How to rotate the live recorded video stream to a maximum limit?

Is it possible to limit the length of live recorded video stream to N minutes/MegaBytes by SSAS in FMS?

- Yes very much. When you use additional parameters of Stream.record() API, you can limit by time as well as by size - please see docs here:

http://help.adobe.com/en_US/flashmediaserver/ssaslr/WS5b3ccc516d4fbf351e63e3d11a11afc95e-7e42.html#WS5b3ccc516d4fbf351e63e3d11a11afc95e-7f35

f the aggregate size of stream outcomes the limit,always make the recorded video file the last N minutes/MegaBytes of the live show?

- FMS does not yet support rolling window like above - but there is workaround for it. You can choose "raw" format of recording the content. When you choose to record in raw it records streams in set of small files (time or size of which you can control using MaxFlushTime/MaxFlushSize). So now you can write your own external script to delete older files and keep only relevant files. Also key thing to note here is that you need to develop smart client who will handle cases like seeking to older value and file not being present or pausing for longer time.