VQ Metrics Logger (JSON)

Run enough quality checks and you'll end up with a pile of disconnected floats and no way to compare Monday's run against Friday's. This node is the tidy-up step: it collects your metrics into one structured JSON blob you can save, diff, or feed into analysis later. It doesn't measure anything itself - it's the plumbing, and plumbing nodes are underrated.

You reach for it once you've wired up a few of the pack's scoring nodes (PSNR/SSIM, warping, FVD, whatever you're tracking) and want the results in one place instead of scattered across summary strings. Wire its JSON output to a save-text node and you've got a run log.

How it works

Nothing clever under the hood - and that's fine. It takes whatever metric floats you hand it and assembles them into a JSON object organized by category: fidelity (psnr, ssim, ciede2000), temporal (warping_error, flickering_score, smoothness_score), and distributional (fvd, fid), tagged with a name. Zero values get filtered out, so unconnected inputs don't clutter the output. That's the one behavior to know: default zeros are silently dropped, meaning a metric you forgot to wire won't appear in the JSON at all.

Inputs and outputs

Required:

• metric_name (STRING, default "video_quality") - the tag for this run. Set it to something like upscale_v2_denoise0.4 so you can tell logs apart later.

Optional (all FLOAT, all default 0, dropped when zero):

• psnr, ssim, ciede2000 - full-reference results
• warping_error, flickering_score, smoothness_score - temporal results
• fvd, fid - distributional results

Output:

• json_output (STRING) - the assembled, indented JSON.

Installing

It's one node in ComfyUI-VideoQuality-Metrics:

cd ComfyUI/custom_nodes
git clone https://github.com/jajos12/ComfyUI-VideoQuality-Metrics
pip install -r ComfyUI-VideoQuality-Metrics/requirements.txt

Restart ComfyUI; it's under VideoQuality/Reporting. ComfyUI Manager handles the pack install too.

Common issues

• Metrics missing from the JSON. You forgot to wire them, and the default zero got filtered. Check your connections - a missing key in the output means an unwired input, not a bug.
• The JSON is nested, not flat. This matters if you feed it into the pack's own comparison node, which expects flat key→number JSON. The logger's output and the comparison node don't chain cleanly - if that's your goal, either flatten manually or log the values separately. (See the VQ Workflow Comparison article for the gory details.)
• Nothing is persisted automatically. "Logger" is a slight oversell - it produces a string. Saving it to disk is on you, via a text-save or Python node.