So just as an update, I got an answer from another source (https://superuser.com/questions/1462076/25-of-my-mp4-have-error-reading-header-in-ffmpeg-opencv-but-videos-all-pl).

Basically, it sounds like some of the metadata for the videos saved from my camera isn't quite standard. The answer at the link above explains better than I ever could, but would be grateful if someone from Reolink could take a look and see whether that can be fixed / changed in a firmware update. I've got a workaround for now, and sounds like there will be a patch to FFMPEG shortly to make it tolerate this type of metadata, but would be great if the camera produced "standard" .mp4 videos by default.

I've had a long-running problem with videos saved from my 411S camera via FTP to a local Raspberry Pi server. The videos all play fine, but a large proportion (maybe 25%?) have errors in the video headers. It's not been too much of a problem in the past as my software has seemingly tolerated the errors, but a new version is more strict and just won't open the videos any more.

If I try to open one of the videos in FFMPEG, I get [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7ff492000400] error reading header [path]: Operation not permitted.

I've put an example video here: https://www.dropbox.com/s/tu4ddegh6yn05nu/ErrorReadingHeader.mp4?dl=0

Grateful for any insight into what's going wrong - the file is unmodified (other than being renamed and uploaded to Dropbox) since being saved onto my computer using the FTP feature of the Reolink 411S.

PS - I've just updated the firmware to the latest version, and reset all settings / configuration, but no improvement...

Thanks!