Ogg theora video transcodes sometimes come out at 1000 fps, with lots of duplicate frame markers to maintain the actual frame rate.
I'm not sure how well browser players handle that, but ogv.js currently tries to actuall draw 1000 frames per second and the result is very slow!
- ogv.js: https://github.com/brion/ogv.js/issues/349
- ffmpeg2theora: not yet filed
Note both of these were uploaded through videoconvert on tool labs, so the webms produced there might be funky. The Latourell Falls video was shot on my Nexus 5x Android phone and uploaded from the .mp4 source.
Note also that webm/vp8 doesn't specify a frame rate the same way ogg theora does; frames are simply positioned in time. So there may be something funky about the webm files, and there may be something funky with the ogg conversion.