How do I open an .aca file?

Can I open my .aca files

Audio and Video Development3

You refer to the content of aca files using specially crafted URIs in markup/script e.g.

file:///hddvddisc/ADV_OBJ/myfile.aca/foo.jpg

i.e. treat the aca file as if it were a directory.

So are you saying I can create the uri in windows explorer (to that jpg) and view it I tried that (png file actually) and it did not work.

"Windows cannot find <path>"

Sorry, I misunderstood you. Windows has no concept of .aca files so cannot decode them.

I thought you were wanting to consume them from HD DVD code.

Is the ECMA script obfuscated when written to archive

The CreateACA tool shipped with iHDSim does not do any obfuscation; an ACA is simply an archive file like a ZIP file (but without the compression). If you opened it up in a binary editor, you would see all the raw text after some header information. If you have the HD DVD spec, it would be fairly trivial to write a de-ACA program.

If you have an AACS-protected disc, then you have the option of encrypting the script code (both inside and outside of ACAs).

I wanted to check out some of the javascript on the Serenity and Million Dollar Baby HD-DVDs, but when I open the aca in a hex editor, I can read the xml but not the javascript.

So I assume that obfuscation is intentional

Yes, in that case they have used a different tool and have AACS-protected their script. The XML is only protected against tampering (modification), but the script is also protected against viewing (so you don't copy their code).