Include video from external IA collections in DDR file objects

[gjost]

See denshoproject/ddr-cmdln#245

ddr-densho-1024: IA Hundred Films project

We want to include this film (https://archive.org/details/cabemrc_000010) as a DDR object and display the video on ddrpublic. We want to use our regular media player on ddrpublic/ui/templates/ui/entities/detail-video.html. The

<video id="clip" class="embed-responsive embed-responsive-16by9 video-js vjs-big-play-centered vjs-fluid" controls preload="auto" width="560" height="384" poster="" data-setup="{}">
  <source src="{{ object.ia_meta.files.mp4.url }}" type="video/mp4">
    <p class="vjs-no-js">
      To view this video please enable JavaScript, and consider upgrading to a web browser that
      <a href="http://videojs.com/html5-video-support/" target="_blank">supports HTML5 video</a>
    </p>
</video>

what's difference in IA code betw VH segment (e.g. ddr-densho-1000-1-1-mezzanine-0762419626) and just an AV object (e.g. ddr-densho-354-2125, https://ddr.densho.org/ddr-densho-1020-13/?format=av)?
in order to display the video link, template uses object.ia_meta..mp4
where does that come from?
can we insert an IA video from some other organization into a DDR object?

VH: https://ddr.densho.org/api/0.2/ddr-densho-1000-1-1-mezzanine-0762419626/

• has external_urls
  https://ddr.densho.org/api/0.2/ddr-densho-354-2125/

Examples from Sara
https://archive.org/details/cabemrc_000010
https://ddr.densho.org/ddr-densho-1020-13/?format=av
https://archive.org/details/ajahp-VT_208

[gjost]

Initial work as of commit 5e66608 on branch 245-external-ia-media. Added alternateid templatetag to handle the more complex logic for displaying the alternate ID, possibly with links.

[gjost]

Previous work published a URL using the server and dir from the IA metadata. This worked, but the resulting URL refers to internal IA servers by subdomain, and looks like it may not be stable.

In the current iteration (ddrcmdln 8fe9b82, ddrpublic e5d9a10), ddrcmdln publishes only the ia_external_id to Entities' ia_meta. When ddrpublic sees an entity with an ia_external_id, it asks IA for the metadata (this request is cached) and assembles a URL for the mp4 which it inserts into the ia_meta. The existing detail-video.html template is used as-is.

[gjost]

Completed in 3709a2f, merged into master in d933005.