[MPlayer-dev-eng] aes & bluray

[Reimar Döffinger]

On Fri, Sep 11, 2009 at 11:55:13AM +0200, Reimar Döffinger wrote:
> On Fri, Sep 11, 2009 at 11:42:40AM +0200, Nico Sabbi wrote:
> > Il venerdì 11 settembre 2009 11:32:06 Reimar Döffinger ha scritto:
> > > Either way I admit I would simply like to have libavformat _also_
> > > support decrypting (because lavf already has some other decryption
> > > stuff, so this could be some kind of common way to handle all kinds
> > > of encryption, MXF, ASF, AACS etc.), and I would also like it if
> > > the scrambling control checks would be re-added in the demuxers in 
> > > a well-tested way so that people trying to play encrypted files
> > > (e.g. when people do a simple file copy from a DVD) at least get a
> > > proper warning instead of just strangely broken playback.
> > > Overall I just have the feeling that at the demuxer layer it would
> > > solve a whole bunch of problems more.
> > 
> > well, in this case we need a .decrypter member to inizialize at 
> > demux_open() according to the stream type.
> > I don't particularly like the idea, but...
> 
> Do you _know_ that this is needed or are you just guessing? As said, I
> have not found much documentation, particularly about CSS at the demuxer
> level so I don't know if the demuxer really needs to know the stream
> type. I do know that DVB and HD-DVD can be distinguished with nothing
> more than the value of PES_scrambling_control.

And CSS and AACS can be distinguished by key size: CSS is 40 bits and
AACS is one or more 128 bit keys.
Now, I admit that this _might_ still be ugly, but I do believe that this
is possible without breaking stream/demuxer layering.
I also admit that there might be some issue with CSS due to title
and associated key changes, as I understand it that is no issue with
AACS since the stream contains the info which key out of a list of keys
to use.
Of course to some level this discussion is a bit pointless with probably
nobody volunteering to implement this at the demuxer layer...