It sounds like that the lecturer is saying
i wanted to say
is it because the lecturer made this video in the past and the audience necessarily watch the video later?
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No. It's a common phrase in this context, and suggests diffidence or tentativeness. The implication is something like "I wanted to say this, if that's all right with you" - it is the conditional use of the past rather than a true past.
It doesn't necessarily signal that the speaker is genuinely feeling diffident or tentative, but it somehow makes it seem more polite.