Automatic previews (capture and first view), the thumbnail job, the
legacy gallery routes and the history route write <stem>_thumb.webp
(or .jxl/.jpg) with the configured quality and size limit, for images
and videos alike: video frames, ffmpeg's included (a PNG on stdout,
never upscaled), and the placeholder are encoded like images.
Listings, duplicates, enrichment, the autotag scan and the history
route show any preview the file owns, the current format first, so
older _thumb.png previews keep working until converted. A request for
an older name answers the current preview. Previews are served with
an explicit image/webp or image/jxl type and the same cache headers.
The plan and status count missing, outdated (another format) and
ready previews; the missing job never writes beside an outdated one.
Removing a file removes its previews in every format; the clear
removes .webp and .jxl too. Encoder processes are killed at shutdown.
A preview is only a placeholder: inspection refuses paths under
thumbnails/ and always reads the original, and the inspector cover
accepts the listing's preview in any format the file owns.
Thumbnail format (webp default, jxl, jpeg), quality (1-100, default 80)
and size limit (128-2048 px, default 512) are server settings in the
config.json thumbnails section, saved with the settings revision. The
never-read gallery thumbnail_size is gone: older saves wrote its unused
default 256 into config.json.
One module names previews (<stem>_thumb.webp/.jxl/.jpg) and finds the
preview a source owns, preferring the configured format; legacy names
are still found. The encoder module writes every preview atomically and
verifies it decodes. JPEG XL needs no new dependency: Pillow (natively
or with pillow_jxl), ffmpeg with libjxl, or cjxl; without one the
settings refuse jxl (400 jxl-unavailable) and GET says why. Encoder
processes are tracked, bounded and killed at shutdown.
Vito Sansevero