op_fopen() and op_freopen() declare these arguments as non-NULL, so when building with mingw, the compiler reasonably complains when we check to see if they're NULL. We could remove the OP_ARG_NONNULL tags, but the behavior of _wopen/_wfreopen appears to be to crash on NULL for either parameter. On Linux, the behavior appears to be to handle a NULL path (fopen returns NULL with errno set to EFAULT, and freopen returns the passed FILE * with errno set to EFAULT), but crash on a NULL mode. Keeping the OP_ARG_NONNULL tags promises that passing NULL results in undefined behavior, which is at least consistent with the behavior being different on different platforms. It's also consistent with the ABI promises of previous releases, which compilers linking against libopusfile might have taken advantage of.
The opusfile and opusurl libraries provide a high-level API for decoding and seeking within .opus files on disk or over http(s).
opusfile depends on libopus and libogg. opusurl depends on opusfile and openssl.
The library is functional, but there are likely issues we didn't find in our own testing. Please give feedback in #opus on irc.freenode.net or at opus@xiph.org.
Programming documentation is available in tree and online at https://opus-codec.org/docs/