Comment 1 for bug 1532732

Doing this would not be hard. The underlying persistent-cache-cpp thingy already handles TTL eviction. The time to live can be set on a per-thumbnail basis. So, you can just ask for a thumbnail and provide an expiry time, and the thumbnail will automatically be re-fetched once it expires. Or you can leave the timeout off, and then the thumbnail will hang around the cache using LRU until it isn't accessed often enough to drop out of the cache completely (at which point it would be automatically re-fetched as needed).

The key you would provide for this would be the URL to the image file.

If you want to thumbnail images that you have extracted yourself (where the images do not have URL that directly points at them), you can do that today. Doing so requires you to write them into the file system and to then ask for a thumbnail with a URL that points at the local file. (That's how photos are being thumbnail, for example.) The cost of this approach is increased disk space because the thumbnailer absolutely will not provide a thumbnail for a local image unless you can prove that you are entitled to actually read that image. In practice, this means that, as soon as the original image from which a thumbnail was generated is deleted, the thumbnailer will no longer hand out a thumbnail for that image.

All this would work for any file type that is currently supported. (Basically all image file formats in the known universe, plus most audio and video formats, provided the necessary gstreamer codecs are installed.)