Hey Wasin, to understand how Selenium scripts can be written for Flash testing, refer to the following code snippet:
import org.openqa.selenium.firefox.FirefoxDriver;		
import Flash.FlashObjectWebDriver;		
public class Flash {				
    public static void main(String[] args) throws InterruptedException {								
  	// Open firefox browser		
	FirefoxDriver driver = new FirefoxDriver();			
  	// Maximize browser		
	driver.manage().window().maximize();		
  	// Under Flash jar file there is separate FlashObjectWebDriver class		
	FlashObjectWebDriver flashApp = new FlashObjectWebDriver(driver, "myFlashMovie");		
  	// Pass the URL of video		
	driver.get("https://youtu.be/FRn5J31eAMw?si=COF6n-bgsaJg5HuR");			
	Thread.sleep(5000);		
  	flashApp.callFlashObject("Play");			
  	Thread.sleep(5000);		
	flashApp.callFlashObject("StopPlay");			
	Thread.sleep(5000);		
	flashApp.callFlashObject("SetVariable","/:message","Flash testing using selenium Webdriver");
    System.out.println(flashApp.callFlashObject("GetVariable","/:message"));						
  }		
}