When I record videos, the drone stops / splits files at approximately 3.8Gb size.    This is tiny bit odd to be for 2 reasons: 1) exFAT  - the fs on the micro sd card - supports files larger than 4Gb, and 2) 3.8 is not quite even 4 Gb.
In addion, it is not down to byte consitent at that size - 3.8Gb - and it varies every single time seems, by some bytes ....  Is this normal / not? Why does it split at this size? Why is exact size not constant ?

These are sizes I have now for example :

1
Size : 3.80 GB (4,090,293,817 bytes)
Size on disk : 3.80 GB (4,090,363,904 bytes)
2
Size 3.80 GB (4,090,108,315 bytes)
Size on disk : 3.80 GB (4,090,232,832 bytes)
3
Size : 3.80 GB (4,090,100,663 bytes)
Size on disk : 3.80 GB (4,090,101,760 bytes)

Also, I think I had to re-start recording video each time max is riched, but not sure on this ... . And few times it seemed gimball crashed at the max.

What does your do?

It is quite normal, and you should not have any problem joining the two files in an editor. It has nothing to do with the format scheme, it is a hangover from many years back when there were different duty rates on imported devices, depending upon whether they were cameras or recorders. Cameras were at a lower rate of duty, but technically were not permitted to record files greater than 4 GB, whereas recorders could produce longer files and carried a higher rate of duty.

None of that is relevant these days in most parts of the world, but some places still apply those rates. The aircraft should not stop recording at the boundary, but simply start another file.

Geebax Posted at 1-1 22:20
It is quite normal, and you should not have any problem joining the two files in an editor. It has nothing to do with the format scheme, it is a hangover from many years back when there were different duty rates on imported devices, depending upon whether they were cameras or recorders. Cameras were at a lower rate of duty, but technically were not permitted to record files greater than 4 GB, whereas recorders could produce longer files and carried a higher rate of duty.

None of that is relevant these days in most parts of the world, but some places still apply those rates. The aircraft should not stop recording at the boundary, but simply start another file.

Thought split point done before 2^^32 (4,294,967,296) is reached, was to ensure backward compatibility?  
Allowing computer systems with older file systems, or older video editors to work.

Geebax Posted at 1-1 22:20
It is quite normal, and you should not have any problem joining the two files in an editor. It has nothing to do with the format scheme, it is a hangover from many years back when there were different duty rates on imported devices, depending upon whether they were cameras or recorders. Cameras were at a lower rate of duty, but technically were not permitted to record files greater than 4 GB, whereas recorders could produce longer files and carried a higher rate of duty.

None of that is relevant these days in most parts of the world, but some places still apply those rates. The aircraft should not stop recording at the boundary, but simply start another file.

wow, cannot believe tax / duty rate affected recording length of a video.

The issue about recorder stopping, may be related to some internal crash / restart.  But i notice it I would say fairly often  (if not always) at about video file limit size.  In fact, could that cause the slightly different file size each time ...?  If it's crashing right at the boundary / soft bug.

Couple of times I thought a bird attacked it in the air, as the drone stopped and video stopped, and gimball / cam feed went funny / side ways, showing rotors somehow ..  
I thought it was a bird attack  (there is a chance of course... )but, the drone came back and there was no damage / traces of it.

And that happened a few times now.

Hi. I am sorry for the trouble and thank you for reaching out to DJI Forum. With regards to this concern. The maximum file size of FAT32 is 4GB. Hence, a file that is larger than or equal to 4GB will be divided, otherwise, the file may be lost or abnormal and cannot be read. Although exFAT allows a larger file size, the larger file may be damaged due to abnormal power-off and SD card removal, or even cannot be recovered. So the storage of the camera is 4GB regardless of the file systems. So it is normal the video will be split if it reaches 4GB. Thank you.

Geebax Posted at 1-1 22:20
It is quite normal, and you should not have any problem joining the two files in an editor. It has nothing to do with the format scheme, it is a hangover from many years back when there were different duty rates on imported devices, depending upon whether they were cameras or recorders. Cameras were at a lower rate of duty, but technically were not permitted to record files greater than 4 GB, whereas recorders could produce longer files and carried a higher rate of duty.

None of that is relevant these days in most parts of the world, but some places still apply those rates. The aircraft should not stop recording at the boundary, but simply start another file.

I thought the problem was with the MPEG licensing kicking in at that size rather than duty rate, but I've never seen an entirely satisfactory answer -- some claimed this was to save the sensor from overheating, etc. ¯\_(ツ)_/¯

At any event it seems now this is a hard limit set by DJI in order to minimize data loss frustrations.