[downloader:http] add MIME type and signature for .m4v files (#5505)

gallery_dl/downloader/http.py

@@ -401,6 +401,8 @@ MIME_TYPES = {
     "video/webm": "webm",
     "video/ogg" : "ogg",
     "video/mp4" : "mp4",
+    "video/m4v" : "m4v",
+    "video/x-m4v": "m4v",
     "video/quicktime": "mov",
 
     "audio/wav"  : "wav",
@@ -443,7 +445,8 @@ SIGNATURE_CHECKS = {
     "cur" : lambda s: s[0:4] == b"\x00\x00\x02\x00",
     "psd" : lambda s: s[0:4] == b"8BPS",
     "mp4" : lambda s: (s[4:8] == b"ftyp" and s[8:11] in (
-                       b"mp4", b"avc", b"iso", b"M4V")),
+                       b"mp4", b"avc", b"iso")),
+    "m4v" : lambda s: s[4:11] == b"ftypM4V",
     "mov" : lambda s: s[4:12] == b"ftypqt  ",
     "webm": lambda s: s[0:4] == b"\x1A\x45\xDF\xA3",
     "ogg" : lambda s: s[0:4] == b"OggS",

test/test_downloader.py

@@ -303,7 +303,7 @@ SAMPLES = {
     ("mp4" , b"????ftypmp4"),
     ("mp4" , b"????ftypavc1"),
     ("mp4" , b"????ftypiso3"),
-    ("mp4" , b"????ftypM4V"),
+    ("m4v" , b"????ftypM4V"),
     ("mov" , b"????ftypqt  "),
     ("webm", b"\x1A\x45\xDF\xA3"),
     ("ogg" , b"OggS"),