There was recently a discussion about this setting on the libreplanet-discuss list. ​https://lists.gnu.org/archive/html/libreplanet-discuss/2021-05/msg00013.html

I see there was an issue about it 9 years ago. https://issues.mediagoblin.org/ticket/375#no2

The issue suggests using preload="metadata" instead.

These are the two commands I used to find it:

git clone --branch v0.11.0 --depth 1 ​https://git.savannah.gnu.org/git/mediagoblin.git grep -R 'preload="auto"' mediagoblin/

mediagoblin/mediagoblin/plugins/archivalook/templates/archivalook/feature_displays/video_primary.html: preload="auto" class="video-js vjs-default-skin"> mediagoblin/mediagoblin/plugins/archivalook/templates/archivalook/feature_displays/video_secondary.html: preload="auto" class="video-js vjs-default-skin"> mediagoblin/mediagoblin/templates/mediagoblin/media_displays/video.html: preload="auto" class="video-js vjs-default-skin" id="video_1">

It seems to me that set_models_as_attributes() refers to some sqlalchemy internals which simply don't exist anymore in sqlalchemy 1.4.0b1, causing my initial/fresh database migration to fail.

So, my new deployment of MediaGoblin explicitly pins sqlalchemy to a version that I know works for sure from a previous deployment (1.3.20) and just like that, the initial database migration works perfectly again.

For whatever it's worth, here's the patch I applied in my copy of MediaGoblin: ​https://github.com/dressupgeekout/mediagoblin-dressupgeekout/commit/b85894dddc2d304f1aff05afce99d5dfa44b1b09

​https://mediagoblin.readthedocs.io/en/stable/siteadmin/media-types.html (docs/source/siteadmin/media-types.rst) says to install python3-pyexiv2, but I do not see python3-pyexiv2 as a Debian package.

There is a python-pyexiv2 in the Debian repos and pyexiv2 in pypi. Looks like python3-pyexiv2 should be python-pyexiv2. If that is correct, this command should fix it:

sed -i 's/python3-pyexiv2/python-pyexiv2/' docs/source/siteadmin/media-types.rst