Identify whether chapters or preview pictures are missing
Jellyfin distinguishes chapter markers from chapter images. A video can show timeline chapters while the small preview images are disabled or have not been extracted. Begin with one known video and note exactly what is absent: the chapter positions, the preview pictures or both.
Inspect the same item in the client you intend to use. A screenshot of a different application is not a reliable expected result for your combination. Keep the media file unchanged during the comparison, because replacing it with a different encode may also change the embedded chapter information and remove the useful baseline.
Review the setting for the affected library
Chapter-image extraction is configured per library in Jellyfin. Open the settings for the library containing the test video and inspect its Chapter Images options. Enabling a feature in another library does not establish that this item is covered. Record the relevant setting before changing it.
The documentation separates enabling chapter images from choosing extraction during the library scan. Decide which behavior you actually want. A household that frequently imports large batches may prefer to understand the separate extraction task before adding that work to every scan. The choice should reflect the server’s workflow rather than an assumption that every optional feature is free.
Compare the extraction task with the ordinary scan
Jellyfin documents a separate Extract Chapter Images task; the library option can move that work into Scan Media Library. Image extraction can be computationally intensive. If scans became much slower after a setting change, preserve the timing and the setting as evidence instead of immediately blaming metadata providers or storage failure.
Use a small library or limited representative import for your observation. Allow the appropriate task to finish, then inspect the same item’s chapter previews. Do not repeatedly launch additional scans while the previous work is still being assessed. Record task completion and the client result separately, since a scheduled task finishing and a client displaying previews are different checkpoints.
Keep generated preview settings proportionate
The developer documents an interval option for generated chapters when none are detected and a resolution option for preview images. Avoid extremely small intervals or unnecessarily large previews without a concrete need. These images serve a small navigation preview, not the full-screen movie picture.
After the task completes, test seeking around the known item and confirm the preview corresponds to the intended position. If the client still shows no image, record the client version, library setting and task result. The expected outcome is useful navigation metadata with an understood extraction route, not a promise that chapter settings improve video quality or real-time streaming performance.
Questions answered
Do visible chapter markers prove chapter images are enabled?
No. Jellyfin documents these as separate things. Chapter markers may appear while preview-image extraction is disabled.
Why did a library scan become slower after enabling previews?
Extraction can be computationally intensive. Check whether it was configured to run inside the library scan rather than through the separate image-extraction task.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.