With the current version, if a trailer does not exist in the download list, but does exist on the hard drive, it is still downloaded again, though this does not make any sense.
So if a local file exists with the same file size as on the server, simply skip downloading and add the filename to the download list.
(On a side note, if it's easy to make support for resuming incomplete downloads, it would be a nice thing, but this is really not so important, as downloading a trailer goes quite quickly with today's broadbands.)
With the current version, if a trailer does not exist in the download list, but does exist on the hard drive, it is still downloaded again, though this does not make any sense.
So if a local file exists with the same file size as on the server, simply skip downloading and add the filename to the download list.
(On a side note, if it's easy to make support for resuming incomplete downloads, it would be a nice thing, but this is really not so important, as downloading a trailer goes quite quickly with today's broadbands.)