More interesting metadata would be retrieval of the time signature (rows per beat / rows per measure) - either the current time signature (least versatile), retrieve time signature by pattern ID, or some function to check if a given row is the start of beat or measure (most versatile, also supports more than one time signature per pattern, in case we ever need that).

This can be used for syncing or pattern drawing purposes.

It would probably make sense to have separate metadata APIs for numeric metadata, such as the aforementioned rows per beat stuff (unless we want to put that in its own API function, of course). For samples and instruments, this would also make sense. It would certainly be better than just having string-based metadata APIs where the user basically has to convert the string back to a float (or int) on every invocation.

I would like to get all the info from a sample/instrument. Name, size, loop start, sample data etc. Just return a vector with with the sample/class/structs. Take a look how libxmp did it.