It's a great picture, just jittery.
TrueYep, firm ride transmits to the camera. It's a great picture, just jittery. But like I've commented to others who have various issues such as color accuracy or dashboard glare (from any cam), it's not a huge thing because it's not like you're watching it for an hour, you just want it to capture any events - which it does.
Actually I think it's too firm. Every vibration seems to be transferred to the camera. Not withstanding the poor upload quality, you can see the shaking in this video. Get past the 1:25 mark
www.youtube.com/watch?v=rgQAFKGD37c&feature=youtu.be
that's your issue, stick the mount directly to the glass using the provided 3M and the picture won't jitter, even your suspension is hard or you have low profile tyres or whatever the camera will move in sync with the vibration of the vehicle and the picture won't jump around, you can get away with more movement in something that rides a bit smoother perhaps but adhere it to the window directly for best resultsit's just to the right of the rear view mirror. Velcro'd with Dual Lock (3M extreme) rather than the double sided sticky tape - this make it easier to remove than the slide mount. Rahter than being toofirm to the windshield, maybe it's the Dual lock that's shaky and not secure enough. I'd check it out tomorrow but i'm taking the Infiniti so it would be a good comparison.
Very likely the cause. I had my GC mounted with industrial strength Velcro and would get the same type of 'jitter' in the video. When I switched to the dual lock it went away and the video is very stable. The A118-C cameras (front and rear) in my wife's Honda are also mounted with dual lock and are stable as well. Your Miata has a shorter wheel base (and probably a stiffer suspension) than either of our vehicles so the dual lock may not be holding firm enough.Ah, Dual lock extreme / Velcro probably won't give you the best stability results. You think the normal mount is too firm? I'd try using the regular mount, get a spare if you have two cars.