Improve detection of mov files (video/quicktime).

Fixes detection of mov files produced by Nikon cameras (and probably some
other atypical muxers).

The first 4 bytes of a mov file specify the size of the 'ftyp' atom. While
typically the "Compatible_Brands[]" array contains just the "qt " brand and
the size is 0x14, muxers are free to add an arbitrary number of brand markers,
changing the size. For example, Nikon cameras add the brand "niko".

See https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap1/qtff1.html#//apple_ref/doc/uid/TP40000939-CH203-39017

src/matchers/video.rs

@@ -48,14 +48,8 @@ pub fn is_webm(buf: &[u8]) -> bool {
 /// Returns whether a buffer is Quicktime MOV video data.
 pub fn is_mov(buf: &[u8]) -> bool {
     buf.len() > 15
-        && ((buf[0] == 0x0
-            && buf[1] == 0x0
-            && buf[2] == 0x0
-            && buf[3] == 0x14
-            && buf[4] == 0x66
-            && buf[5] == 0x74
-            && buf[6] == 0x79
-            && buf[7] == 0x70)
+        && (((buf[4] == b'f' && buf[5] == b't' && buf[6] == b'y' && buf[7] == b'p')
+            && (buf[8] == b'q' && buf[9] == b't' && buf[10] == b' ' && buf[11] == b' '))
             || (buf[4] == 0x6d && buf[5] == 0x6f && buf[6] == 0x6f && buf[7] == 0x76)
             || (buf[4] == 0x6d && buf[5] == 0x64 && buf[6] == 0x61 && buf[7] == 0x74)
             || (buf[12] == 0x6d && buf[13] == 0x64 && buf[14] == 0x61 && buf[15] == 0x74))

tests/video.rs

@@ -7,6 +7,7 @@ test_format!(Video, "video/x-matroska", "mkv", mkv, "sample.mkv");
 test_format!(Video, "video/webm", "webm", webm, "sample.webm");
 
 test_format!(Video, "video/quicktime", "mov", mov, "sample.mov");
+test_format!(Video, "video/quicktime", "mov", mov2, "sample2.mov");
 
 test_format!(Video, "video/x-msvideo", "avi", avi, "sample.avi");