[libdvdcss-devel] cache: use libxdg-basedir and save cache into XDG-compliant location.

[Reimar Döffinger]

On 13 Mar 2013, at 01:45, Bernard Lang <blvlc at datcha.net> wrote:
> I understand from your reply that libdvdcss should encounter no CSS
> decoding problem if the drive is set on the region of the DVD.  If
> that is the case, then not being able to identify a key should be a
> rare event, and not such a major issue for most users ?

Yes, however not everyone may know/be able to set the region.
I think players on Linux usually neither report that nor is there a GUI for it I believe.

> * Reimar Döffinger <Reimar.Doeffinger at gmx.de>, le 28-02-13, a écrit:
>> If the video is long enough you should get decoding errors quite
>> reliably with the wrong keys.
> 
> I had at least one long title that disproves that. Decoding that title
> was strange in many respect. One key gave only the upper half of the
> screen.

Hard to know for sure without a sample, but it might be that the startcode for the second slice was corrupted.
It still seems likely the decoder discovered the file was broken, however e.g. FFmpeg until recently had the choice between either running error concealment or reporting an error, both was not possible. And the default behaviour was to run error concealment.

> This is why I raised the question of whether one can reliably check
> the correctness of a key.  And the answer seems to be no.

Unfortunately I think nowadays checking the key for correctness is the only thing that is difficult, since the key is "only" 48 bits and thus can be brute-forced (though it might take quite a few hours, so libdvdcss probably shouldn't use any dumb brute-forcing by default).