Playback of MPEG4-container issues on WD MyBook

Searched and found some historical hits to playback problems but nothing more recent than 4-5 yrs old and none with identical issue.

Previously had a 3Tb Samsung D3 powered external HDD with libraries consisting of MPEG4 container video and MP3 music files held within. Connected to a Samsung TV via USB3 port. All good. All play fine.
Also have a WD MyCloud NAS attached over WiFi. Identical media library replicated (so x2 discrete copies for redundancy, but also serve different TVs in the household). All good. All play fine.

Ran out of space and thus replaced the Samsung D3 HDD with a 6Tb WD MyBook. Copied the libraries across devices and connect MyBook to Samsung TV via USB3. All good. All historical library files play fine.

Now add new MPEG4 container video files (codecs variations of both H264+ACC and also mpeg4+acc) to the new 6Tb MyBook HDD and TV says “file format not known”. Transfer the same files to the old 3Tb D3 HDD and they play perfect on same TV. Files also play from the WD MyCloud over WiFi.

All the old video files in the library were converted the identical metholody and play fine. Only new additional files to the MyBook HDD fail from i.e. file playback failure is only from the new 6Tb WD MyBook. Formatted to FAT32 etc as required by the TV. Approx 5000 video files in the library so not excessive. (+ about 35K music files)

Anyone have a clue as to why the external, powered WD MyBook USB3 HDD can’t feed the new video files when other devices function perfectly over both USB3 and WiFi please? And previous video files still work A-OK?
It’s def specific to this external HDD and have replicated it on x2 different Samsung TVs with x2 6Tb WD MyBooks (copied library to both and replicated the issue). So Definitely MyBook specific. Why would a HDD selectively fail to feed MPEG4 video files?

Any pointers appreciated, or to any links to other postings which I may have missed.
Many thanks team.

I’m curious, couple of questions

how did you manage to format a 6TB drive FAT32 ?

what partition table are you using on the 6TB ? MBR or GPT?

does the Samsung TV officially support (in the user manual specs) 6TB ? … i thought the max capacity for Smart TVs was 2TB ~4TB Max.

the 6TB can play all other container formats ? MKV, AVI, WMV play fine, but it won’t play MP4 ?

if you connect the 6TB to your PC … do the MP4 play ok ?

You got me doubting myself on the FAT format…and am not near the device for couple of days to check.
File plays fine when drive connected to PC. For use across multiple media players (well beyond TV alone) use MP4 container codecs only and not AVI etc. Can/will Handbrake a sample file and try. And will rip a previous DVD to that codec too.
But possibly the 4Tb max constraint by the Samsung TV is the simple answer after all. That would explain the most simple, single variable…i.e. same files play over WiFi DLNA but not via USB3. Will check when back next to the devices. And will do some googling in the meantime.
Thanks for the suggestion. Appreciated.

Now I’m back…Can positively confirm that the Samsung TV, which was not able to correctly read off an external USB3-attached 6Tb WD MyBook HDD, was because of the TV Linux OS not correctly recognising the single partition size, as you rightly suggested.

Despite searching the manuals, documentation and forums I couldn’t source the formal HDD limitation ( most search engine hits were too old or vague to be conclusive). Instead, I simply partitioned the HDD to x2 3Tb partitions (NTFS) and all is now working again, as previous. The specific files which were not correctly playing from the new 6Tb HDD, but were fine from both a DLNA My Cloud and/or the original 3Tb USB3 HDD, are now displaying perfectly from the newly partitioned 6Tb device. Simples.

Many thanks for the HDD partition sizing prompt which was the one aspect and variable which I hadn’t factored.