Hi Peter,
In our institution, we take the approach of implementing PREMIS based
on our analysis of the file format from practical point of view. For
every file we archive, a file object is used to store the general file
metadata such as format, checksum, size, etc. Format specific
metadata is placed inside the objectCharacteristic of either file or
bitstream object, depending on the file format.
For WAVE, the audio metadata is placed inside the objectCharacteristic
of the file object. Our understanding is although the WAVE format
specification doesn't explicitly prohibit putting multiple audio
tracks inside a WAVE file, in practice, we only see an audio stream
inside a WAVE file so that's the most practical way of implementing
PREMIS from our perspective. An audio stream is defined as an audio
data stream with all the audio metadata. So even there are various
metadata chucks for the audio data stream inside WAVE, it's all
considered as one audio stream. For broadcast wave, though it
contains additional chucks, they are considered as metadata chunk thus
is not considered as individual audio stream.
For multimedia formats like AVI and MOV, each audio and video streams
will be considered as PREMIS bitstreams because we want to have the
ability to characterize each video and audio separately. Same
principle goes to TIFF since a TIFF file can contain more than one
image and each image can have different characteristic that we want to
capture. So for a TIFF with just one image, the image metadata will
still be put into the object characteristic of a PREMIS bitstream.
JPEG image, on the other hand, is put into file object, because a JPEG
file contain only one JPEG image. For PDF, we put document specific
metadata in the file level but the metadata for all the bitstreams
like images inside the PDF are considered as bitstream objects.
Attached is am example of our PREMIS document for a WAVE file. We
also have a web service on our web site where you can submit a file
and generate a PREMIS document for it. You may access the web service
at description.fcla.edu.
Thank you,
-Carol Chou
Florida Center for Library Automation
2011/11/16 Peter McKinney <[log in to unmask]>:
> Dear Listmembers,
>
>
>
> I wonder if any of you might be able to offer advice. I’m getting confused
> with information I should be writing to the file level and which to the
> bitstream level.
>
>
>
> We collect a lot of wave audio files. They are brought into our system and
> run through format ID and metadata extraction (among other things). My
> understanding of PREMIS is that the audio chunk of the wave file should be
> treated as a bitstream. Does this mean that all the technical metadata
> extracted for that wave file should actually be written to the bitstream
> level, as it mostly relates to the audio chunk?
>
>
>
> Likewise, how do I deal with the other chunks? If I’m dealing with, say, a
> Broadcast Wave, are all the chunks bitstream? Meaning, what do I do if I
> want to extract the metadata from them? Do I write them to a new bitstream
> object?
>
>
>
> I guess what I’m trying to get at here is what defines whether you have a
> bitstream or not? Why are the images in a multi-page tiff bitstreams, but
> the single image in a tiff is not (or is it?)? What if it is a tiff with one
> image and exif metadata?
>
>
>
> There’s something in this also around tools and systems capabilities as
> well. The tools we use don’t view files through a PREMIS lens. In addition,
> the systems and tools that we use do not offer unlimited flexibility and it
> is conceivable that we will wind up writing conceptually different things to
> the same PREMIS level as a result. The audio chunk of a Wave file would be
> described as a bitstream if the file is ingested on its own but the entire
> file will be considered a bitstream if it is encapsulated in a WARC or
> Baggit file.
>
>
>
> I’d be really grateful for any thoughts on this topic, especially if those
> thoughts contain examples!
>
>
>
> Thanks,
>
> Pete
>
>
>
>
>
> Peter McKinney
>
> Digital Preservation Policy Analyst
>
> Preservation Research and Consultancy
>
> National Library of New Zealand Te Puna Mātauranga o Aotearoa
> The Department of Internal Affairs Te Tari Taiwhenua
> PO Box 12-340, Wellington 6144
> 77 Thorndon Quay, Thorndon, Wellington 6011
>
> Direct Dial: +64 (4) 462 3931
>
> www.dia.govt.nz
>
>
>
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