Letterbox, or crop and follow
You have two choices. Post it landscape inside a vertical frame, which keeps the whole crowd but leaves bands above and below. Or crop to 9:16, which fills the screen but keeps only about a third of the width. Because your figure walks through the crowd after the first few seconds, a fixed centre crop can lose you: in the reference the figure is left of centre at about 4 seconds and near the right edge at about 12. If you crop, use an editor that lets you move the crop window to follow the figure.
