Function vmeta_frame_write 

pub unsafe extern "C" fn vmeta_frame_write(
    buf: *mut vmeta_buffer,
    meta: *mut vmeta_frame,
) -> c_int

Write frame metadata. This function fills the supplied buffer with the serialized metadata, according to the metadata type. The size of the data written is returned through the pos field in the buf structure. The buf structure must have been previously initialized using the vmeta_buffer_set_data() function with a previously allocated buffer and its size. The pos field in the buf structure does not need to be 0 prior to calling the function (i.e. data can already be present in the buffer). The ownership of the buffer stays with the caller. @param buf: pointer to the buffer structure (output) @param meta: pointer to the frame metadata structure @return 0 on success, negative errno value in case of error