T-SQL to retrieve records after comparing two columns of the same table

try this,

with cte
as
(
select [KEY],start_datetime,end_datetime,1 as recodringno from [dbo].[recordings] where [KEY] =1
union all
select a.[KEY],a.start_datetime,a.end_datetime
,case when DATEDIFF(MINUTE,b.end_datetime,a.end_datetime)>3 then b.recodringno+1 else b.recodringno  end

as recodringno from 
[dbo].[recordings] a 
inner join cte b on a.[KEY]=b.[KEY]+1 

)
select 'recodring'+cast(recodringno as varchar(10)) as recodringno
,MIN(start_datetime)start_datetime,MAX(end_datetime) end_datetime from cte group by recodringno

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