Import your newly downloaded .webm overlay and your action camera footage into your video editor (Premiere Pro, DaVinci Resolve, Final Cut, etc). The .webm file natively features an invisible/transparent background.

Place the Verdant Speed overlay on the track above your action camera footage. Stretch (or time-remap) the Verdant Speed video so its start and end perfectly align with the beginning and end of the GPX measured portion of your action camera video. You can drag and position it in any corner of your frame!