[Bug]: Event previews are sometimes not created

[leccelecce]

Checklist

• I have updated to the latest available Frigate version.
• I have cleared the cache of my browser.
• I have tried a different browser to see if it is related to my browser.
• I have tried reproducing the issue in incognito mode to rule out problems with any third party extensions or plugins I have installed.
• I have asked the AI at https://docs.frigate.video about my issue.

Describe the problem you are having

api/events/:event_id/preview.gif is sometimes throwing an HTTP 500. Looking at the Frigate error log, it seems it can't find something it expects in the DB. The same issue is visible in the UI - the thumbnail appears, but hovering over it doesn't play the GIF.

I've not found a pattern yet - it seems to affect multiple cameras (Hikvision, Reolink, Protect) - but not consistently i.e. the same camera will sometimes.

Happy to have a look through code for possible reasons to explore further if you can point me towards what writes the event previews?

Steps to reproduce

n/a

Version

0.17.0-f0d69f7

In which browser(s) are you experiencing the issue with?

No response

Frigate config file

n/a

docker-compose file or Docker CLI command

n/a

Relevant Frigate log output

...
2026-03-08 19:11:48.064702532    File "/opt/frigate/frigate/api/media.py", line 1487, in event_preview
2026-03-08 19:11:48.064704627      return preview_gif(request, event.camera, start_ts, end_ts)
2026-03-08 19:11:48.064706664             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2026-03-08 19:11:48.064708786    File "/opt/frigate/frigate/api/media.py", line 1520, in preview_gif
2026-03-08 19:11:48.064710265      .get()
2026-03-08 19:11:48.064711830       ^^^^^
2026-03-08 19:11:48.064728590    File "/usr/local/lib/python3.11/dist-packages/peewee.py", line 7298, in get
2026-03-08 19:11:48.064730894      raise self.model.DoesNotExist('%s instance matching query does '
2026-03-08 19:11:48.064733319  frigate.models.PreviewsDoesNotExist: <Model: Previews> instance matching query does not exist:
2026-03-08 19:11:48.064737901  SQL: SELECT "t1"."camera", "t1"."path", "t1"."duration", "t1"."start_time", "t1"."end_time" FROM "previews" AS "t1" WHERE (((("t1"."start_time" BETWEEN ? AND ?) OR ("t1"."end_time" BETWEEN ? AND ?)) OR (("t1"."start_time" < ?) AND ("t1"."end_time" > ?))) AND ("t1"."camera" = ?)) LIMIT ? OFFSET ?
2026-03-08 19:11:48.064740885  Params: [1772990625.184701, 1772990633.158074, 1772990625.184701, 1772990633.158074, 1772990625.184701, 1772990633.158074, 'front_porch', 1, 0]

Relevant go2rtc log output

no errors

Operating system

Debian

Install method

Docker Compose

Network connection

Wired

Camera make and model

Hikvision

Screenshots of the Frigate UI's System metrics pages

n/a

Any other information that may be helpful

No response

[inkeep-ai-assistant[bot]]

Based on the error you're experiencing, the issue appears to be that Frigate cannot find a matching preview record in the database for the event's time range(1). The error frigate.models.PreviewsDoesNotExist indicates that when the API tries to retrieve the preview GIF, it's querying the previews table but finding no matching entry for that camera and time period(1).

This is a known issue that has been reported before(1). The error occurs when the API endpoint /api/events/:event_id/preview.gif is called, but the corresponding preview file hasn't been generated or the database entry is missing(1).

Some events may not have previews created if:

• The preview generation process failed or was interrupted
• The event duration or timing doesn't align with when preview segments are created
• There are gaps in the preview recordings for that time period

The same underlying cause affects both the API endpoint and the UI hover behavior you're seeing(1). When you hover over a thumbnail in the Review panel and see a black square with a "Preview not found" message, it's because the preview data is missing from the database(1).

For troubleshooting, you might want to check your retention settings for recordings, as preview generation depends on having the underlying recordings available(2)(3). The retention mode configuration affects whether recordings are kept based on motion or all the time(2)(3).

📚 Sources:

1. Internal server error when calling API for event_preview.gif and review_preview.gif
2. Full Reference Config
3. Create event via API and record for 5s - can't find event in frigate

---

Have another question? Just tag @inkeep.

[hawkeye217]

Looks like we should probably just put a try/except around that db select call and return 404.

[hawkeye217]

Fixed in #22331

[hawkeye217]

So previews are generated in frigate/output/preview.py by the PreviewRecorder class, which caches frames and triggers FFMpegConverter to encode them into MP4 segments on hour boundaries. The preview record is inserted via Previews.insert(payload).execute() in frigate/comms/dispatcher.py:127 (handle_insert_preview()), called after the FFmpeg conversion completes (triggered from frigate/output/preview.py:131-141). Old previews are deleted in frigate/record/cleanup.py:209-267 based on recording retention policy - if a preview doesn't overlap with any kept recording, both the MP4 file and DB record are removed.

[leccelecce]

So is there not expected to be a preview for an event in the UI if we haven't passed an hour boundary yet?

[NickM-27]

There is an in-progress preview with the individual frames, not an encoded one

[leccelecce]

So the unencoded previews are built at the top of the hour from files in /tmp/cache/preview_frames from what I can see. Given /tmp is a tmpfs mount, presumably restarting the container wipes this (not sure if restarting via Frigate's own command also would).

I'm yet to confirm exactly but I'm wondering if the missing previews I'm seeing are from where I've restarted the container. It doesn't feel quite right though.

If it is correct that restarting loses previews for the current hour - I think I'm willing to have the slight disk overhead of preview .webp files being written to disk rather than tmpfs, in the interests of not losing previews during a restart. Still doing some digging but - interested in your views on whether you see scope to change this? If not I guess I can look at mounting the subfolders of /tmp except the preview area, and mounting that to disk somewhere.

I probably need to be a bit more debugging to understand why I have missing previews as well - the 19:00 and 20:00 files below look to be too short for reasons I need to investigate; pretty sure no restarts around those times.

-rw-r-----+ 1 root root 4166390 Mar  8 15:00 1772978400.162643-1772982000.173782.mp4
-rw-r-----+ 1 root root 4060672 Mar  8 16:00 1772982000.173782-1772985600.02202.mp4
-rw-r-----+ 1 root root 4056453 Mar  8 17:00 1772985600.02202-1772989200.195043.mp4
-rw-r-----+ 1 root root 2075588 Mar  8 18:00 1772990960.397927-1772992800.062435.mp4
-rw-r-----+ 1 root root  299029 Mar  8 19:00 1772996139.912457-1772996400.108554.mp4
-rw-r-----+ 1 root root  534444 Mar  8 20:00 1772999528.578176-1773000000.01922.mp4
-rw-r-----+ 1 root root 4025097 Mar  8 21:00 1773000000.01922-1773003600.166142.mp4
-rw-r-----+ 1 root root 4258117 Mar  8 22:00 1773003600.166142-1773007200.155052.mp4

[NickM-27]

if Frigate is restarted on its own then it will move the files to a disk folder automatically, and then move them back when it starts up

[leccelecce]

Ok interesting thank you, hadn't found that bit yet.

I think then I need to figure out why some of my preview MP4s are truncated. Will do some digging.