof(out) - 1 - aliases[idx].len) {
-                        j = 0;
-                        break;
-                    }
-                    memcpy(out + j, aliases[idx].value, aliases[idx].len);
-                    j += aliases[idx].len;
-                }
+                bytestream2_put_buffer(&pb, aliases[idx].value, aliases[idx].len);
             } else {
                 uint8_t vv;
 
-                if (i + 13 >= sizeof(line) - 1)
-                    break;
-                vv = convert(lline[i + 1]);
-                if (j >= sizeof(out) - 1) {
-                    j = 0;
+                if (!*line_left)
                     break;
-                }
-                out[j++] = vv | (v << 4);
-                i++;
+                vv = convert(*line_left++);
+                bytestream2_put_byte(&pb, vv | (v << 4));
             }
-
-            i++;
         }
-        out[j] = 0;
-
-        if (out[7] & 0x80)
-            start += 4;
-        count = (out[11] & 0x1f) * 3;
-        if (j < start + count + 1)
+        if (pb.eof)
             continue;
-
-        if (!count)
+        // remove trailing ANC checksum byte (not to be confused with the CDP checksum byte),
+        // it's not included in 8-bit sample encodings. see section 6.2 (page 14) of:
+        // https://pub.smpte.org/latest/st436/s436m-2006.pdf
+        bytestream2_seek_p(&pb, -1, SEEK_CUR);
+        coded_anc.payload_sample_count = bytestream2_tell_p(&pb);
+        if (coded_anc.payload_sample_count == 0)
+            continue; // ignore if too small
+        // add padding to align to 4 bytes
+        while (!pb.eof && bytestream2_tell_p(&pb) % 4)
+            bytestream2_put_byte(&pb, 0);
+        if (pb.eof)
             continue;
-        sub = ff_subtitles_queue_insert(&mcc->q, out + start, count, 0);
-        if (!sub)
-            return AVERROR(ENOMEM);
+        coded_anc.payload_array_length = bytestream2_tell_p(&pb);
+
+        AVPacket *sub;
+        if (mcc->eia608_extract) {
+            AVSmpte291mAnc8bit anc;
+            if (av_smpte_291m_anc_8bit_decode(
+                    &anc, coded_anc.payload_sample_coding, coded_anc.payload_sample_count, coded_anc.payload, s)
+                < 0)
+                continue;
+            // reuse line
+            int cc_count = av_smpte_291m_anc_8bit_extract_cta_708(&anc, line, s);
+            if (cc_count < 0) // continue if error or if it's not a closed captions packet
+                continue;
+            int len = cc_count * 3;
+
+            sub = ff_subtitles_queue_insert(&mcc->q, line, len, merge);
+            if (!sub)
+                return AVERROR(ENOMEM);
+        } else {
+            sub = ff_subtitles_queue_insert(&mcc->q, NULL, 0, merge);
+            if (!sub)
+                return AVERROR(ENOMEM);
 
-        sub->pos = pos;
-        sub->pts = ts;
+            ret = av_smpte_436m_anc_append(sub, 1, &coded_anc);
+            if (ret < 0)
+                return ret;
+        }
+
+        sub->pos      = pos;
+        sub->pts      = tt.last_ts;
         sub->duration = 1;
+        continue;
     }
 
     ff_subtitles_queue_finalize(s, &mcc->q);
@@ -201,15 +375,52 @@ static int mcc_read_header(AVFormatContext *s)
     return ret;
 }
 
+static int mcc_read_packet(AVFormatContext *s, AVPacket *pkt)
+{
+    MCCContext *mcc = s->priv_data;
+    return ff_subtitles_queue_read_packet(&mcc->q, pkt);
+}
+
+static int mcc_read_seek(AVFormatContext *s, int stream_index, int64_t min_ts, int64_t ts, int64_t max_ts, int flags)
+{
+    MCCContext *mcc = s->priv_data;
+    return ff_subtitles_queue_seek(&mcc->q, s, stream_index, min_ts, ts, max_ts, flags);
+}
+
+static int mcc_read_close(AVFormatContext *s)
+{
+    MCCContext *mcc = s->priv_data;
+    ff_subtitles_queue_clean(&mcc->q);
+    return 0;
+}
+
+#define OFFSET(x) offsetof(MCCContext, x)
+#define SD AV_OPT_FLAG_SUBTITLE_PARAM | AV_OPT_FLAG_DECODING_PARAM
+// clang-format off
+static const AVOption mcc_options[] = {
+    { "eia608_extract", "extract EIA-608/708 captions from VANC packets", OFFSET(eia608_extract), AV_OPT_TYPE_BOOL, {.i64 = 1}, 0, 1, SD },
+    { NULL },
+};
+// clang-format on
+
+static const AVClass mcc_class = {
+    .class_name = "mcc demuxer",
+    .item_name  = av_default_item_name,
+    .option     = mcc_options,
+    .version    = LIBAVUTIL_VERSION_INT,
+    .category   = AV_CLASS_CATEGORY_DEMUXER,
+};
+
 const FFInputFormat ff_mcc_demuxer = {
     .p.name         = "mcc",
     .p.long_name    = NULL_IF_CONFIG_SMALL("MacCaption"),
     .p.extensions   = "mcc",
+    .p.priv_class   = &mcc_class,
     .priv_data_size = sizeof(MCCContext),
     .flags_internal = FF_INFMT_FLAG_INIT_CLEANUP,
     .read_probe     = mcc_probe,
     .read_header    = mcc_read_header,
-    .read_packet    = ff_subtitles_read_packet,
-    .read_seek2     = ff_subtitles_read_seek,
-    .read_close     = ff_subtitles_read_close,
+    .read_packet    = mcc_read_packet,
+    .read_seek2     = mcc_read_seek,
+    .read_close     = mcc_read_close,
 };