On TV, one speaker too many? (5-4)

I believe the answer is:

voice-over

I'm a little stuck... Click here to teach me more about this clue!

'on tv one' is the definition.
The definition suggests a singular noun which matches the answer.

'speaker too many?' is the wordplay.
'speaker' becomes 'voice' (I've seen this before).
'too many?' becomes 'over' (I've seen this in other clues).
'voice'+'over'='VOICE-OVER'

Can you help me to learn more?

(Another definition for voice-over that I've seen is " Narration to a film".)

Want a hint initially instead of a full solution? Install my app