Easy: ship source code and the whole compiler toolchain, also in source form, with bootstrapping instructions for a generic machine that future archaeologists will trivially port to whatever architecture is in vogue in year 32768 !

Joke aside, this question is close to the file format obsolescence problem in long term digital preservation: the longer the term, the closer to bootstrapping the answer is.

In the shorter term, detailed metadata, widely used containers and choice of codecs that have well-known open source implementations is a good start.