use of umid's - please help
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Author:  Tommy [ Fri Jan 11, 2008 10:10 pm ]
Post subject:  use of umid's - please help


I need clarification please, regarding the use of
UMID's in an MXF file, specifically where they need to match.

I'm not clear whether UMID's need to match sometimes within an
mxf file.
UMID's are used in many places within an mxf file, including:

in the header metadata -
> in essence container data, linked package umid (p. 65 S377M)
> in each package, a package umid (p. 66 377M)
> in sourceclip subset, a SourcePackageId (p. 70, 72)

Then, in each edit unit's package metadata, there is a UMID
metadata field ( type = 0x83, SMPTE 331M p. 10)

In our mxf file, we plan to have a material package and a file
package in the header metadata, and then mpeg2 video along
with audio and timecode in the essence containers.

Can you please tell me where the UMID's need to be the same
in an mxf file, and where unique UMID's are required?

And then can UMID's (and UUID's) be duplicated in other files,
or do they need to be unique from 1 file to the next?

Thanks a lot, Tommy Schell

Author:  Matt Beard [ Sun Jan 13, 2008 10:35 am ]
Post subject: 

When you examine the metadata of an MXF file you will see that although each file package describes the properties of an essence stream (or group of essence streams) in detail, it does not say where this essence is stored.

To find out where the described essence is stored you locate it using the UMID from that package.

If the essence is external to the MXF file then some form of MAM lookup will need to be performed using this UMID.

If the essence is internal to the MXF file the lookup is done using the EssenceContainerData sets in the ContentStorage set. This links each BodySID in the file with a UMID, and hence with the package that describes the essence.

So, every UMID in an EssenceContainerData set in an MXF file must match the UMID of a top-level file package in that same file.

The UMID in a material package is the identifier of the output of this file - basically it is the identifier for the whole of the file as described. This UMID would then be registered in your MAM to give a link to this file.

UMIDs should never be reused in different MXF files unless they are referring to exactly the same essence (for example if the file is an exact copy or you are deliberately referring to essence in one MXF file from another).

UUIDs used for InstanceIDs can be repeated in different MXF files as thier scope is limited to a single instance of header metadata. However, UMIDs always have global scope.

Author:  Tommy [ Mon Jan 14, 2008 9:47 pm ]
Post subject:  Re: use of UMID's in MXF files

Thanks for the reply.

So for clarification, we are generating MXF files where the essence is
internal to the file, basically following the model used by Sony as
outlined in RDD 9-2006 (MPEG2, operational pattern OP1A).

I examined a Sony XDCAM MXF file closely, and noticed that:

> As you suggested, the file package UMID matched the EssenceContainerData linked package UMID in the header metadata.
Additionally, this value was matched in the SourceClip subset (SourcePackageId, local tag 1101, p.70, 72 S377M) for both
picture and sound, within the material package.
Does this sound correct?

> The material package UMID (32 bytes) was matched in the package metadata subset's UMID field within each of the edit units (the essence)
in the file.
However, the values in the package metadata were expanded out
to 64 byte values, and the 32 byte extension appeared to change
from 1 edit unit to the next, with the 1st 32 bytes not changing.

Is a 64 byte UMID value necessary, or is a 32 byte value matching the
material package UMID sufficient within the edit units?

Thanks, Tommy

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