127-mule-photos-new: pre-transcode pass + perf characterisation

Measured cold-cache behaviour: thumbnails ~2ms, HEVC video playback
12-21s TTFB because libx264 transcodes inline and serialised one
ffmpeg at a time. Sibling thumbs unaffected (~2ms during transcode).
With 11/45 .mov files already pre-baked, ~75% of clicks were cold.
Ran `photoprism convert` to bring sidecar coverage to 45/45; previously
cold videos now serve in ~2ms TTFB.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

containers/127-mule-photos-new.md

@@ -200,6 +200,32 @@ DELETE FROM auth_sessions WHERE user_name='dtoro';
 
 Stale sessions are dropped so a fresh OIDC login mints an admin token.
 
+**Video pre-transcode pass** (no upstream change — operational fix on
+this LXC). Only 11/45 `.mov` originals had a `.avc` sidecar; the rest
+forced 12–21 s inline libx264 transcodes on first playback, serialised
+one ffmpeg at a time. Measured cold vs warm:
+
+| Path                              | TTFB    |
+| --------------------------------- | ------- |
+| Thumbnail `fit_1280` (warm)       | ~2 ms   |
+| Video playback with `.avc` sidecar | ~2 ms   |
+| Video playback without sidecar     | 12–21 s |
+| Thumbnail GET *during* a transcode | ~2 ms (no sibling slowdown — 6-core LXC, ffmpeg ~6%/core, nvme util 0.01%) |
+
+Mitigation:
+
+```bash
+pct exec 127 -- docker exec -d pp-app /opt/photoprism/bin/photoprism convert
+```
+
+Walks the library, builds every missing `.avc` next to its original
+(`/photoprism/storage/sidecar/<year>/<month>/<name>.mov.avc`),
+idempotent on re-run, two ffmpeg processes in parallel. Took ~8 min
+to bring coverage to 45/45. Previously-cold videos verified to serve
+at ~2 ms TTFB after the pass. Future imports get AVC sidecars
+automatically as part of indexing; a re-run is only needed if videos
+ever land outside the indexer's path.
+
 **Folder tree** (upstream commits `8083328`, `505fef5`, `cfd85a1`).
 PhotoPrism's `path:` operator is exact-match by default but supports
 a `*` wildcard. Without it, every internal tree node (year folders,