[Digikam-users] Tags and metadata for photo and video

[Jean-François Rabasse]

Hello Cédric,
some comments as I see two different issues in your post.

On Thu, 17 May 2012, Cédric Macquat wrote:

> Hello,
> 
> I want to manage my photo collection and video collection with
> digikam. With digikam I tagged my photos and I want to begin with the
> video. My problem is the following: If I want to use another software
> to manage my photos and video in the future (perhaps one time another
> one will fit better to my needs, but for the moment digikam is
> perfect : -D) how can I make sure I don't have to retag everything ?
> When I will have much more photos and videos it won't be possible to
> do the work again.

The bad new is that (nothing but my own personal opinion) it doesn't
seem possible to expect setting up a tags strategy and keep it as is
along years or decades, and software changes.

Metadata world is a swampy and misty landscape. Some standards exist but
they mostly define data formats and labels, and are more unfocused on
data semantics and where to put what. A software development team may
have its own interpretation and another team may disagree and do
something different.
(Digikam itself does some interpretation in metadata handling, and not
everybody agrees.)

Also, software often needs some information not featured in standards
and will thus create its own namespaces for that.
Compatibility is then broken.
(Digikam does that. The tree structured tags system - a nice feature
indeed - is out of standards that propose only flat lists of keywords.
So, Digikam invents a special tag, xmp.digikam.tagslist, with special
syntax, Tag/Subtag/Subtag, that no other software will read.)

The good new (my personal opinion again) is that tagging and indexing
work should never be redone from scratch if you get prepared to do some
adaptation work. That work could be some home made scripts and command
line tools to extract all of your meta information, then feed under a
different way to suit the target management system.
(I happened to do that a few years ago, extracting structured indexes
from a SQL database, then rebuilding syntax compatible with
digikam.tagslist and feeding into images with exiftool. It took several
hours to build and check the tools but nothing was lost and it spared
hundreds of hours if reindexing from scratch would have to be done.)

The important thing is to tag and index fresh new stuff when it comes
under hand and trust for the future. Readable/writable information will
surely remain readable, and rewritable under a different form.


> ...
> But now I will tag my videos and with digikam it's not possible to
> create a xmp file for videos. I think the best way the retain the tag
> is to write in the metadata of the video, but how ? Or can I create an
> xmp sidecar for video with another software ? At the moment I'm
> looking at exiftool but until now I was not able to create an xmp
> sidecar for video with the same format as for the photos.

I have exactly the same problem, with non photos files. Videos yes,
and also, in my case, tracks logs GPX files I want to manage along with
images. The GPX format doesn't provide any metadata support, and Digikam
ignores that kind of file so, no XMP sidecar solution.

A possible solution is to create an image, JPEG format, for each of
those special files. For video files it's possible to use command line
tools as mencoder that allows extracting one video frame, the first one
or an offset one, and building a JPEG or PNG image. It works fine.
(For my GPX files, I use web services, e.g. GPS-visualizer that can create
a nice terrain map with the track overplotted in color.)

So, with Digikam, I don't tag the files but that « companion image ».
And when I do browse and search, I can find such an image and from name
and album name, I get the file. (Using a naming convention such as
xxxx.jpg is companion for xxxx.mpg, or xxxx.gpx, and lies into the same
folder.)

It's not that great, I admit, but it works well. If I happen some day to
know how to feed a video file with metadata, I'll probably move tags
information from the JPG to the MPG. As for today I don't know how, so I
live with thati, waiting for better days:-)

Maybe some other users will feed this thread with better ideas.

Regards,

Jean-François


PS: companion images, or placeholders, has recently been discussed on
this list, about an off-line data topic. Maybe for video files,
mostly very big files, indexing and managing a large video collection
could also require off-line data management along with that metadata
issue.
A companion image can merge both issues, for lack of anything better.