Popular source of documentaries that is not mainstream (5)

I believe the answer is:

indie

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'not mainstream' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'popular source of documentaries that is' is the wordplay.
'popular' becomes 'in'.
'source of' suggests taking the first letters.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
The first letter of 'documentaries' is 'd'.
'in'+'d'+'ie'='INDIE'

Can you help me to learn more?

(Other definitions for indie that I've seen before include "Specialist record company" , "Non-mainstream film company" , "Independent record company" , "Non-affiliated record label or pop group (colloq.)" , "minor label" .)

I've seen this clue in The Telegraph.

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