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[Michi Henning <michi.henning@xxxxxxxxxxxxx>]

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.)

-- 
You received this bug notification because you are a member of Ubuntu
Touch seeded packages, which is subscribed to thumbnailer in Ubuntu.
https://bugs.launchpad.net/bugs/1532732

Title:
  Caching for arbitrary images on the web/remote hosts

Status in thumbnailer package in Ubuntu:
  New

Bug description:
  I frequently hit the use case that I query some host (might be in my
  local network, might be on the internet) for a list of things. The
  result set comes with images so I present a scrollable list of all
  those things to the user.

  Problem now is that with the images being fetched, the list scrolling
  is somewhat stuttery and also presents empty images at first which
  then are only filled with content a bit later. Scrolling the list back
  up, same thing again happens as the in-QML caches we have are based on
  RAM and with that can't hold tons of images. They are discarded and
  scrolling the list back up causes them to be reloaded.

  
  It would be great if the Thumbnailer could take care of this and fetch and cache them for the developer.

  One point to think about would be timeouts. Some use cases will always
  present the same image again. For example in kodimote I fetch the
  music artwork given by kodi. The artwork won't ever change, so the
  cache can be persistent. At the same time, fetching things from an
  online server *might* change over time. Ideally this would be
  configurable so that the developer can specify some cache time out for
  entries.

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