1
Introduction
During the initial development of MP4Workshop I examined the structure of MP4 files. This document focuses on the atoms/boxes where metadata is stored. The idea behind this document to make things more clear and explain some of the knotty terminology with things often meaning the same (or not).
MP4 or MOV(Quicktime)? What name to use: The MP4 format is based on the Quicktime format[[1]] but from here I will call it MP4 format since this has become more general and they are virtually the same.
2 Dates and data in MP4 files
This whole exercise started with the annoyance of having MP4 files wrongly dated because of wrong time-setting on the recording device and also by noticing strange sorting behavior during sorting in Google Photos and other applications. Simply, the first distinction is between the operating system file attributes (time created, modified, last opened) and the data stored within the MP4 file.
3 Atoms that contain metadata
3.1
Metadata
atom
The ‘meta’ atom, full name ‘metadata atom’ is one
container where metadata is stored in an MP4/MOV file. It can be either a
so-called ‘full atom’ with version and flag bytes added, or a non-full atom
without the latter two. The size of the atom is variable and depends on all the
data inside of it (child atoms).
|
Metadata atom |
|||
|
Variable |
# Bytes |
Type |
Values |
|
Size |
4 |
uint32 |
variable |
|
Type |
4 |
uint32 |
'meta' |
|
Version |
1 |
|
1 |
|
Flags |
3 |
3 bytes |
|
Position in file. The path of metadata atom can be either \moov\meta or \moov\udta\meta, or both. No more than one atom is allowed in each path. The metadata atom can also be present in :[trak ?].
The meta atom
contains many childatoms and data stored in keys. I will not describe the
structure of each separate atom inside as this has been often described
elsewhere, e.g.
Table 1: Example of metadata atom that has no ‘keys’ section. (file had no metadata before, metadata inserted by Windows property editor). Note that metadata atom is a full-atom here. File:[[2]]
|
Metadata atom |
00 |
00 |
00 |
C0 |
6D |
65 |
74 |
61 |
00 |
00 |
00 |
00 |
|||||||||||||||||||||||
|
size |
type |
v |
flags |
||||||||||||||||||||||||||||||||
|
|
|
|
|
meta |
|
|
|
|
|||||||||||||||||||||||||||
|
Metadata handler atom |
00 |
00 |
00 |
21 |
68 |
64 |
6C |
72 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
6D |
64 |
69 |
72 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|||
|
size |
type |
v |
flags |
predefined=0 |
handler type |
Reserved=0 |
Reserved=0 |
Reserved=0 |
Name |
|||||||||||||||||||||||||||
|
|
|
|
|
hdlr |
|
|
|
|
|
|
|
|
mdir |
|
|
|
|
|
|
|
|
|
|
|
|
|
||||||||||
|
Metadata Item List Atom |
00 |
00 |
00 |
93 |
69 |
6C |
73 |
74 |
||||||||||||||||||||||||||||
|
size |
type |
|||||||||||||||||||||||||||||||||||
|
|
|
|
|
ilst |
||||||||||||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
2E |
A9 |
77 |
72 |
74 |
||||||||||||||||||||||||||||
|
size |
type |
|||||||||||||||||||||||||||||||||||
|
|
|
|
|
©wrt |
||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
26 |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
01 |
00 |
00 |
00 |
00 |
57 |
6E |
20 |
63 |
6F |
6D |
70 |
6F |
73 |
65 |
72 |
… |
||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
||||||||||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
Wn
composer1/c.. |
|||||||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
19 |
74 |
6D |
70 |
6F |
||||||||||||||||||||||||||||
|
size |
type |
|||||||||||||||||||||||||||||||||||
|
|
|
|
|
tmpo |
||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
11 |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
15 |
00 |
00 |
00 |
00 |
00 |
|||||||||||||||||||
|
size |
type |
type indicator |
locale indicator |
type=$15=21:
big-endian signed int in 1,2,3 or 4 bytes |
||||||||||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
|
|||||||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
20 |
A9 |
6E |
61 |
6D |
||||||||||||||||||||||||||||
|
size |
type |
|||||||||||||||||||||||||||||||||||
|
|
|
|
|
©nam |
||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
18 |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
01 |
00 |
00 |
00 |
00 |
57 |
69 |
6E |
54 |
69 |
74 |
6C |
65 |
||||||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
||||||||||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
"WinTitle" |
|||||||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
24 |
A9 |
63 |
6D |
74 |
||||||||||||||||||||||||||||
|
size |
type |
|||||||||||||||||||||||||||||||||||
|
|
|
|
|
©cmt |
||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
1C |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
01 |
00 |
00 |
00 |
00 |
57 |
69 |
6E |
20 |
43 |
6F |
6D |
6D |
65 |
6E |
74 |
73 |
||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
|
|
|
|
|
|
|
|
||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
"Win
Comments" |
|
|
|
|
|
|
|
||||||||||||||||||||
Table 2: Example of metadata atom that has a ‘keys’ section. Note that
metadata atom is a non-full-atom here. File: [[3]]
|
Metadata atom |
00 |
00 |
xx |
xx |
6D |
65 |
74 |
61 |
|
||||||||||||||||||||||||||||
|
size |
type |
||||||||||||||||||||||||||||||||||||
|
|
|
|
|
meta |
|||||||||||||||||||||||||||||||||
|
Metadata handler atom |
00 |
00 |
00 |
22 |
68 |
64 |
6C |
72 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
6D |
64 |
74 |
61 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|||
|
size |
type |
v |
flags |
predefined=0 |
handler type |
Reserved=0 |
Reserved=0 |
Reserved=0 |
Name |
||||||||||||||||||||||||||||
|
|
|
|
|
hdlr |
|
|
|
|
|
|
|
|
mdta |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||||||||||
|
Metadata Item Keys
Atom |
00 |
00 |
00 |
93 |
6B |
65 |
79 |
73 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
03 |
|||||||||||||||||||||
|
size |
type |
v |
flags |
entry_count |
|||||||||||||||||||||||||||||||||
|
|
|
|
|
keys |
|
|
|
|
|
|
|
|
|||||||||||||||||||||||||
|
Key value 1 |
00 |
00 |
00 |
28 |
6D |
64 |
74 |
61 |
63 |
6F |
6D |
2E |
61 |
70 |
70 |
6C |
65 |
2E |
71 |
75 |
69 |
63 |
6B |
74 |
69 |
6D |
… |
||||||||||
|
key_size |
key_namespace |
key_name (Apple calls it key_value) |
|||||||||||||||||||||||||||||||||||
|
|
|
|
|
mdta |
com.apple.quicktime.creationdate |
||||||||||||||||||||||||||||||||
|
Key value 2 |
00 |
00 |
00 |
21 |
64 |
61 |
74 |
61 |
63 |
6F |
6D |
2E |
61 |
70 |
70 |
6C |
65 |
2E |
71 |
75 |
69 |
63 |
6B |
74 |
69 |
6D |
… |
||||||||||
|
key_size |
key_namespace |
key_name |
|||||||||||||||||||||||||||||||||||
|
|
|
|
|
mdta |
com.apple.quicktime.model |
||||||||||||||||||||||||||||||||
|
Key value 3 |
00 |
00 |
00 |
24 |
A9 |
6E |
61 |
6D |
63 |
6F |
6D |
2E |
61 |
70 |
70 |
6C |
65 |
2E |
71 |
75 |
69 |
63 |
6B |
74 |
69 |
6D |
… |
||||||||||
|
key_size |
key_namespace |
key_name |
|||||||||||||||||||||||||||||||||||
|
|
|
|
|
mdta |
com.apple.quicktime.location.ISO6709 |
||||||||||||||||||||||||||||||||
|
Metadata Item List
Atom |
00 |
00 |
00 |
xx |
69 |
6C |
73 |
74 |
|||||||||||||||||||||||||||||
|
size |
type |
||||||||||||||||||||||||||||||||||||
|
|
|
|
|
ilst |
|||||||||||||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
30 |
00 |
00 |
00 |
01 |
|||||||||||||||||||||||||||||
|
size |
type |
||||||||||||||||||||||||||||||||||||
|
|
|
|
|
=key 1 |
|||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
28 |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
01 |
46 |
52 |
1A |
41 |
32 |
30 |
31 |
34 |
2D |
30 |
37 |
2D |
30 |
35 |
54 |
… |
|||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
|
|
|
|
|
|
|
||||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
2014-07-05T13:02:04+0200 |
|
|
|
|||||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
21 |
00 |
00 |
00 |
02 |
|||||||||||||||||||||||||||||
|
size |
type |
||||||||||||||||||||||||||||||||||||
|
|
|
|
|
=key 2 |
|||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
19 |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
01 |
46 |
52 |
1A |
41 |
69 |
50 |
68 |
6F |
6E |
65 |
20 |
35 |
73 |
||||||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
|
|
|
|
|||||||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
iPhone
5s |
|
|
|
|
|
|
||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
32 |
00 |
00 |
00 |
03 |
|||||||||||||||||||||||||||||
|
size |
type |
||||||||||||||||||||||||||||||||||||
|
|
|
|
|
=key 3 |
|||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
2A |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
01 |
46 |
52 |
1A |
41 |
2B |
34 |
33 |
2E |
36 |
35 |
32 |
31 |
2B |
30 |
30 |
… |
|||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
|
|
|
|
|
|
|
||||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
+43.6521+003.3638+148.202/ |
|
|
|
|||||||||||||||||||||||||
3.2
User
data atom
A User Data Atom whose immediate parent is a movie atom contains
data relevant to the movie as a whole. Specific tracks can also contain User
Data Atoms, relevant to that specific track. An MP4 file may contain many user
data atoms, but only one user data atom is allowed as the immediate child of
any given movie atom or track atom
The series of atoms inside a User Data Atom is also referred to as ‘user data list’. Each data element in the user data list contains size and type information along with its data. An example is shown in Table 3.
Table 3: Example of user data atom that also contains a meta data atom. File: [[4]]
|
User data atom |
00 |
00 |
01 |
CA |
75 |
64 |
74 |
61 |
|||||||||||||||||||||||||||||
|
size |
type |
||||||||||||||||||||||||||||||||||||
|
|
|
|
|
udta |
|||||||||||||||||||||||||||||||||
|
User data Item Atom |
00 |
00 |
00 |
10 |
53 |
44 |
4C |
4E |
53 |
45 |
51 |
5F |
50 |
4C |
41 |
59 |
|||||||||||||||||||||
|
size |
type |
|
|
|
|
|
|
|
|
||||||||||||||||||||||||||||
|
|
|
|
|
SDLN |
SEQ_PLAY |
|
|
|
|
|
|||||||||||||||||||||||||||
|
User data Item Atom |
00 |
00 |
00 |
10 |
73 |
6D |
72 |
64 |
54 |
52 |
55 |
45 |
42 |
4C |
55 |
45 |
|||||||||||||||||||||
|
size |
type |
|
|
|
|
|
|
|
|
||||||||||||||||||||||||||||
|
|
|
|
|
smrd |
TRUEBLUE |
|
|
|
|
|
|||||||||||||||||||||||||||
|
User data Item Atom |
00 |
00 |
00 |
1E |
A9 |
78 |
79 |
7A |
00 |
12 |
15 |
C7 |
2B |
35 |
30 |
2E |
39 |
36 |
37 |
38 |
2D |
31 |
31 |
34 |
2E |
30 |
36 |
39 |
30 |
2F |
|||||||
|
size |
type |
size |
langua. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||||||||||||||||
|
|
|
|
|
©xyz |
18 |
eng' |
+50.9678-114.0690/ |
|
|
|
|
|
|
|
|
|
|
|
|
|
|||||||||||||||||
|
User data Item Atom |
00 |
00 |
00 |
1A |
73 |
6D |
74 |
61 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
0E |
73 |
61 |
75 |
74 |
00 |
00 |
00 |
00 |
00 |
00 |
|||||||||||
|
size |
type |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||||||||||||||||||||
|
|
|
|
|
smta |
saut |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||||||||||||||||
|
Metadata atom |
00 |
00 |
00 |
97 |
6D |
65 |
74 |
61 |
00 |
00 |
00 |
00 |
|||||||||||||||||||||||||
|
size |
type |
v |
flags |
||||||||||||||||||||||||||||||||||
|
|
|
|
|
meta |
|
|
|
|
|||||||||||||||||||||||||||||
|
Metadata handler atom |
00 |
00 |
00 |
20 |
68 |
64 |
6C |
72 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
6D |
64 |
69 |
72 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|||||
|
size |
type |
v |
flags |
predefined=0 |
handler type |
Reserved=0 |
Reserved=0 |
Reserved=0 |
|||||||||||||||||||||||||||||
|
|
|
|
|
hdlr |
|
|
|
|
|
|
|
|
mdir |
|
|
|
|
|
|
|
|
|
|
|
|
||||||||||||
|
Metadata Item List
Atom |
00 |
00 |
00 |
6B |
69 |
6C |
73 |
74 |
|||||||||||||||||||||||||||||
|
size |
type |
||||||||||||||||||||||||||||||||||||
|
|
|
|
|
ilst |
|||||||||||||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
35 |
A9 |
6E |
61 |
6D |
|||||||||||||||||||||||||||||
|
size |
type |
||||||||||||||||||||||||||||||||||||
|
|
|
|
|
©nam |
|||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
2D |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
01 |
00 |
00 |
00 |
00 |
41 |
6E |
64 |
72 |
6F |
69 |
64 |
20 |
36 |
2E |
.. |
.. |
|||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
|
|
|
|
|
|
|
|
|||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
"Android
6.0.1 tags by Windows" |
|
|
|
|
||||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
2E |
A9 |
63 |
6D |
74 |
|||||||||||||||||||||||||||||
|
size |
type |
||||||||||||||||||||||||||||||||||||
|
|
|
|
|
©cmt |
|||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
26 |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
01 |
00 |
00 |
00 |
00 |
63 |
6F |
6D |
6D |
65 |
6E |
74 |
20 |
73 |
68 |
.. |
.. |
|||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
|
|
|
|
|
|
|
|
|||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
"comment
should be here" |
|
|
|
|
|
|
||||||||||||||||||||||
A User Data Atom can also be the container of a Meta Data Atom as
is shown in Table 3.
Now, an important part that is different from the data inside the Meta
Data Atom (that also can contain atomtypes starting with ©) is the following:
All user data list entries whose type begins with the © character (ASCII 169) are defined to be international text. These list entries must contain a list of text strings with associated language codes. By storing multiple versions of the same text, a single user data text item can contain translations for different languages. The list of text strings uses a small integer atom format, which is identical to the QuickTime atom format, except that it uses 16-bit values for size and type instead of 32-bit values. The first value is the size of the string, including the size and type*, and the second value is the language code for the string.
What is meant is probably the following: In the ‘Quicktime atom format’ (Table 3c) the data is stored in a Value Atom with type ‘data’ including a 4-byte type indicator (1 for string) and a 4-byte locale indicator. When you reshuffle the bytes of the User Data Item Atom you can place the data in a ‘pseudo’ Value Atom like in (Table 3b).
*The first value is the size of the string, including the size and type: type indicator is 1 by definition, type of atom is ‘data’ by definition.
|
a.
atom rooted in \udta\ |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
User data Item Atom |
00 |
00 |
00 |
1E |
A9 |
78 |
79 |
7A |
00 |
12 |
15 |
C7 |
2B |
35 |
30 |
2E |
39 |
36 |
37 |
38 |
2D |
31 |
31 |
34 |
2E |
30 |
36 |
39 |
30 |
2F |
||||||||||||||||||||||||||
|
size |
type |
size |
langua. |
|
||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
©xyz |
18 |
eng' |
+50.9678-114.0690/ |
|||||||||||||||||||||||||||||||||||||||||||||||||
|
b.
same atom rooted in \udta\ , but data reorganised to match pattern of
'Quicktime atom format' shown under c. |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
User data Item Atom |
00 |
00 |
00 |
1E |
A9 |
78 |
79 |
7A |
||||||||||||||||||||||||||||||||||||||||||||||||
|
size |
type |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
©xyz |
||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Pseudo Value atom |
- |
- |
00 |
12 |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
15 |
C7 |
2B |
35 |
30 |
2E |
39 |
36 |
37 |
38 |
2D |
31 |
.. |
.. |
||||||||||||||||||||||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
'data' by defin. |
1 by defin. |
|
+50.9678-114.0690/ |
|
|||||||||||||||||||||||||||
|
c.
another atom rooted in \udta\meta\ilst\ which is referred to as 'Quicktime
atom format' |
|||||||||||||||||||||||||||||||||||
|
Metadata Item Atom |
00 |
00 |
00 |
35 |
A9 |
6E |
61 |
6D |
|||||||||||||||||||||||||||
|
size |
type |
|
|||||||||||||||||||||||||||||||||
|
|
|
|
|
©nam |
|
||||||||||||||||||||||||||||||||||
|
Value atom |
00 |
00 |
00 |
2D |
64 |
61 |
74 |
61 |
00 |
00 |
00 |
01 |
00 |
00 |
00 |
00 |
41 |
6E |
64 |
72 |
6F |
69 |
64 |
20 |
36 |
2E |
.. |
.. |
|
||||||||||
|
size |
type |
type indicator |
locale indicator |
type=1:
string |
|
||||||||||||||||||||||||||||||||||
|
|
|
|
|
data |
DF |
wknown types |
country |
language |
"Android
6.0.1 tags by Windows" |
|
|||||||||||||||||||||||||||||
User data text strings may use either Macintosh text encoding or Unicode text encoding. The format of the language code determines the text encoding format. Macintosh language codes are followed by Macintosh-encoded text. If the language code is specified using the ISO language codes listed in specification ISO 639-2/T, the text uses Unicode text encoding. When Unicode is used, the text is in UTF-8 unless it starts with a byte-order-mark (BOM, 0xFEFF), in which case the text is in UTF-16. Both the BOM and the UTF-16 text should be big-endian. Multiple versions of the same text may use different encoding schemes.
Now I ask myself: what happens if you put a ‘Quicktime format’ value atom in the root of a udta atom? For this I created a testfile using a hexeditor with that content. Most software like Ffprobe, Mediainfo, Exiftool and Online MP4 parser don’t read it correctly. As they should. By definition the atoms with the root \udta\ should be in the short format it seems.
3.3
Microsoft
Xtra atom
When an MP4 or MOV file is edited by Windows Properties in the ‘Details’ tab of (right mouse), an ‘Xtra’ atom is added or changed as \\moov\udta\Xtra. Besides this, several values are also added or changed in the \\moov\udta\meta atom.
Figure 1: Properties displayed in the Windows property editor by Windows.
Table 5: Properties displayed in the Windows property editor and the atoms where they are stored.
|
Section |
Property |
Xtra
key |
moov/udta/meta
key |
|
Description |
|||
|
Title |
- |
©nam |
|
|
Subtitle |
WM/SubTitle |
- |
|
|
Rating |
WM/SharedUserRating |
- |
|
|
Tags |
- |
- |
|
|
Comments |
- |
©cmt |
|
|
Media |
|||
|
Contributing
artists |
- |
©ART |
|
|
Year |
- |
©day |
|
|
Genre |
- |
©gen |
|
|
Origin |
|||
|
Directors |
WM/Director |
- |
|
|
Producers |
WM/Producer |
- |
|
|
Writers |
WM/Writer |
- |
|
|
Publisher |
WM/Publisher |
- |
|
|
Content
provider |
WM/ContentDistributor |
- |
|
|
Media
created |
cannot
be set |
- |
|
|
Encoded
by |
WM/EncodedBy |
- |
|
|
Author
URL |
WM/AuthorURL |
- |
|
|
Promotion
URL |
WM/PromotionURL |
- |
|
|
Copyright |
cannot
be set |
- |
|
|
Content |
|||
|
Parental
rating |
WM/ParentalRating |
- |
|
|
Parental
rating reason |
cannot
be set |
- |
|
|
Composers |
- |
©wrt |
|
|
Conductors |
WM/Conductor |
- |
|
|
Period |
WM/Period |
- |
|
|
Mood |
WM/Mood |
- |
|
|
Part
of set |
- |
disk |
|
|
Initial
key |
WM/InitialKey |
- |
|
|
Beats-per-minute |
- |
tmpo |
|
|
Protected |
cannot
be set |
- |
Information is not easy to find. The data can be stored in various types that are indicated by a type enumeration (like well-know types in the meta atom).
I cannot find this information as you would expect it on the
Microsoft website. Although many ‘keys’ that are used in the Xtra atom (e.g.
WM/Composer) are described in the WMF Attribute list
The actual enumeration used I found in Exiftool source code
Table 6: Type enumeration of Xtra values
|
Const Name |
Decimal |
Hexadecimal |
|
MP4_XTRA_BT_UNICODE |
8 |
$8 |
|
MP4_XTRA_BT_INT64 |
19 |
$13 |
|
MP4_XTRA_BT_FILETIME |
21 |
$15 |
|
MP4_XTRA_BT_GUID |
72 |
$48 |
Table 7: Example of an Xtra atom
|
Xtra atom |
00 |
00 |
03 |
14 |
58 |
74 |
72 |
61 |
||||||||||||||||||||||||||||
|
size |
type |
|||||||||||||||||||||||||||||||||||
|
788 |
Xtra |
|||||||||||||||||||||||||||||||||||
|
Key 1 |
00 |
00 |
00 |
2D |
00 |
00 |
00 |
13 |
57 |
4D |
2F |
53 |
68 |
61 |
72 |
65 |
64 |
55 |
73 |
65 |
72 |
52 |
61 |
74 |
69 |
6E |
67 |
00 |
00 |
00 |
01 |
|||||
|
key_size |
key_name_len |
key_name |
entry_count |
|||||||||||||||||||||||||||||||||
|
45 |
|
WM/SharedUserRating |
1 |
|||||||||||||||||||||||||||||||||
|
Value 1 |
00 |
00 |
00 |
0E |
00 |
13 |
19 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
||||||||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
|
|
|
|
19 |
|
|
|
|
|
|
|
|
||||||||||||||||||||||||
|
Key 2 |
00 |
00 |
00 |
2B |
00 |
00 |
00 |
0B |
57 |
4D |
2F |
53 |
75 |
62 |
54 |
69 |
74 |
6C |
65 |
00 |
00 |
00 |
01 |
|||||||||||||
|
key_size |
key_name_len |
key_name |
entry_count |
|||||||||||||||||||||||||||||||||
|
43 |
|
WM/SubTitle |
1 |
|||||||||||||||||||||||||||||||||
|
Value 1 |
00 |
00 |
00 |
14 |
00 |
08 |
4D |
00 |
79 |
00 |
53 |
00 |
75 |
00 |
62 |
00 |
74 |
00 |
00 |
00 |
||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
|
|
|
|
8 |
M |
. |
y |
. |
S |
. |
u |
. |
b |
. |
t |
. |
. |
. |
||||||||||||||||||
|
Key 3 |
00 |
00 |
00 |
3F |
00 |
00 |
00 |
0B |
57 |
4D |
2F |
43 |
61 |
74 |
65 |
67 |
6F |
72 |
79 |
00 |
00 |
00 |
02 |
|||||||||||||
|
key_size |
key_name_len |
key_name |
entry_count |
|||||||||||||||||||||||||||||||||
|
63 |
11 |
WM/Category |
2 |
|||||||||||||||||||||||||||||||||
|
Value 1 |
00 |
00 |
00 |
14 |
00 |
08 |
4D |
00 |
79 |
00 |
54 |
00 |
61 |
00 |
67 |
00 |
31 |
00 |
00 |
00 |
||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
20 |
8 |
M |
. |
y |
. |
T |
. |
a |
. |
g |
. |
1 |
. |
. |
. |
|||||||||||||||||||||
|
Value 2 |
00 |
00 |
00 |
14 |
00 |
08 |
4D |
00 |
79 |
00 |
54 |
00 |
61 |
00 |
67 |
00 |
32 |
00 |
00 |
00 |
||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
20 |
8 |
M |
. |
y |
. |
T |
. |
a |
. |
g |
. |
2 |
. |
. |
. |
|||||||||||||||||||||
|
Key 4 |
00 |
00 |
00 |
27 |
00 |
00 |
00 |
07 |
57 |
4D |
2F |
4D |
6F |
6F |
64 |
00 |
00 |
00 |
01 |
|||||||||||||||||
|
key_size |
key_name_len |
key_name |
entry_count |
|||||||||||||||||||||||||||||||||
|
|
|
WM/Mood |
1 |
|||||||||||||||||||||||||||||||||
|
Value 1 |
00 |
00 |
00 |
14 |
00 |
08 |
4D |
00 |
79 |
00 |
4D |
00 |
6F |
00 |
6F |
00 |
64 |
00 |
00 |
00 |
||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
|
8 |
M |
. |
y |
. |
M |
. |
o |
. |
o |
. |
d |
. |
. |
. |
|||||||||||||||||||||
3.4 EXIF tag data in general
The next section will be about the Nikon NCTG atom that contains data stored in an EXIF format. Therefore first this section, because this is more general and will also exist in other atoms.
EXIF data is stored using a tag and then the data, like this:
|
tag |
val_type |
count |
data |
In this section the tag is not discusssed, only how the value is stored and how to read it.
Like in the other containers of data, EXIF also works with a
type enumeration. I call these enumerators ‘val_type’ to keep consistency, but
they are specific to EXIF and also introduce the “rational”, wich is a fraction
of two 4-byte integers stored inside an 8-byte variable
The 2-byte ‘type’ is always followed by a 2-byte ‘count’. In structures described until now, the length of the total data is usually indicated by one value. In case EXIF data you have to find this by multiplying:
BytesToRead=(# bytes specified by ‘val_type’ enumerator) x (‘count’).
As regards the ‘tag’. EXIF data is stored using tags that are very specific for each case. So when inside an NCTG atom the tag 1 can mean the ‘Make of the camera’ while in a completely other case it can mean ‘depth under sea level’. The example shown in the next section will demonstrate how this works.
Table 8:
EXIF data type enumeration
|
Enumerator |
Format |
# bytes |
Comment |
|
1 |
unsigned byte |
1 |
|
|
2 |
ascii strings |
1 |
|
|
3 |
unsigned short |
2 |
|
|
4 |
unsigned long |
4 |
|
|
5 |
unsigned rational |
8 |
"rational" is fractional
value, first (u)int32 is numerator, 2nd (u)int32 is denominator |
|
6 |
signed byte |
1 |
|
|
7 |
undefined |
1 |
|
|
8 |
signed short |
2 |
|
|
9 |
signed long |
4 |
|
|
10 |
signed rational |
8 |
|
|
11 |
single float |
4 |
|
|
12 |
double float |
8 |
|
Xtra atom |
00 |
00 |
03 |
14 |
58 |
74 |
72 |
61 |
||||||||||||||||||||||||||||
|
size |
type |
|||||||||||||||||||||||||||||||||||
|
788 |
Xtra |
|||||||||||||||||||||||||||||||||||
|
Key 1 |
00 |
00 |
00 |
2D |
00 |
00 |
00 |
13 |
57 |
4D |
2F |
53 |
68 |
61 |
72 |
65 |
64 |
55 |
73 |
65 |
72 |
52 |
61 |
74 |
69 |
6E |
67 |
00 |
00 |
00 |
01 |
|||||
|
key_size |
key_name_len |
key_name |
entry_count |
|||||||||||||||||||||||||||||||||
|
45 |
|
WM/SharedUserRating |
1 |
|||||||||||||||||||||||||||||||||
|
Value 1 |
00 |
00 |
00 |
0E |
00 |
13 |
19 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
||||||||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
|
|
|
|
19 |
|
|
|
|
|
|
|
|
||||||||||||||||||||||||
|
Key 2 |
00 |
00 |
00 |
2B |
00 |
00 |
00 |
0B |
57 |
4D |
2F |
53 |
75 |
62 |
54 |
69 |
74 |
6C |
65 |
00 |
00 |
00 |
01 |
|||||||||||||
|
key_size |
key_name_len |
key_name |
entry_count |
|||||||||||||||||||||||||||||||||
|
43 |
|
WM/SubTitle |
1 |
|||||||||||||||||||||||||||||||||
|
Value 1 |
00 |
00 |
00 |
14 |
00 |
08 |
4D |
00 |
79 |
00 |
53 |
00 |
75 |
00 |
62 |
00 |
74 |
00 |
00 |
00 |
||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
|
|
|
|
8 |
M |
. |
y |
. |
S |
. |
u |
. |
b |
. |
t |
. |
. |
. |
||||||||||||||||||
|
Key 3 |
00 |
00 |
00 |
3F |
00 |
00 |
00 |
0B |
57 |
4D |
2F |
43 |
61 |
74 |
65 |
67 |
6F |
72 |
79 |
00 |
00 |
00 |
02 |
|||||||||||||
|
key_size |
key_name_len |
key_name |
entry_count |
|||||||||||||||||||||||||||||||||
|
63 |
11 |
WM/Category |
2 |
|||||||||||||||||||||||||||||||||
|
Value 1 |
00 |
00 |
00 |
14 |
00 |
08 |
4D |
00 |
79 |
00 |
54 |
00 |
61 |
00 |
67 |
00 |
31 |
00 |
00 |
00 |
||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
20 |
8 |
M |
. |
y |
. |
T |
. |
a |
. |
g |
. |
1 |
. |
. |
. |
|||||||||||||||||||||
|
Value 2 |
00 |
00 |
00 |
14 |
00 |
08 |
4D |
00 |
79 |
00 |
54 |
00 |
61 |
00 |
67 |
00 |
32 |
00 |
00 |
00 |
||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
20 |
8 |
M |
. |
y |
. |
T |
. |
a |
. |
g |
. |
2 |
. |
. |
. |
|||||||||||||||||||||
|
Key 4 |
00 |
00 |
00 |
27 |
00 |
00 |
00 |
07 |
57 |
4D |
2F |
4D |
6F |
6F |
64 |
00 |
00 |
00 |
01 |
|||||||||||||||||
|
key_size |
key_name_len |
key_name |
entry_count |
|||||||||||||||||||||||||||||||||
|
|
|
WM/Mood |
1 |
|||||||||||||||||||||||||||||||||
|
Value 1 |
00 |
00 |
00 |
14 |
00 |
08 |
4D |
00 |
79 |
00 |
4D |
00 |
6F |
00 |
6F |
00 |
64 |
00 |
00 |
00 |
||||||||||||||||
|
value_size |
val_type |
value |
||||||||||||||||||||||||||||||||||
|
|
8 |
M |
. |
y |
. |
M |
. |
o |
. |
o |
. |
d |
. |
. |
. |
|||||||||||||||||||||
3.5 Nikon NCTG atom
The Nikon tags are stored in an EXIF format (see 3.4 ). As described, for EXIF you need specific tables to find the meaning of each tag. They are just stored as numbers and can mean anything in every different case.
An example of EXIF data is the NCTG atom. This clearly demonstrates that you need a table to correlate what each tag means. In this case 1 means the make of the camera.
Table 9: Tag enumeration inside an NCTG atom (just parts; outtake of the total list)
|
1 |
Make |
|
2 |
Model |
|
3 |
Software |
|
17 |
CreateDate |
|
18 |
DateTimeOriginal |
|
19 |
FrameCount |
|
22 |
FrameRate |
|
25 |
TimeZone |
|
34 |
FrameWidth |
|
17859226 |
ExposureTime |
|
17859229 |
FNumber |
|
17860642 |
ExposureProgram |
A real-life example is shown in
Table 10. A simple example is Tag 1. The tag is 1. Lookup-value in Table 9 shows that it is the ‘Make’. The val_type is 2, lookup-value in Table 8 shows that it is a string. The count is 6, so 6 characters to read (including \0, so it is a null-terminated C type string). Strangely, Tag 2 is terminated by two zeros. In a similar way, as a string, the Createdate is stored (Tag 7). Notice that semicolons are use as separators.
An example of a ‘rational’ is shown in Tag 5. The tag enumerator is $17 (dec 23), which is not in tables I have found, but it looks like it is also the Framerate. The val_type is 5, a rational that is 8 bytes wide (Table 8). The four-byte numerator is 50000, the four-byte denominator is 1000, so the value is 50.
Table 10: Specific example of an NCTG atom (composed of different tags encountered)
|
NCTG atom |
00 |
00 |
xx |
xx |
4E |
43 |
54 |
47 |
||||||||||||||||||||||||
|
size |
type |
|||||||||||||||||||||||||||||||
|
|
NCTG |
|||||||||||||||||||||||||||||||
|
Tag 1 |
00 |
00 |
00 |
01 |
00 |
02 |
00 |
06 |
4E |
49 |
4B |
4F |
4E |
00 |
|||||||||||||||||||||
|
tag |
val_type |
count |
data |
||||||||||||||||||||||||||||||||
|
1=Make |
2 |
6 |
N |
I |
K |
O |
N |
. |
|||||||||||||||||||||||||||
|
Tag 2 |
00 |
00 |
00 |
02 |
00 |
02 |
00 |
0E |
43 |
4F |
4F |
4C |
50 |
49 |
58 |
20 |
50 |
39 |
30 |
30 |
00 |
00 |
|||||||||||||
|
tag |
val_type |
count |
data |
||||||||||||||||||||||||||||||||
|
2=model |
2 |
14 |
C |
O |
O |
L |
P |
I |
X |
|
P |
9 |
0 |
0 |
. |
. |
|||||||||||||||||||
|
Tag 3 |
00 |
00 |
00 |
03 |
00 |
02 |
00 |
16 |
43 |
4F |
4F |
4C |
50 |
49 |
58 |
20 |
50 |
39 |
30 |
30 |
20 |
56 |
65 |
72 |
2E |
31 |
2E |
34 |
31 |
00 |
|||||
|
tag |
val_type |
count |
data |
||||||||||||||||||||||||||||||||
|
3=softw. |
2 |
22 |
C |
O |
O |
L |
P |
I |
X |
|
P |
9 |
0 |
0 |
|
V |
e |
r |
. |
1 |
. |
4 |
1 |
. |
|||||||||||
|
Tag 4 |
00 |
00 |
00 |
13 |
00 |
04 |
00 |
02 |
00 |
00 |
00 |
4B |
00 |
00 |
00 |
00 |
|||||||||||||||||||
|
tag |
val_type |
count |
data |
||||||||||||||||||||||||||||||||
|
$13=framecount |
4 |
2 |
. |
. |
. |
K |
. |
. |
. |
. |
|||||||||||||||||||||||||
|
Tag 5 |
00 |
00 |
00 |
17 |
00 |
05 |
00 |
01 |
00 |
00 |
C3 |
50 |
00 |
00 |
03 |
E8 |
|||||||||||||||||||
|
tag |
val_type |
count |
data |
||||||||||||||||||||||||||||||||
|
$17=framerate? |
5 |
1 |
d uint32: 50000 |
d uint32:1000 |
|||||||||||||||||||||||||||||||
|
Tag 6 |
00 |
00 |
00 |
18 |
00 |
03 |
00 |
01 |
00 |
01 |
|||||||||||||||||||||||||
|
tag |
val_type |
count |
data |
||||||||||||||||||||||||||||||||
|
$18=unkn now |
3 |
1 |
1 |
||||||||||||||||||||||||||||||||
|
Tag 7 |
00 |
00 |
00 |
11 |
00 |
02 |
00 |
14 |
32 |
30 |
31 |
39 |
3A |
30 |
38 |
3A |
31 |
30 |
20 |
31 |
34 |
3A |
34 |
32 |
3A |
35 |
34 |
00 |
|||||||
|
tag |
val_type |
count |
data |
||||||||||||||||||||||||||||||||
|
17=Createdate |
2 |
20 |
2 |
0 |
1 |
9 |
: |
0 |
8 |
: |
1 |
0 |
|
1 |
4 |
: |
4 |
2 |
: |
5 |
4 |
. |
|||||||||||||
|
Metadata atom |
|||
|
Variable |
# Bytes |
Type |
Values |
|
Size |
4 |
uint32 |
variable |
|
Type |
4 |
uint32 |
'meta' |
|
Version |
1 |
|
1 |
|
Flags |
3 |
3 bytes |
|