avformat/mo: Add experimental demuxing support for Opus in ISO BMFF (MP4).

Based on the draft spec at http://vfrmaniac.fushizen.eu/contents/opus_in_isobmff.html

Signed-off-by: Matthew Gregan <kinetik@flim.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mov.c

@@ -5264,6 +5264,54 @@ static int cenc_filter(MOVContext *c, MOVStreamContext *sc, int64_t index, uint8
     return 0;
 }
 
+static int mov_read_dops(MOVContext *c, AVIOContext *pb, MOVAtom atom)
+{
+    const int OPUS_SEEK_PREROLL_MS = 80;
+    AVStream *st;
+    size_t size;
+    int16_t pre_skip;
+
+    if (c->fc->nb_streams < 1)
+        return 0;
+    st = c->fc->streams[c->fc->nb_streams-1];
+
+    if ((uint64_t)atom.size > (1<<30) || atom.size < 11)
+        return AVERROR_INVALIDDATA;
+
+    /* Check OpusSpecificBox version. */
+    if (avio_r8(pb) != 0) {
+        av_log(c->fc, AV_LOG_ERROR, "unsupported OpusSpecificBox version\n");
+        return AVERROR_INVALIDDATA;
+    }
+
+    /* OpusSpecificBox size plus magic for Ogg OpusHead header. */
+    size = atom.size + 8;
+
+    if (ff_alloc_extradata(st->codecpar, size))
+        return AVERROR(ENOMEM);
+
+    AV_WL32(st->codecpar->extradata, MKTAG('O','p','u','s'));
+    AV_WL32(st->codecpar->extradata + 4, MKTAG('H','e','a','d'));
+    AV_WB8(st->codecpar->extradata + 8, 1); /* OpusHead version */
+    avio_read(pb, st->codecpar->extradata + 9, size - 9);
+
+    /* OpusSpecificBox is stored in big-endian, but OpusHead is
+       little-endian; aside from the preceeding magic and version they're
+       otherwise currently identical.  Data after output gain at offset 16
+       doesn't need to be bytewapped. */
+    pre_skip = AV_RB16(st->codecpar->extradata + 10);
+    AV_WL16(st->codecpar->extradata + 10, pre_skip);
+    AV_WL32(st->codecpar->extradata + 12, AV_RB32(st->codecpar->extradata + 12));
+    AV_WL16(st->codecpar->extradata + 16, AV_RB16(st->codecpar->extradata + 16));
+
+    st->codecpar->initial_padding = pre_skip;
+    st->codecpar->seek_preroll = av_rescale_q(OPUS_SEEK_PREROLL_MS,
+                                              (AVRational){1, 1000},
+                                              (AVRational){1, 48000});
+
+    return 0;
+}
+
 static const MOVParseTableEntry mov_default_parse_table[] = {
 { MKTAG('A','C','L','R'), mov_read_aclr },
 { MKTAG('A','P','R','G'), mov_read_avid },
@@ -5345,6 +5393,7 @@ static const MOVParseTableEntry mov_default_parse_table[] = {
 { MKTAG('d','f','L','a'), mov_read_dfla },
 { MKTAG('s','t','3','d'), mov_read_st3d }, /* stereoscopic 3D video box */
 { MKTAG('s','v','3','d'), mov_read_sv3d }, /* spherical video box */
+{ MKTAG('d','O','p','s'), mov_read_dops },
 { 0, NULL }
 };