To create a progress bar, begin by dragging a colored rectangle of your choice onto the top video track of your timeline. To do this, select the backgrounds tab and then select solids in the left-hand menu. Next, you’ll want to expand the clip on your timeline so it lasts for the entire duration of your video. This will cause your entire video to be covered by the color you chose. To fix this, double-click the clip to open the editor menu. Next, in the transform tab, scale the rectangle so that it’s at the exact width of your preview screen and drag it to the bottom (so that only a sliver is showing). You can select the checkboxes for Show Grid and Snap in the top-right corner above the preview screen to make this process a bit easier.
Once you’re set, select Save Changes and go one tab to the right to create the animation. Select the start arrow and then adjust the progress bar rectangle so that only a sliver is showing in the bottom-left corner. You’ll want to remember the X coordinate and type that in so that the animation will stay at the same level for the entire duration. When you click end, the progress bar should cover the entire width of the bottom of your screen. Click Save Changes and you’re all set!