avformat/mp3dec: Check for occurances of headers within frames during probing

Fixes misdetection of zYLx.wav

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mp3dec.c

@@ -71,7 +71,7 @@ static int mp3_read_probe(const AVProbeData *p)
     int frames, ret;
     int framesizes, max_framesizes;
     uint32_t header;
-    const uint8_t *buf, *buf0, *buf2, *end;
+    const uint8_t *buf, *buf0, *buf2, *buf3, *end;
 
     buf0 = p->buf;
     end = p->buf + p->buf_size - sizeof(uint32_t);
@@ -86,11 +86,19 @@ static int mp3_read_probe(const AVProbeData *p)
         buf2 = buf;
         for (framesizes = frames = 0; buf2 < end; frames++) {
             MPADecodeHeader h;
+            int header_emu = 0;
 
             header = AV_RB32(buf2);
             ret = avpriv_mpegaudio_decode_header(&h, header);
             if (ret != 0 || end - buf2 < h.frame_size)
                 break;
+
+            for (buf3 = buf2 + 4; buf3 < buf2 + h.frame_size; buf3++) {
+                uint32_t next_sync = AV_RB32(buf3);
+                header_emu += (next_sync & MP3_MASK) == (header & MP3_MASK);
+            }
+            if (header_emu > 2)
+                break;
             buf2 += h.frame_size;
             framesizes += h.frame_size;
         }