我觉得是不能同时在线超过25个客户端

是的，确实不明白，关键到了数量是谁来限制

比如看到5人拼团，这样就会有5个服务端，如何限制一个服务端只能用5个设备

Emby Premier的购买页面上有Emby Premiere Terms of Service，关于设备数量的问题里面有描述。
硬件设备+系统+软件对应一个id，总id数量最大25（服务端是否占用一个id额度我不清楚）。同一台机器同一个系统安装了多个emby客户端，也会对应多个id。超过25个id后，新来的id无法使用Emby Premier功能。
另外，系统统计25个id是有一个滚动的时间窗口的，最后一次访问server的时间不在此窗口期内的id不会被统计在内，此窗口期用户无法查看具体范围。所以不用担心很早以前的id占用名额。
附原文：
Premiere Devices: Emby Premier shall allow for a certain amount of total devices per subscription for access to Premier only features and apps. Unless otherwise indicated on the website, Emby Premiere shall be limited to 25 Devices per Premiere key.
A "Premiere Device" is defined as any mobile, computer, or other electronic device which registers with the Emby server with a unique "device id". The device id is a uniquely generated id that is dependent on both device model, OS version, and application. Each unique device id shall be counted as a separate Device. It is possible that a single machine (whether mobile, desktop computer, or otherwise) with multiple applications installed on the machine may register as a new device id per application. In this event, each unique device id will be counted as separate devices.
The Premiere Device shall be granted access to Premiere applications and services for the Subscription Term. The system will automatically manage the devices as being granted Premiere Device access throughout the Subscription term on a rolling date-of-access basis. The term for this rolling period is to be determined by the system and may change from time to time without notice. Any devices in excess of the permitted number or upon expiration of the given Subscription Term may no longer have access to any Premiere functionality, apps, or services.

是任何一个登录服务端加上客户端。比如手机里有emby app登录，infuse登录，网页登录，就算3个设备。你可以在服务端里面看到信息

它是根据硬件号还是ip号？？ 比如同一台机器不同地点登录chrome版本的 是算一个么？