H3 MCtx Result Preview (obvpm)

Here's the workflow problem this node solves, and it's a real one. You extend an H3 clip. The take saves. You look at it in your media player - where it starts at frame zero with no idea what came before it. So you open the parent, scrub to the end, open the take, scrub to the start, and try to hold both in your head. That's a terrible way to judge whether a generation worked.

H3 MCtx Result Preview wires a single string in and shows you a mini timeline: the fresh take beside the clip it continues, played seamlessly as one, with the seam derived from the sidecars rather than guessed.

How it works

You wire a Save node's path output into path. That's the entire input surface - required, no optional inputs, no outputs. After each run, the node resolves lineage server-side (the take's sidecar says who its parent is; the parent's sidecar is found by scanning the take's folder), then builds the pair through the same smart-cut preview route the Timeline node uses.

Extend: parent first, then the take. Prepend: take first, then the clip it leads into. Either way you get one playable stream, gapless, because a single file is the only kind of preview that can actually be sample-locked - two <video> elements never can.

It also measures the join and reports how seamless it is, which is the difference between "it looked fine on my monitor at 1080p" and an actual number.

The buttons that make it worth wiring

• + add to timeline - the pack's replacement for the Timeline's old auto_add (which is now deprecated and unused). New takes are offered here instead of appearing silently.
• delete / dismiss - a take that didn't connect costs you one click to get rid of, which matters when you're re-rolling.
• Model preview override: integrated, so while the generation is still running you can watch a cheap preview of it and kill a run that's going wrong instead of waiting eight minutes to find out.

The workflow ships with two instances of this node wired up - one on the generation branch, one on the upscale/refine branch - so a rendered 4x sequence also gets the "did it connect" check.

Install

cd ComfyUI/custom_nodes
git clone https://github.com/chanon/comfyui-obvpm-timeline

Restart ComfyUI. No Python deps, no model downloads for this node itself. Needs ComfyUI 2026-08-13+ for core H3. Manager: search comfyui-obvpm-timeline. All nodes carry the (obvpm) suffix, so obvpm in the node search finds them.

Worth knowing: the preview and export endpoints are stateless utility routes. They drive no generation, hold no state and don't gate review - the node exists so you can look, not so the graph can decide.

Troubleshooting

• Blank widget after a run. The path input needs a real saved clip with a sidecar next to it. If you wired some other saver's filename out, there may be no lineage to find and nothing to show against.
• It shows the take alone. That means the lineage edge wasn't recorded - most often because the pins wire that fed H3 MCtx Apply Pins wasn't also wired to the Save node. The sidecar then records the take as a root, which is also why it can't be crossfaded later.
• Preview looks worse than the clip. It's a preview route, built by cutting and copying packets; trust the exported file, not the low-bitrate widget playback, when judging fine texture.
• Two previews fighting? Each Timeline node wants its own preview_filename, and previews are single files overwritten on every build. Don't point several things at the same name.

If you only take one habit from this pack: after every continuation run, glance at this node before you queue the next one. Chaining four clips off a take that didn't actually connect is how you lose an hour.