avconv: Use the mpeg12 private option scan_offset

Introduced in aed7900704

Bug-Id: debian/773055
CC: libav-stable@libav.org
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
Signed-off-by: Anton Khirnov <anton@khirnov.net>
(cherry picked from commit fd665f7f48)
Signed-off-by: Anton Khirnov <anton@khirnov.net>

avconv_opt.c

@@ -1825,7 +1825,7 @@ static int opt_target(void *optctx, const char *opt, const char *arg)
         opt_default(NULL, "maxrate", "2516000");
         opt_default(NULL, "minrate", "0"); // 1145000;
         opt_default(NULL, "bufsize", "1835008"); // 224*1024*8;
-        opt_default(NULL, "flags", "+scan_offset");
+        opt_default(NULL, "scan_offset", "1");
 
 
         opt_default(NULL, "b:a", "224000");