FlashbackTurbo
A Fabric addon for Flashback that drastically speeds up video export — without quality loss.
Proven in the field
Validated across hundreds of real anonymous exports on Windows (primary platform), macOS and Linux. Export failure rate ~1%, and every observed failure was external (not enough RAM allocated for very long replays, or the game closed mid-export) — never a regression introduced by FlashbackTurbo itself.
What it does
Patches Flashback's export pipeline via Mixin to replace serial, low-tuned operations with parallel ones:
- Parallel PNG writer (N-1 threads) + configurable zlib level + RGB color-type when transparency is off
- FFmpeg threading tunes per encoder (
h264_nvenc,h264_qsv,h264_videotoolbox,libopenh264) - Removes the silent 4K downscale cap
- Fragmented MP4 muxer on hardware encoders → ~10× faster finalize
- Animated "Saving…" overlay during the post-export phase
- Fixes a Flashback crash on mid-replay exports (null
mc.levelrace) - Auto-promotes software → GPU encoding (0.5.0) — when an export would use the slow
libopenh264encoder, redirects it to a hardware encoder (NVENC/QSV) when one is available, for the ~13% of exports on software-only configs. Fail-safe, SSIM ≥ 0.99. - Silent auto-update (0.6.0) — keeps your Zeffut mods up to date from Modrinth automatically: background check on launch, verified download, swap at game exit. Opt out with
"autoUpdate": falsein the config.
All hooks are opt-in via config/flashbackturbo.json and default to safe values.
Performance
Controlled benchmark (PNG sequence)
Real 1.21.11 replay, 10-second slice at 1920×1080 (603 frames):
| Mode | Total | Per frame |
|---|---|---|
| Vanilla | 96 081 ms | 159 ms |
| Turbo | 8 774 ms | 14 ms |
10.95× end-to-end.
Real-world field data (MP4 export)
Median export time across real exports (~1080p clips), by encoder:
| Platform · encoder | Median export |
|---|---|
Windows · NVIDIA h264_nvenc |
~8.5 s (60 fps) |
Windows · Intel h264_qsv |
~23 s (60 fps) |
macOS · h264_videotoolbox |
~26 s (30 fps) |
Software fallback libopenh264 |
~55 s |
Fastest on Windows + an NVIDIA GPU. A coming release auto-promotes pure-software exports to the GPU encoder when one is available.
Quality
Lossless PNG output — zlib level only changes file size, decoded pixels are bit-identical. The FFmpeg threading tunes don't change the encoded bitstream.
Privacy
Since 0.4.0, FlashbackTurbo sends anonymous usage telemetry (PostHog) to prioritise improvements: a random local UUID, no username / IP / file paths, sanitised exception messages. Fully fail-safe (it can never slow down or break an export) and opt-out — set "enableTelemetry": false in the config.
Requirements
- Flashback and Fabric API
- Minecraft 1.21.9 / 1.21.10 / 1.21.11 (Java 21) — or 26.1.x (Java 25)
