Where to add app screenshots?

[agron2017]

I would like to add a few screenshots and maybe even some videos to a few apps like audacity, cantata, vivaldi but there is no information as where to find the database, or xml files for such entries.
I initially asked on Manjaro Linux forum but the directed me here to appstream.

[JakobDev]

The AppStream files are ususally managed by the Applications itself e.g. for Audycity you can find it here. They are ususlly in the main source Repo of the App.

On Flathub, it can happen that the App itself has no Appstream file but Flathub requires Appstream file. In that case, it is in the Flathub Repo e.g. Google Chrome.

If a App on the normal Repos of a Distro has no Appstream file, appstreamcli will usually generate one from the .desktop file of the App. This is missing some important in finformation e.g. Screenshots, but it's better than nothing.

There is no central place to find them. You have to look for each Application.

[ximion]

You indeed need to add this data to the upstream projects. Each project is managing their own data and is in full control of that, AppStream just defines how that data should look like.

If you are just interested in a list of metadata and screenshots, Flathub as well as distributions such as Debian generate that data from the upstream-provided files: https://appstream.debian.org/sid/main/metainfo/index.html