faster load time - audio and video seperately or in one file?

I've had issues in the past with slides with video files taking a long time to load.

In my current project I have slide layers with ~30 second video files on each layer. 

I always record my audio separately using audacity as  it's easier to edit, and I find narration recorded directly into articulate tends to be very quiet.

So now I have a choice of approaches - does anyone know which approach would be more likely to avoid long load times of the slide/slide layers

Approach 1: Have mp4 video files and mp3 audio file loaded onto the slide seperately

Approach 2: Combine my video and audio using a video editing software (replay or camtasia), produce this as an mp4 and put the combined mp4 file onto the slide?

This might be a totally obvious question to intuitively I'd think that 1 file would load faster than 2, but if the MP4 file is larger as it contains audio, maybe not?

Any insights appreciated. Thank you all.

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