Setting was previously preload="auto". While preload="auto" *does not* cause a
full upfront download on Firefox, Abrowser, IceCat or Chromium, a user reported
on the LibrePlanet mailing list that it was causing a full download on their
browser. The specifications leave it up to the browser do decide whether to
download, but it makes sense to do what we can to avoid surprising people on low
bandwidth/quota internet connections.
https://html.spec.whatwg.org/multipage/media.html#attr-media-preload
Further, media.libreplanet.org (one of MediaGoblin's biggest users) has
implement this change locally, so it makes sense for us to stay in sync.
Signed-off-by: Ben Sturmfels <ben@sturm.com.au>
bc2990c279