Avro files have a header which has metadata including the schema as well as things like compression codec (supports deflate and snappy) and all of the implementations that I have used (java and python bindings mostly) just does this in the background.

Another fun thing is that avro supports union types, so to make things nullable you just union[null, double] or whatever.

But one of the best things about avro (and parquet for that matter) is that it is well supported by the hadoop ecosystem