如何在discord.py中记录用户离开和加入语音通道的时间？

import discord
from datetime import datetime

client = discord.Client()

@client.event
async def on_voice_state_update(member, before, after):
    if before.channel is None and after.channel is not None:
        # 用户加入语音通道
        timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
        print(f"{timestamp} - {member.name} 加入了语音通道 {after.channel.name}")

    elif before.channel is not None and after.channel is None:
        # 用户离开语音通道
        timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
        print(f"{timestamp} - {member.name} 离开了语音通道 {before.channel.name}")

client.run('YOUR_BOT_TOKEN')