Not sure it’s relevant but I experienced EXACTLY this type corruption of video on an older version of cockpit/BlueOS. You can see it in this video I uploaded to the Adventure log ages ago (around the 8:22 mark).
I thought at the time that it seemed to be due to a lag between when I pressed record on a touch screen in Cockpit and the indicator showing recording had started. This lag caused me to tap quickly again and I presumed it might have opened two instances/files at the same time but this was a amateur guess rather than a expert diagnosis 
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