caf: support either old or new style ALAC magic kuki chunk

libavformat/cafdec.c

@@ -121,18 +121,40 @@ static int read_kuki_chunk(AVFormatContext *s, int64_t size)
     } else if (st->codec->codec_id == CODEC_ID_ALAC) {
 #define ALAC_PREAMBLE 12
 #define ALAC_HEADER   36
-        if (size < ALAC_PREAMBLE + ALAC_HEADER) {
+#define ALAC_NEW_KUKI 24
+        uint8_t preamble[12];
+        if (size < ALAC_NEW_KUKI || size > ALAC_PREAMBLE + ALAC_HEADER) {
             av_log(s, AV_LOG_ERROR, "invalid ALAC magic cookie\n");
             avio_skip(pb, size);
             return AVERROR_INVALIDDATA;
         }
-        avio_skip(pb, ALAC_PREAMBLE);
+        avio_read(pb, preamble, ALAC_PREAMBLE);
+
         st->codec->extradata = av_mallocz(ALAC_HEADER + FF_INPUT_BUFFER_PADDING_SIZE);
         if (!st->codec->extradata)
             return AVERROR(ENOMEM);
-        avio_read(pb, st->codec->extradata, ALAC_HEADER);
+
+        /* For the old style cookie, we skip 12 bytes, then read 36 bytes.
+         * The new style cookie only contains the last 24 bytes of what was
+         * 36 bytes in the old style cookie, so we fabricate the first 12 bytes
+         * in that case to maintain compatibility. */
+        if (!memcmp(&preamble[4], "frmaalac", 8)) {
+            if (size < ALAC_PREAMBLE + ALAC_HEADER) {
+                av_log(s, AV_LOG_ERROR, "invalid ALAC magic cookie\n");
+                av_freep(&st->codec->extradata);
+                return AVERROR_INVALIDDATA;
+            }
+            avio_read(pb, st->codec->extradata, ALAC_HEADER);
+            avio_skip(pb, size - ALAC_PREAMBLE - ALAC_HEADER);
+        } else {
+            AV_WB32(st->codec->extradata, 36);
+            memcpy(&st->codec->extradata[4], "alac", 4);
+            AV_WB32(&st->codec->extradata[8], 0);
+            memcpy(&st->codec->extradata[12], preamble, 12);
+            avio_read(pb, &st->codec->extradata[24], ALAC_NEW_KUKI - 12);
+            avio_skip(pb, size - ALAC_NEW_KUKI);
+        }
         st->codec->extradata_size = ALAC_HEADER;
-        avio_skip(pb, size - ALAC_PREAMBLE - ALAC_HEADER);
     } else {
         st->codec->extradata = av_mallocz(size + FF_INPUT_BUFFER_PADDING_SIZE);
         if (!st->codec->extradata)