[packman] dcadec and FFmpeg

[Martin Herkt]

Someone has written an LGPLv2-licensed DTS decoder with support for HD 
extensions, and two days ago support for it was added to FFmpeg (previously, 
FFmpeg was unable to decode DTS-HD Master Audio in a lossless way). This is 
likely to be included with one of the upcoming FFmpeg releases, so I figured 
it’d be a good idea to let you know in advance.

The project can be found here: https://github.com/foo86/dcadec

For now, I’ve contributed some rudimentary Makefile changes upstream that 
should make packaging easy enough, but there may be some remaining issues.

Support in FFmpeg is enabled with the --enable-libdcadec compile-time switch.