[FEATURE] Render GPX to MP4 without source media file

[tarampampam]

Is your feature request related to a problem? Please describe.

Hello there, and thank you for your project! Allow me to explain my situation to help you better understand why I'm requesting this feature. I'm a happy user of the GoPro 11, which unfortunately lacks a built-in GPS feature. To compensate, I record a GPX file using an app on my mobile phone, which I always have with me when riding my bike.

After each ride, I'd love the option to render the GPX file into an MP4 format. This way, I could easily combine multiple short recorded videos into one cohesive video in my video editor and add an overlay with real-time data such as speed and altitude.

Describe the solution you'd like

./gpx2video -v -g ./path/to.gpx -l layout.xml -o output.mp4 video # without --media flag