Upload And Extend Audio · V5.5

Here's the difference between this node and its sibling Extend Music, in one line: Extend takes a Suno audio_id, this one takes an upload_url. If your source is a file you already own - a loop you made, a stem, an old render, something from a local model - this is the node, because KIE can fetch a URL and it can't fetch your hard drive.

The job is the same: pick a point in the track and let the model continue from there. Useful when a 20-second generate comes back and you want a 90-second version, or when a locally generated loop needs a middle section before you cut it into a video.

How it works

The pack builds its node classes from KIE's official API documentation on startup, one node per documented model version - so this class is fixed to V5_5 with no dropdown to change. The node builds the documented request body, submits it to KIE's task endpoint (envelope model ai-music-api/upload-and-extend, inner model V5_5), then polls KIE's record-info endpoint every couple of seconds with exponential backoff until the task completes. On success it downloads the mp3 and returns a native ComfyUI AUDIO; on failure it raises with the task id and the provider's message.

The inputs that matter

• upload_url (required) - the source, as a public URL. The docs cap upload-based source audio at 8 minutes and say the source alone is enough to generate.
• prompt - used as lyrics only if lyrics is empty, and it must not be set when instrumental is true.
• continue_at - the field that actually matters. Seconds, default 60, and per the docs it must be greater than 0 and less than the total duration of the uploaded audio. Get this wrong in either direction and the request fails.
• instrumental - defaults to true, which is worth noticing, because it means a lyrics prompt is ignored unless you flip it. That default is the opposite of the Extend node's.

The rest is steering: style (align it with the source; it's up to 1000 characters on this tier), title, negative_tags, vocal_gender, style_weight, weirdness_constraint, audio_weight, persona_id / persona_model, lyrics, variety (0–4), plus timeout_seconds (1200) and callback_url (leave empty).

Outputs: audio, url, all_urls_json, task_id, raw_json, credits_consumed, credits_left. When you extend an upload, the response carries both source and generated URLs - all_urls_json is where you keep them, and task_id plus url make cheap logging if you're iterating on continue_at.

Feeding it a local file

upload_url is a text box, not an AUDIO socket, so wire it: drop KIE • Upload Audio (in KIE Next/Utility/Media), connect your AUDIO to it, then right-click upload_url on this node, choose Convert widget to input, and connect the URL string. Once that's in place you can run a fully local-generate → upload → extend chain without touching a URL by hand.

Installing

ComfyUI Manager, search "KIE Nodes Next"; the README still frames registry publication as prepared rather than live, so the clone path is what actually works when Manager comes up empty:

cd ComfyUI/custom_nodes
git clone https://github.com/felipederosilva/ComfyUI-KIE-Nodes-Next
pip install -r ComfyUI-KIE-Nodes-Next/requirements.txt

Restart, then set the key once at Settings → KIE.ai Nodes Next → Connection. It's validated before replacing a working key, and nothing but a masked fingerprint reaches the UI. KIE_API_KEY in the environment overrides the saved key if you're running headless. Dependencies are four small libraries - no torch, no model files, no VRAM cost.

Where people get burned

• continue_at outside the source's length is the most common failure. Check the actual duration first; a value of 60 on a 45-second file can't work.
• Instrumental defaults. If you set prompt and got an instrumental back, that's why - instrumental shipped true.
• No key throws an explicit error with the settings path in it. Always check that before debugging anything else.
• A timeout isn't a cancellation. The node stops polling at timeout_seconds; the remote task can still finish. Look at credits_consumed before rerunning.
• Mixed installs are refused on startup. If the pack complains that its version and the generated-node build disagree, delete the ComfyUI-KIE-Nodes-Next folder and reinstall.
• V5.5 sits in the discontinued tier per KIE's docs. New work should use the V6 sibling; this one earns its keep reproducing existing renders.

Worth saying out loud: extension quality degrades with distance. Adding ten seconds to a track usually sounds seamless; adding two minutes tends to wander. Chain short extensions and re-check the seam each time rather than asking for one long one.