This is not my video, but I'm posting it here because it has an unusual McGyver'ed POV at the beginning, it's well-edited, and the trail looks like fun too.

It was done by the son of a non-DT riding friend. Here's what he said about it when I asked:
"I have a bunch of mounts that I use to get those shots. For the calf shots, we actually used a broken carbon handle bar to attach to the chain stay with zip ties (to a carbon rental bike... not the best choice haha but its not our bike!). The rear cog shot was done by attaching the camera to the chain stay facing backwards with a bar mount. The backwards shots are done by attaching the camera underneath the saddle facing backwards. The trail is Guardians in Upper Bidwell Park in Chico."

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Thus, if we are to understand the world, we should live somewhere between judgement and amazement — Alfredo Lopez Austin