Decode next MPEG frame to internal buffer
or read a frame and return after setting a new format.
\param mh handle
\param num current frame offset gets stored there
\param audio This pointer is set to the internal buffer to read the decoded audio from.
\param bytes number of output bytes ready in the buffer
\return MPG123_OK or error/message code
Decode next MPEG frame to internal buffer or read a frame and return after setting a new format. \param mh handle \param num current frame offset gets stored there \param audio This pointer is set to the internal buffer to read the decoded audio from. \param bytes number of output bytes ready in the buffer \return MPG123_OK or error/message code