Repair inherited Dolby Vision cache metadata

README.md

@@ -58,7 +58,9 @@ Cached video is H.264 High Profile, 8-bit `yuv420p`, CRF 18, capped at 15 Mbps.
 Resolution and frame rate are preserved. Existing audio, subtitles, chapters,
 and Matroska attachments are copied. Ten-bit SDR is converted with
 error-diffusion dithering; sources carrying explicit HDR10 or HLG transfer
-metadata are tone-mapped to BT.709 SDR.
+metadata are tone-mapped to BT.709 SDR. The filtered video is mapped as a new
+stream so source-only Dolby Vision configuration data cannot leak into H.264
+outputs.
 
 The fixed source blacklist is:
 
@@ -99,6 +101,22 @@ partials and orphan files. Atomic symlinks always point to either an original or
 a completed cache file. If the cache mount marker is absent, the worker refuses
 to start.
 
+## Upgrading from v1.2.0
+
+Version 1.2.1 uses a v4 cache profile. Before starting the new worker, stop the
+old worker and migrate its manifests:
+
+```bash
+docker compose stop pretranscode
+docker compose run --rm pretranscode migrate-v4
+```
+
+The migration re-probes immutable sources, updates every valid v3 manifest, and
+creates a state backup. Cached H.264 streams that inherited Dolby Vision
+configuration data are repaired with a lossless stream-copy remux; video is not
+re-encoded. Other cached media files are not rewritten. The command refuses to
+run while Jellyfin reports active playback.
+
 ## Migration
 
 Copy or recreate these resources on the destination: