Add experimental demuxing support for FLAC in ISO BMFF (MP4).

Based on the draft spec at https://git.xiph.org/?p=flac.git;a=blob;f=doc/isoflac.txtSigned-off-by: Matthew Gregan <kinetik@flim.org>
Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/mov.c

@@ -44,6 +44,7 @@
 #include "libavutil/sha.h"
 #include "libavutil/timecode.h"
 #include "libavcodec/ac3tab.h"
+#include "libavcodec/flac.h"
 #include "libavcodec/mpegaudiodecheader.h"
 #include "avformat.h"
 #include "internal.h"
@@ -4742,6 +4743,43 @@ static int mov_read_saiz(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     return 0;
 }
 
+static int mov_read_dfla(MOVContext *c, AVIOContext *pb, MOVAtom atom)
+{
+    AVStream *st;
+    int last, type, size, ret;
+    uint8_t buf[4];
+
+    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 < 42)
+        return AVERROR_INVALIDDATA;
+
+    /* Check FlacSpecificBox version. */
+    if (avio_r8(pb) != 0)
+        return AVERROR_INVALIDDATA;
+
+    avio_rb24(pb); /* Flags */
+
+    avio_read(pb, buf, sizeof(buf));
+    flac_parse_block_header(buf, &last, &type, &size);
+
+    if (type != FLAC_METADATA_TYPE_STREAMINFO || size != FLAC_STREAMINFO_SIZE) {
+        av_log(c->fc, AV_LOG_ERROR, "STREAMINFO must be first FLACMetadataBlock\n");
+        return AVERROR_INVALIDDATA;
+    }
+
+    ret = ff_get_extradata(c->fc, st->codecpar, pb, size);
+    if (ret < 0)
+        return ret;
+
+    if (!last)
+        av_log(c->fc, AV_LOG_WARNING, "non-STREAMINFO FLACMetadataBlock(s) ignored\n");
+
+    return 0;
+}
+
 static int cenc_filter(MOVContext *c, MOVStreamContext *sc, uint8_t *input, int size)
 {
     uint32_t encrypted_bytes;
@@ -4916,6 +4954,7 @@ static const MOVParseTableEntry mov_default_parse_table[] = {
 { MKTAG('f','r','m','a'), mov_read_frma },
 { MKTAG('s','e','n','c'), mov_read_senc },
 { MKTAG('s','a','i','z'), mov_read_saiz },
+{ MKTAG('d','f','L','a'), mov_read_dfla },
 { 0, NULL }
 };