arkennemasis fal · Flux 3 Keyframes to Video Draft · $0.06/s

Keyframe shots fail in a specific, boring way: the anchors are fine, the pacing isn't. You put the turn at frame 40 and it should have been frame 60, so the model rushes it and you get a smear. That's a timing problem, and timing is the one thing you can absolutely judge from a low-quality preview - which makes drafting not just cheaper but genuinely more useful here than for a simple text-to-video shot.

ArkFal_blackforestlabs_flux_3_keyframes_to_video_draft renders the same keyframe shot at $0.06 per second and returns a reusable draft cache for draft_enhance to finish at full quality.

What you set

• keyframes - required, a JSON list of {image_url, frame_index} objects, up to 10, with unique frame indices. Pre-filled with fal's own example so you can see the shape. You paste image URLs here; these are not IMAGE sockets.
• duration - whole seconds, 5 through 20, default 5. An explicit duration is required: the model has to validate where each keyframe lands against the length of the clip.
• prompt - what happens between the anchors.
• generate_audio - on by default. Draft audio is included at no extra cost.
• aspect_ratio - auto by default.
• safety_tolerance - 0 strictest, 4 most permissive, default 2.

No resolution. Drafts are 720p-class; that's the price you're paying less for.

Optional shared controls: max_cost_usd (default $20 cap, checked before upload - nothing gets sent if the estimate is higher), reuse_identical_run (on by default), extra_json, max_concurrent.

Outputs: video, video_path, draft_cache_path, info.

Moving the cache to the finisher

Here's the thing that catches literally everyone on their first try: the draft saves the encrypted bundle locally as draft_cache_path, and the enhance node wants draft_cache_url - a URL or data URI - which it hands to fal untouched. Local paths don't travel. The bundle's fal URL is in the draft's info output (fal's full answer, including the draft_cache file object) and it's also written to output/fal/_requests.jsonl. Paste it from there.

Keep it. A draft cache is the difference between paying for a preview and paying for a preview plus a render.

Install

cd ComfyUI/custom_nodes
git clone https://github.com/Hishamahmer/comfyui-arkennemasis

Restart ComfyUI (or install via Manager - search arkennemasis), then put the key in the .env:

FAL_KEY=your-key-from-fal.ai/dashboard/keys

The file goes next to run_nvidia_gpu.bat on a portable install, or in the ComfyUI folder otherwise. There's no key input on the node on purpose, so no workflow file can leak one. Nothing to download, either - FLUX 3 is API-only access, which is exactly why this pack wraps it rather than shipping weights.

Worth knowing

Budget your keyframes as a sequence, not individually. Placing an anchor at index 0, one at 60 and one at 140 in a 6-second clip is asking the model to interpolate two moves in a hurry; the draft is how you find that out for $0.36 instead of $1.74.

Results land in output/fal/blackforestlabs_flux-3_keyframes-to-video_draft/ and the node previews the clip on itself. Rate limits and dropped connections are retried with backoff automatically, Cancel cancels the render on fal's side, and a run interrupted by a restart is recoverable for free by request id.