avcodec/dovi_rpu: implement support for profile 10

Instead of the nal_prefix, this profile inside wraps the RPU inside an
EMDF container, as specified in ETSI TS 102 366. However, this
DV-specific EMDF container is restricted (by the specification) to
a fixed set of hard-coded parameters, which we can effecitvely treat as
a magic byte sequence.

Validated and tested using official Dolby sample files, which
I unfortunately cannot share. However, there are public sample files
available at the merge request link below.

Relevant links:
- https://www.etsi.org/deliver/etsi_ts/102300_102399/102366/01.04.01_60/ts_102366v010401p.pdf
- https://patentimages.storage.googleapis.com/8a/0b/da/28294acaed2182/EP3588964A1.pdf
- https://www.etsi.org/deliver/etsi_ts/103500_103599/103572/01.03.01_60/ts_103572v010301p.pdf
- https://gitlab.com/mbunkus/mkvtoolnix/-/merge_requests/2254

libavcodec/dovi_rpu.c

@@ -174,6 +174,18 @@ static inline int64_t get_se_coef(GetBitContext *gb, const AVDOVIRpuDataHeader *
     return 0; /* unreachable */
 }
 
+static inline unsigned get_variable_bits(GetBitContext *gb, int n)
+{
+    unsigned int value = get_bits(gb, n);
+    int read_more = get_bits1(gb);
+    while (read_more) {
+        value = (value + 1) << n;
+        value |= get_bits(gb, n);
+        read_more = get_bits1(gb);
+    }
+    return value;
+}
+
 #define VALIDATE(VAR, MIN, MAX)                                                 \
     do {                                                                        \
         if (VAR < MIN || VAR > MAX) {                                           \
@@ -200,9 +212,36 @@ int ff_dovi_rpu_parse(DOVIContext *s, const uint8_t *rpu, size_t rpu_size)
     if ((ret = init_get_bits8(gb, rpu, rpu_size)) < 0)
         return ret;
 
-    /* RPU header, common values */
-    nal_prefix = get_bits(gb, 8);
-    VALIDATE(nal_prefix, 25, 25);
+    /* Container header */
+    if (s->dv_profile == 10 /* dav1.10 */) {
+        /* DV inside AV1 re-uses an EMDF container skeleton, but with fixed
+         * values - so we can effectively treat this as a magic byte sequence.
+         *
+         * The exact fields are, as follows:
+         *   emdf_version            : f(2) = 0
+         *   key_id                  : f(3) = 6
+         *   emdf_payload_id         : f(5) = 31
+         *   emdf_payload_id_ext     : var(5) = 225
+         *   smploffste              : f(1) = 0
+         *   duratione               : f(1) = 0
+         *   groupide                : f(1) = 0
+         *   codecdatae              : f(1) = 0
+         *   discard_unknown_payload : f(1) = 1
+         */
+        const unsigned header_magic = 0x01be6841u;
+        unsigned header, emdf_payload_size;
+        header = get_bits_long(gb, 27);
+        VALIDATE(header, header_magic, header_magic);
+        emdf_payload_size = get_variable_bits(gb, 8);
+        VALIDATE(emdf_payload_size, 6, 512);
+        if (emdf_payload_size * 8 > get_bits_left(gb))
+            return AVERROR_INVALIDDATA;
+    } else {
+        nal_prefix = get_bits(gb, 8);
+        VALIDATE(nal_prefix, 25, 25);
+    }
+
+    /* RPU header */
     rpu_type = get_bits(gb, 6);
     if (rpu_type != 2) {
         av_log(s->logctx, AV_LOG_WARNING, "Unrecognized RPU type "