[FFmpeg-devel] [PATCH] avformat/mov: initial support for emsg box

[Brad Hards]

This adds support for the EventMessage box, which is apparently described in
ISO/IEC 23009-1:2019, and is used for KLV metadata per MISB ST 1910.
See https://www.gwg.nga.mil/misb/docs/standards/ST1910.1.pdf Sect 6.2.1
---
 libavformat/isom.h | 15 ++++++++++++
 libavformat/mov.c  | 61 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/libavformat/isom.h b/libavformat/isom.h
index 5a6d504090..8ea62e91f0 100644
--- a/libavformat/isom.h
+++ b/libavformat/isom.h
@@ -79,6 +79,18 @@ typedef struct MOVDref {
     int16_t nlvl_to, nlvl_from;
 } MOVDref;
 
+typedef struct MOVEmsg {
+    uint8_t version;
+    uint32_t timescale;
+    uint32_t presentation_time_delta; ///< only valid for version 0
+    uint64_t presentation_time; ///< only valid for version 1
+    uint32_t event_duration;
+    uint32_t id;
+    char *scheme_id_uri;
+    char *value;
+    uint8_t *message_data;
+} MOVEmsg;
+
 typedef struct MOVAtom {
     uint32_t type;
     int64_t size; /* total size (excluding the size and type fields) */
@@ -297,6 +309,9 @@ typedef struct MOVContext {
     int32_t movie_display_matrix[3][3]; ///< display matrix from mvhd
     int have_read_mfra_size;
     uint32_t mfra_size;
+    // Event Messages from DASH specification, used in MISB ST 1910
+    unsigned emsg_count;  ///< Number of event messages
+    MOVEmsg *emsg_data; ///< Array of Event Messages
 } MOVContext;
 
 int ff_mp4_read_descr_len(AVIOContext *pb);
diff --git a/libavformat/mov.c b/libavformat/mov.c
index 7805330bf9..22bf0b36ea 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -5318,6 +5318,66 @@ static int mov_read_elst(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     return 0;
 }
 
+static int mov_read_emsg(MOVContext *c, AVIOContext *pb, MOVAtom atom)
+{
+    int err;
+    uint32_t bytes_read_from_atom = 0;
+    size_t num_bytes_in_last_read;
+    MOVEmsg *emsg;
+
+    if ((uint64_t)c->emsg_count+1 >= UINT_MAX / sizeof(*c->emsg_data))
+        return AVERROR_INVALIDDATA;
+    if ((err = av_reallocp_array(&c->emsg_data, c->emsg_count + 1,
+                                 sizeof(*c->emsg_data))) < 0) {
+        c->emsg_count = 0;
+        return err;
+    }
+    emsg = &c->emsg_data[c->emsg_count++];
+
+    emsg->version = avio_r8(pb);
+    bytes_read_from_atom += 1;
+    avio_rb24(pb); /* flags */
+    bytes_read_from_atom += 3;
+    if (emsg->version == 0) {
+        emsg->scheme_id_uri = av_malloc(atom.size + 1);
+        num_bytes_in_last_read = avio_get_str(pb, atom.size, emsg->scheme_id_uri, pb->buffer_size + 1);
+        bytes_read_from_atom += num_bytes_in_last_read;
+        av_realloc(emsg->scheme_id_uri, num_bytes_in_last_read);
+        emsg->value = av_malloc(atom.size + 1);
+        num_bytes_in_last_read = avio_get_str(pb, atom.size, emsg->value, pb->buffer_size + 1);
+        bytes_read_from_atom += num_bytes_in_last_read;
+        av_realloc(emsg->value, num_bytes_in_last_read);
+        emsg->timescale = avio_rb32(pb);
+        bytes_read_from_atom += 4;
+        emsg->presentation_time_delta = avio_rb32(pb);
+        bytes_read_from_atom += 4;
+        emsg->event_duration = avio_rb32(pb);
+        bytes_read_from_atom += 4;
+        emsg->id = avio_rb32(pb);
+        bytes_read_from_atom += 4;
+    } else if (emsg->version == 1) {
+        emsg->timescale = avio_rb32(pb);
+        bytes_read_from_atom += 4;
+        emsg->presentation_time = avio_rb64(pb);
+        bytes_read_from_atom += 8;
+        emsg->event_duration = avio_rb32(pb);
+        bytes_read_from_atom += 4;
+        emsg->id = avio_rb32(pb);
+        bytes_read_from_atom += 4;
+        emsg->scheme_id_uri = av_malloc(atom.size + 1);
+        num_bytes_in_last_read = avio_get_str(pb, atom.size, emsg->scheme_id_uri, pb->buffer_size + 1);
+        bytes_read_from_atom += num_bytes_in_last_read;
+        av_realloc(emsg->scheme_id_uri, num_bytes_in_last_read);
+        emsg->value = av_malloc(atom.size + 1);
+        num_bytes_in_last_read = avio_get_str(pb, atom.size, emsg->value, pb->buffer_size + 1);
+        bytes_read_from_atom += num_bytes_in_last_read;
+        av_realloc(emsg->value, num_bytes_in_last_read);
+    }
+    emsg->message_data = av_malloc(atom.size - bytes_read_from_atom);
+    num_bytes_in_last_read = avio_read(pb, emsg->message_data, atom.size - bytes_read_from_atom);
+    return 0;
+}
+
 static int mov_read_tmcd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 {
     MOVStreamContext *sc;
@@ -6895,6 +6955,7 @@ static const MOVParseTableEntry mov_default_parse_table[] = {
 { MKTAG('d','r','e','f'), mov_read_dref },
 { MKTAG('e','d','t','s'), mov_read_default },
 { MKTAG('e','l','s','t'), mov_read_elst },
+{ MKTAG('e','m','s','g'), mov_read_emsg },
 { MKTAG('e','n','d','a'), mov_read_enda },
 { MKTAG('f','i','e','l'), mov_read_fiel },
 { MKTAG('a','d','r','m'), mov_read_adrm },
-- 
2.27.0