avoid too many false detections

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@1537 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/mpeg.c

@@ -405,15 +405,19 @@ static int mpeg_mux_end(AVFormatContext *ctx)
 
 static int mpegps_probe(AVProbeData *p)
 {
-    int code, c, i;
-    code = 0xff;
+    int code;
+    const uint8_t *d;
 
     /* we search the first start code. If it is a packet start code,
        then we decide it is mpeg ps. We do not send highest value to
        give a chance to mpegts */
-    for(i=0;i<p->buf_size;i++) {
-        c = p->buf[i];
-        code = (code << 8) | c;
+    /* NOTE: the search range was restricted to avoid too many false
+       detections */
+
+    if (p->buf_size < 6)
+        return 0;
+    d = p->buf;
+    code = (d[0] << 24) | (d[1] << 16) | (d[2] << 8) | (d[3]);
     if ((code & 0xffffff00) == 0x100) {
         if (code == PACK_START_CODE ||
             code == SYSTEM_HEADER_START_CODE ||
@@ -427,7 +431,6 @@ static int mpegps_probe(AVProbeData *p)
         else
             return 0;
     }
-    }
     return 0;
 }
 

libavformat/raw.c

@@ -153,15 +153,19 @@ static int video_read_header(AVFormatContext *s,
 /* XXX: improve that by looking at several start codes */
 static int mpegvideo_probe(AVProbeData *p)
 {
-    int code, c, i;
-    code = 0xff;
+    int code;
+    const uint8_t *d;
 
     /* we search the first start code. If it is a sequence, gop or
        picture start code then we decide it is an mpeg video
        stream. We do not send highest value to give a chance to mpegts */
-    for(i=0;i<p->buf_size;i++) {
-        c = p->buf[i];
-        code = (code << 8) | c;
+    /* NOTE: the search range was restricted to avoid too many false
+       detections */
+
+    if (p->buf_size < 6)
+        return 0;
+    d = p->buf;
+    code = (d[0] << 24) | (d[1] << 16) | (d[2] << 8) | (d[3]);
     if ((code & 0xffffff00) == 0x100) {
         if (code == SEQ_START_CODE ||
             code == GOP_START_CODE ||
@@ -170,7 +174,6 @@ static int mpegvideo_probe(AVProbeData *p)
         else
             return 0;
     }
-    }
     return 0;
 }