I just recently had to regenerate my preview thumbnails and after doing so Plex started generating these index-sd.bif.tmp files for me as well. After generating these thumbnails for a week there are now 36.3GB worth of these .tmp files and there are 7451 of these files in total. This is after 1 week.
Even after deleting all the preview thumbnails (again), these files were not removed. I was checking in how the thumbnail generation was coming along and noticed my ‘Media’ folder where the thumbnails are stored is now 15GB larger than it was before, even though before this I had thumbnails for every media item in my library.
Below are some stats from before I started rebuilding my thumbnails. This shows that there were 1030 index-sd.bif.tmp files in total before my rebuild and the oldest file is from 29th Oct, 2024. I started my rebuild on 21st Mar, 2025 (which is why that’s the ‘maximum’ date).
This suggests that it’s been an issue at least as far back as 29th Oct, 2024. Interestingly enough, I found a Plex update log with that same date:
Oct 29, 2024 04:05:03.117 [5448] INFO - Plex Update Service Launcher v1.41.0.8994-f2c27da23 - Microsoft PC x64-x64 - build: windows-x86_64
Oct 29, 2024 04:05:03.118 [5448] INFO - Windows version: 10.0 (Build 19045), language en-US
Oct 29, 2024 04:05:03.118 [5448] INFO - 12 3693 MHz processor(s): Architecture=9, Level=25, Revision=8448 Processor Identifier=AMD64 Family 25 Model 33 Stepping 0, AuthenticAMD
Oct 29, 2024 04:05:30.199 [22704] ERROR - Bundle Exit Code: 0 - The operation completed successfully.
The update started on Oct 29, 2024 04:05:03 and the oldest index-sd.bif.tmp file was created on Oct 29, 2024 04:18:30 (13 minutes after the update).
This log lists the old/previous version as v1.41.0.8994, which was released on 26th Sep, 2024. Unfortunately these logs don’t list the version it updates to (only the current version) and these “Update Service Launcher” logs are the only logs I have that go as far back as that.
But fret not. With the power of deduction we can figure out that there was only one update in that one-month window that could have caused this: v1.41.1.9057 (link to release notes).
The update was released to the stable channel on Oct 24, 2024 (five days before my update). Keep in mind that I only update PMS manually, so the release dates don’t always match up with when I actually update PMS.
So let’s see what changes were made to thumbnail generation in that version:
- (Preview Thumbnails) Preview thumb generation can sometimes fail when using keyframes only (PM-1601)
- (Preview Thumbnails) Preview thumb generation never stops retrying after failing (PM-1601)
Seems like something was indeed changed with preview thumbnail generation in that update. Of course, this is not conclusive evidence, but the details seem to match up too perfectly. Hopefully we can get some feedback from Plex regarding this issue.
I would have never stumbled across this issue if I didn’t go snooping into the thumbnails folder. I suspect this issue is a lot more wide-spread, but people simply aren’t aware that it’s an issue and that their ‘Media’ folder is getting bloated unnecessarily. This is especially killer if you decide to regenerate the thumbnails after that update (as I did).
I would urge anyone that has had their current PMS install from before 24th Oct, 2024 to check what date their oldest index-sd.bif.tmp file is from. It’s also possible you still have the Plex Update Service Launcher.log file from that time (which is where I got the logs from). On Windows, these logs can be found under %LOCALAPPDATA%\Plex Media Server\Logs. Matching up these two data points across multiple users could help us figure out if it was indeed an update that caused this.
On Windows, to check the date of your oldest index-sd.bif.tmp file, the simplest way is to download a utility called Everything by VoidTools, which indexes your whole filesystem in a couple minutes and lets you search, well… everything. Then you just enter the search term "%LOCALAPPDATA%\Plex Media Server\Media\" .bif.tmp and sort by ‘Date Modified’ or ‘Date Created’. It’s actually a great tool overall, if you decide to keep it.
Another option would be to write a small batch script, but I’m not sure whether Plex appreciates random batch commands on their forums, so I’m not going to post that here.
