Netflix 4K HDR needs a minimum of about 25Mbps (50Mbps+ comfortable); YouTube 4K needs around 20Mbps. Two people streaming 4K at once really wants an NBN 100+ plan. If you're already above these numbers and still buffering: switch to Ethernet, check nothing else is hogging bandwidth (background downloads, torrents), and confirm during peak hours (7–10pm) whether it's an ISP congestion issue rather than your home setup.

Netflix 4K HDR最低约需25Mbps(50Mbps以上比较舒服)；YouTube 4K大约需要20Mbps。两个人同时看4K建议NBN 100以上。如果带宽已经够但还是卡：换成有线连接，检查有没有其他东西在偷偷占带宽(后台下载、种子)，再确认晚高峰(7-10点)是不是ISP拥堵而不是家里设置的问题。