Exporting slowness

I’ve been using Shotcut for a while now and I really like it. Here’s a question that’s been bugging me since I started using Shotcut.

I make a lot of videos and the videos are short ones - around 3 to 5 minutes. I load in the video, crop the ends so they are clean and I hit export. I’ve disabled the audio and I’m only exporting the video. I’m doing a two pass output and the video is done in around 4 minutes or less. Later, I’ll do another video at the same resolution and around the same duration and it will take 20 minutes with each pass taking 9 minutes. Later, I do another video of the same and it’s done in 4 minutes. Why do some take so long?

Does any know if a video card will make the export function faster? Currently I’m using the onboard graphics from my motherboard. My research came across some information on GPU which is graphics card related so I wonder?

You mention resolution all being the same. What about FPS?
To see your Frame rate, open a video, then click on Properties.

If you want to mute the audio, can you can so here as well, click on the audio tab and select none.
shotcut_2020-02-11_16-40-36

Example: Variable frame rate video.
2020-02-11_16-34-12

Example: Solid frame rate video.
2020-02-11_16-34-27

Does the Frame rate match the Video Mode setting?

Thanks for the reply @Hudson555x. The frame rate is constant at 25 - in other words, all my videos are exported with the same parameters.