Gemini Omni extension only appends: how to add a lead-in clip

Can Gemini Omni extend a video backwards, or insert a scene in the middle? No. The Gemini API Omni docs say extension appends to the end only, with no prepend and no middle insert, and that uploaded input videos must be 10 seconds or shorter. To get a lead-in before existing footage, create the lead-in as its own clip and join the two.

What Google documents

Google's launch post says scene extension analyzes up to 10 seconds of prior context and extends in 10 second increments up to 40 seconds. That is a forward-only chain.

The Sume route

Sume's gemini-omni-flash-1.1 row does not expose extend or previous_interaction_id; its edit mode takes a video_url. So the lead-in plan is an assembly plan, not an extension.

• Pull the first frame of your footage with video-frames using at[].
• Generate the lead-in with that frame as the last-frame input, so the lead-in ends on a frame that matches your footage.
• Join the lead-in and your clip on a timeline render.

Limits to plan for

Sume lists Omni at 3 to 10 seconds, 16:9 and 9:16 only, so the lead-in must match the aspect ratio of the footage. The first-frame match will not hide a change in lighting or motion, so keep the lead-in short and expect a visible cut. Generate two or three candidates and choose the one whose last frame sits closest to the footage.

A note on what Sume does not do

Sume does not run Veo or any model absent from its video catalog, and it does not expose Google's extend feature for Omni. If your workflow depends on the Gemini app's scene extension, that runs in Google's own products: Flow for AI Plus, Pro and Ultra subscribers, and the Gemini app, according to the launch post.

Sequence to run

Work backward from the footage you already have. First decide how long the lead-in should be; Omni on Sume produces 3 to 10 seconds, so a 6 second lead-in leaves room for a retake. Second, extract the frame the lead-in must land on. Third, write the prompt as a description of the motion that ends in that frame, not of the frame itself. Fourth, render the join on the timeline and watch the seam at full speed rather than frame by frame, because a seam that looks clean when paused can still pop in motion.