Understanding Metadata Sources

Many video cameras can store the recording date and time, exposure settings and geographical coordinates while they are recording video. This information is termed "metadata" and it is stored in special areas of the video data that is usually inaccessible or unreadable. If you take a file that was created by a video camera and play it in DVMP Pro, it is able to read this information and display it in a window pane beneath the video as it plays. So you can see how the date, time, exposure details and geographical coordinates change as the playback progresses. Each of the items displayed is described in detail in the Metadata Items chapter.

 

The amount of this metadata that is stored can vary a lot between camera models - some may only store date and time and nothing else; some may store aperture and shutter speed but not zoom details etc.

 

It is important to understand that some models may not store any metadata at all - in this case it is impossible to see the date and time that the recording was made, or the exposure settings that were used. Fortunately most common camcorder recording formats such as AVCHD do record at least the date and time, and often exposure details too.

 

Nevertheless, it is impossible to say for sure what metadata is stored by any particular model of video camera. The only way you can be sure is to try playing one of the camcorder files in DVMP Pro and see what information is displayed - missing items will be displayed as a series of hyphens "-----" which indicates that your camera does not store that particular item of metadata. This is why we require all prospective customers to try out the DEMO version of DVMP Pro with files from their own video cameras - so they can check whether their video camera stores the required items of metadata before they decide to purchase a license for the FULL version.

 

Camcorders can store this metadata information in several different ways. Some camcorders store the information within the video stream; some store it in a file header; and some store it in a completely separate file that accompanies the video file (sometimes referred to as a "sidecar" or "partner" file). These different storage places are termed "Metadata Sources".

 

Here is a list of the Metadata Sources that are used by various video camera types:

 

Embedded metadata - the metadata is stored within the video stream and is continuously varying as the file is played or burned-in
THM file - the metadata is stored in a separate file with the same name as the video file except that it has a .THM file name extension
MOI file - the metadata is stored in a separate file with the same name as the video file except that it has a .MOI file name extension
MPL file - the metadata is stored in a separate file with the file name extension .MPL
File header - the metadata is stored in the video file's basic or advanced headers. It is stored only once, so it does not vary as the file is played or burned-in
Filesystem "Date Created" - only the recording date and time is stored. It is stored as the "Date Created" Windows file property which you can also see as a column in File Explorer or Windows Explorer.
Filesystem "Date Modified" - only the recording date and time is stored. It is stored as the "Date Modified" Windows file property which you can also see as a column in File Explorer or Windows Explorer

 

Please note that Embedded metadata stores exposure and geographical items as continuously varying values so that you can see them change as the file is played (or burned-in). All of the other Metadata Sources only store single non-varying items that usually correspond to the instant that the camera began recording. However, the recording date and time items are continuously varying for all Metadata Sources.

 

Depending on the camera's video file type, some of these Metadata Sources are more likely to be used by the camera than others, so DVMP Pro will usually be able to choose the correct Metadata Source itself without you having to worry about it. However, you can also override this and choose a specific Metadata Source yourself if you feel that you need to.

 

It's very important to realize that some Metadata Sources are more reliable than others. Embedded metadata is the most reliable because the metadata is stored inside the video file and the file specifications usually define exactly how each item of metadata must be stored by the camera. Embedded metadata also tends to contain more items of information, and the items usually change throughout the file - these both mean that more information is usually available from Embedded metadata.

 

Metadata Sources where the metadata is stored in a separate sidecar file (THM, MOI and MPL) are less reliable because the sidecar file may become separated from the video file - for example it may get accidentally deleted, renamed or overwritten by you or by other software. If DVMP Pro can't find the sidecar file then it will be unable to display or burn-in any metadata items.

 

File header is reliable because the metadata is stored inside the video file. However, the specification for storing metadata in basic file headers is less strict and therefore tends to be less reliable than Embedded metadata. For example, some cameras may store the time in local time while others store it in Greenwich Mean Time (GMT or UTC). Fortunately, some camera models store an additional Advanced file header which contains date, time and other information that is much more reliable than the basic file header. If an Advanced file header is present in the video file, DVMP Pro will use it in preference to the basic file header.

 

Filesystem "Date Created" and Filesystem "Date Modified" are by far the least reliable and should be avoided if at all possible. These are actually the Windows file properties that you can see in the "Date Created" and "Date Modified" columns of File Explorer or Windows Explorer. When a camcorder creates a video file on its media, the camera's filesystem will usually set the file's Date Created and Date Modified properties to the date and time when the recording started. However these file properties are quite fragile and may be changed by other software without you noticing - in some cases just copying files can result in one of these file properties being changed. DVMP Pro can not know if these properties have been changed; it will simply show you the date and time of the properties as they are when the file is played or burned-in. However, some camcorders may not store metadata in any other way, so you may feel that you have little choice but to use Filesystem "Date Created" or Filesystem "Date Modified". Just be warned that this may give you incorrect results, and be sure to test your workflow thoroughly so that you may have greater confidence that no external factors are changing the date and time. But try to avoid using these two Metadata Sources if you can.

 

Regardless of the Metadata Source, if the recording date and time stored by the camera is not accurate, then you can correct it by using the Adjust Date and Time by setting in Tools > Options > Metadata Sources.

 

When you play a file in DVMP Pro, the chosen Metadata Source is displayed as a 3-character label to the right of the recording time. The metadata items are also displayed in red where the values are stored within the video file; in yellow where the values are stored in a separate sidecar file; and in grey for the less-reliable Filesystem "Date Created" and Filesystem "Date Modified".

 

Label

Metadata Source

Color

EMB

Embedded metadata

 Red 

HDR

Basic file header

 Red 

HDA

Advanced file header

 Red 

THM

THM file

 Yellow 

MOI

MOI file

 Yellow  

MPL

MPL file

 Yellow 

DTC

Filesystem "Date Created"

 Grey 

DTM

Filesystem "Date Modified"

 Grey 

 

Each supported file type has a list of Metadata Sources that you can choose from in Tools > Options > Metadata Sources. Some contain a prioritized list of Metadata Sources separated by a ">" which DVMP Pro will try in turn. The prioritized list is the recommended setting because it allows DVMP Pro to decide the best Metadata Source automatically. Always choose the setting marked "recommended" unless you are sure you want another Metadata Source to be used instead.

 

The Metadata Sources for each supported file type are shown below.

 

DV AVI & Raw DV files

 

Embedded metadata (recommended)
Filesystem "Date Created"
Filesystem "Date Modified"

 

DV MOV files

 

Embedded metadata (recommended)
File header
Filesystem "Date Created"
Filesystem "Date Modified"

 

HDV M2T files

 

Embedded metadata (recommended)
Filesystem "Date Created"
Filesystem "Date Modified"

 

AVCHD MTS/M2TS files

 

Embedded metadata > MPL file (recommended)
Embedded metadata
MPL file
Filesystem "Date Created"
Filesystem "Date Modified"

 

MPEG-2 Program Stream files (MPG, VOB, MOD)

 

Embedded metadata > THM file > MOI file (recommended)
Embedded metadata
THM file
MOI file
Filesystem "Date Created"
Filesystem "Date Modified"

 

MOV & MP4 files

 

THM file > File header (recommended)
THM file
File header
Filesystem "Date Created"
Filesystem "Date Modified"

 

 

Each Metadata Source is described in greater detail below.

 

For all Metadata Sources, if the recording date and time stored by the camera is not accurate, then you can correct it by using the Adjust Date and Time by setting in Tools > Options > Metadata Sources.

 

Embedded Metadata

 

The metadata items are stored as continuously changing values while the camera is recording. So for example if the camera's aperture changes while a recording is being made then you will be able to see this happen in "real-time" when you play the file in DVMP Pro. If you are using the Burn-in tool then you will also see the the values change in the burned-in file.

 

For files which have Embedded Metadata this is the most reliable Metadata Source because the metadata values are stored within the video file and so can not become separated from it. Embedded Metadata also tends to contain more metadata items than other Metadata Sources. Always prefer Embedded Metadata where available.

 

File Header

 

The metadata items are stored as single values in the video file's basic header or advanced header. The values usually apply to the instant that the camera created the file. Like Embedded Metadata the values are stored within the video file and so can not become separated from it - in this sense it is reliable. However the specifications for storage of metadata in basic file headers is much looser so it is less reliable than Embedded Metadata.

 

For example, MOV and MP4 files are created by many types of video recording devices, some of which may not store the date and time reliably in the basic file header, even if the device's own clock had been set correctly when the recording was made. Some recording devices may store the time without any daylight-time adjustment. Some may store the time as Greenwich Mean Time (GMT) rather than the local time, so depending on where on earth the footage was shot the time may appear to be several hours different to the local time when the recording was made. Worse still, some budget devices even store a single fixed date and time for every file that it records, so for example all files may seem to have been recorded on 1st January 2004 (or any other arbitrary date and time). And of course some devices may not store any date and time at all.

 

Fortunately, some devices also store an Advanced header that contains date, time and other information that is much more reliable than the basic header. If the video file contains an advanced header then DVMP Pro will use that instead of the basic header. When playing the video file, the presence of an advanced header is indicated by the HDA label - if there is only a basic header the label will be HDR.

 

If you have video files that only have a basic header, you need to take extra care. If you have access to the camcorder that recorded the files, then you can simply make a test recording at a known time of day, and then play the recorded file in DVMP Pro and compare the displayed date/time with your known time to see if they are different, and by how much. If the difference was consistent, you could then use the Adjust Date and Time by setting in Tools > Options > Metadata Sources to effectively "remove" the difference. But if you do not have access to the camcorder that recorded the files, then there is no way of knowing whether the date and time stored by the camcorder in the basic header was in local time, daylight saving time, GMT, etc. In that case you should treat the displayed date and time as being unreliable, and find some other independent proof of the true date and time when the files were recorded.

 

THM File

 

THM files are created by some cameras that record to MPEG-2 Program Stream, MOV or MP4 files. A THM file is created for each video file and it has the same name except that it has the file name extension .THM - so a video file with the name MOV003.MPG would have a partner MOV003.THM file in the same folder on the camera media.

 

The THM file contains the metadata for its partner video file. The metadata items are stored as single values in the THM files and the values usually apply to.the instant that the camera started recording the video file.

 

Because the metadata is stored in a separate file you must ensure that whenever you copy or move the video files you also copy/move the THM files into the same folder. If DVMP Pro can not find the corresponding THM file in the same folder as the video file then it will be unable to display or burn-in the metadata values.

 

MOI File

 

MOI files are only created by cameras that record to MOD video files.

 

A MOI file is created for each video file and it has the same name except that it has the file name extension .MOI - so a video file with the name MOV003.MOD would have a partner MOV003.MOI file in the same folder on the camera media.

 

The MOI file contains the metadata for its partner MOD video file. The metadata items are stored as single values in the MOI files and the values usually apply to.the instant that the camera started recording the video file.

 

Because the metadata is stored in a separate file you must ensure that whenever you copy or move the video files you also copy/move the MOI files into the same folder. If DVMP Pro can not find the corresponding MOI file in the same folder as the MOD video file then it will be unable to display or burn-in the metadata values.

 

MPL File

 

MPL files are created by some AVCHD video cameras. Usually Embedded metadata is a better choice of Metadata Source, but a small minority of AVCHD cameras do not store any Embedded Metadata at all.

 

In the AVCHD format, the MTS video files are stored in a folder called STREAM on the camera's media. The MPL files are stored in a sister folder called PLAYLIST.

 

Unlike the THM and MOI files, there is not a one-to-one correspondence between MTS video files and MPL files. An MPL file may contain the metadata for several MTS video files.

 

When you open an MTS file in DVMP Pro and the MPL metadata source is chosen, it searches for an MPL file that contains the metadata for that MTS file. It only searches for MPL files in a sister folder called PLAYLIST, or in the same folder as the MTS file. Consequently, if you were to copy the MTS files to a folder on your computer, you could copy the MPL files into a sister PLAYLIST folder; but if you find it more convenient to copy them into the same folder as the MTS files then DVMP Pro will also find them there.

 

See Also:

Playing Video Files