WAN VACE Auto Joiner - Save

If you look at the WAN VACE Auto Joiner pack and think "that Save node is just bookkeeping," you're missing the entire reason this workflow doesn't fall apart. This is the node that makes the loop safe.

The problem it solves is timing. ComfyUI For Loops (from ComfyUI-Easy-Use) let you iterate a subgraph, but VACE generation is slow and asynchronous - the next loop iteration can fire before the previous transition is actually done. The pack's answer is a barrier: this node writes the finished VACE output to disk, and only then passes value1 through to For Loop End. The next iteration's PROCESS step reads that file back. No file on disk, no pass-through, no next step. The README is explicit about why they didn't just use FLOW_CONTROL: it doesn't block async VACE execution, so it's not a real dependency.

What to connect

Three inputs, all required, and the wiring matters:

• value1 - from For Loop Start's value1 output.
• vace_images - the IMAGE tensor out of VAE Decode after your VACE step.
• directory - the same clips folder the Auto Joiner node uses; it needs to match so it can find the temp-* state folder.

The output is the same value1, passed through unchanged, which goes into For Loop End's initial_value1 input. That pass-through is the whole trick: the loop can't close until the VACE output has actually been written. The other two outputs (status, is_complete) are debug.

Where it sits

Inside the loop, after VAE Decode:

For Loop Start ──value1──► Save ──value1──► For Loop End
                          ▲
                          └── vace_images (from VAE Decode)

If the loop finishes but the final video is missing a transition, this node is the first place to look. The telltale error is "No VACE output found. Save node must run after VACE." - meaning the Save node either ran before the decode finished or never ran at all.

Install and gotchas

Same pack, same install as the Auto Joiner node: ComfyUI Manager search for "Wan Vace Auto Joiner", or git clone https://github.com/Rhovanx/wan_vace_auto_joiner.git into ComfyUI/custom_nodes, then restart. You need ComfyUI-Easy-Use installed for the For Loop nodes, and this node writes a vace_output.pt into the temp folder inside your clips directory - keep that folder until Finalize has run and you're happy with the result, since that's where your assembled frames live between iterations. It's an output node, so it marks the loop subgraph as done when it fires - which is exactly the barrier behavior you want.

This is the least glamorous node in the pack and also the one you shouldn't skip. Skip it and you're back to joining clips by hand.