MultiView

MultiView is a Fabric add-on for Flashback. It takes multiple .flashback replays recorded by different players from the same Minecraft session and merges them into one unified replay — an "omniscient observer" view containing the union of every chunk, entity and event seen from any POV.

What it does

Each player records their own POV using Flashback. MultiView aligns the recordings tick-by-tick and merges them into a single replay that behaves as if a single observer with unlimited render distance had recorded everything.

• All explored chunks from every POV are present in the merged replay.
• All recording players are visible at the same time.
• All entities and events seen by at least one POV are kept.
• Free Camera to roam, Spectate Player to follow a specific recorder.

Use cases

• Content creators — SMP recaps, PvP tournaments, machinima with multi-angle coverage.
• Server staff — multi-angle review of incidents and anti-cheat investigations.
• Cinematographers — free camera through a multiplayer scene with no info loss.

Quick start

1. Each player records their POV with Flashback during the same session.
2. Collect the produced .zip files into your own <gameDir>/flashback/replays/ folder.
3. Launch Minecraft with Flashback + MultiView installed.
4. Click the camera icon → Select Replay.
5. Tick the checkbox at the right of each replay you want to merge (minimum 2).
6. Click Merge N Replays in the top-right.
7. Wait for the progress screen to finish.
8. merged_<timestamp>.zip appears in the list — open it like any other replay.

Chat-only fallback (e.g. when you want to script merges):

/mv merge <source1> <source2> <output>

Compatibility

Minecraft	Fabric Loader	Flashback	MultiView version
1.21.9 / 1.21.10	0.19.2+	0.39.x	0.3.2+mc1.21.9
1.21.11	0.19.2+	0.39.4	0.3.2+mc1.21.11
26.1 / 26.1.1 / 26.1.2	0.19.2+	0.40.0	0.3.2+mc26.1

Requires Java 21 on 1.21.x and Java 25 on 26.1+. Fabric API is required.

Features

• N-way merge of Flashback replays from the same session.
• Tick-perfect time alignment via ClientboundSetTimePacket, with a fallback on metadata.name.
• Cross-source deduplication — chunks (SHA-256 128-bit content hash), player info updates, system chat by content, entity moves.
• Multi-dimension support — secondary POVs keep their dimension changes recorded as markers.
• Aggregated markers from every POV merged onto the unified timeline.
• Integrated UI — per-replay checkboxes in Flashback's Select Replay screen, no command typing required (1.21.x).
• Atomic rollback — writes to a .part file and atomically renames on success, so a failed merge never destroys your existing replays.
• Bounded memory — chat dedup is LRU-capped, chunk dedup uses cryptographic hashing, no unbounded growth on long sessions.
• i18n — French and English.

Telemetry & privacy

MultiView sends anonymous usage statistics via PostHog (EU servers) to help improve the mod. It is enabled by default but fully optional.

What is collected: mod/Minecraft/Flashback versions, OS and Java version, locale, which features are used, merge counts/durations/sizes/outcomes, and sanitized error reports.

What is never collected: player names or UUIDs, world/server names, file paths (only file names/sizes), or any replay contents. An anonymous random ID is used — it is not linked to your Minecraft account.

How to disable:

• In game: /mv telemetry off (and /mv telemetry status to check).
• Or set the JVM flag -Dmultiview.telemetry=false.
• Telemetry is automatically disabled in Fabric development environments.

Known limitations

• Secondary POVs are entities, not cameras. Flashback only supports one local player, so the camera follows the POV that started recording first ("primary"); the other recorders are visible as regular player entities.
• 4+ POV merges may show minor visual artefacts in zones where several POVs hold conflicting chunk versions.
• See SPEC.md for the full technical limitations list.

Build from source

# Default branch — Minecraft 1.21.11
./gradlew build

The jar lands in build/libs/.

Multi-version builds use a templating script:

./scripts/build-version.sh 1.21.9
./scripts/build-version.sh 1.21.11
./scripts/build-version.sh 26.1     # requires JDK 25

Development client

./gradlew runClient

Local development with Flashback:

1. Download Flashback-<ver>-for-MC<mc>.jar from Modrinth.
2. Drop it into libs/ (compile-time) and run/mods/ (runtime). Both folders are git-ignored — never commit the Flashback jar.
3. On 1.21.11 with Yarn +build.4, apply the lattice mixin patch documented in SPEC.md §10.

Documentation

• CHANGELOG.md — release history.
• SPEC.md — full spec, design journal, technical debt list.
• docs/superpowers/specs/ — per-phase design documents.
• docs/superpowers/plans/ — per-phase implementation plans.

Contributing

Issues and pull requests are welcome on GitHub. Please attach the affected MC version and a short reproduction (or sample replay folder when possible).

License

MIT — Zeffut, 2026.

Flashback remains under its proprietary license by Moulberry. MultiView is a fully independent addon and does not redistribute any Flashback code.