PromptSync Video Compare (genkai)

Video generation is slow enough that you generate a handful of takes and then have to judge them. Watch them in two browser tabs and you will absolutely fool yourself - the second one always looks more cinematic than the first, and by the time you've switched back you've forgotten what the motion did.

PromptSync Video Compare puts both clips in one panel, synchronised, with the timed prompt beside them. It's the review step, and it's the one piece of this ecosystem's tooling that people don't realise they want until they've used it once.

How it works

Two modes, switched without losing your position:

• Stacked A / B - the videos play one above the other.
• Wipe A / B - they overlay, with a vertical divider you drag left and right to compare the same region in both takes.

Playback, pause, seeking, scene markers and looping control both videos together on a shared timeline with drift correction. Worth being precise about what that is: this is synchronised playback, not a frame-by-frame difference export. If you want pixel deltas, you don't want this node. Both videos keep their aspect ratio; if their proportions differ you'll get black bars. If they differ in length, the shorter one holds its last frame until the longer one finishes - genuinely the right behaviour, and better than the alternative where it just stops and the comparison quietly breaks.

The prompt panel is optional. With a nonempty prompt from the loader it shows your original text on the right, highlighting the current timed scene with optional auto-scroll, all in the same four reading styles plus the Obsidian theme the PromptSync viewers use. With an empty prompt it hides and the videos take the full width - which is what you want for a straight A/B.

Audio gets proper treatment: separate AUDIO A and AUDIO B waveform lanes under the shared timeline, click or drag either one to seek both, playheads following playback. Each track is toggled and levelled independently, and both start disabled at 25% volume. Mixing two soundtracks at once is rarely helpful, so muting-by-default is the sane choice. Waveforms stay visible when muted, and a clip with no audio stream is labelled rather than left blank.

Server-side, the loader probes durations and audio presence with PyAV, and the compare node renders from those local file descriptors.

The inputs and outputs that matter

One input: videos, type GENKAI_VIDEO_PAIR, required. It comes from Video Compare Loader - that's the only thing that produces the type. Connect something else and you get Connect Video Compare Loader to the videos input.

No outputs. It's a terminal, output-node-type review node. That's not a limitation you can work around, and there's no need to: the comparison is a decision step, not a data step.

How to install it

cd ComfyUI/custom_nodes
git clone https://github.com/GENKAIx/Genkai-ComfyUI-Nodes

Or ComfyUI Manager → Genkai-ComfyUI-Nodes. Restart, Ctrl+F5 - this one is a full JS panel and a stale browser cache is the most common "it's broken" report. Category: GENKAI → Video.

No models. VideoHelperSuite is not required for this pair - it's only needed by the PromptSync + Save node. The loader's example workflow ships empty and pre-wired.

Common issues

A video won't play. Use browser-compatible files: MP4 with H.264 video and AAC audio. The loader doesn't transcode incompatible uploads, so an exotic codec will load and then refuse to play.

One panel is silent and I can't fix it. Enable the track under Audio tracks - both start muted by design. If the lane says No audio track, the file genuinely has none.

Reopening the workflow gives me empty players. The files are references. They have to still exist on the ComfyUI machine, in the same place, or the panel has nothing to show.

Nothing happens when I run the workflow. Correct - press Play in the panel. Running the graph only refreshes the data; the comparison itself is manual playback, and it uses a shared timeline with drift correction rather than exporting a comparison video.