Ask LTX or Grok to continue a keeper, not a clip you still dislike
extend_video generates new frames after the last moment. Continuing a miss, or extending before picture lock, pays per second of a sequel you will not cut.
extend_video is not slow-motion. It generates new footage that continues from the last frame of an existing clip. Real rows include LTX 2.3 Extend Video (10 credits per second of output) and Grok Imagine Extend (8 credits). Pricing and available models vary; estimate_cost before you run. Motion, lighting, and identity can drift, more so the longer you push. That is an expensive way to discover you did not like the parent.
Extend a video's length is the job. The AI video generator made the parent, or you uploaded it. Extension is a sequel. Sequels need a film you would recut.
Native length is a taste pass. Extension is delivery.
Short models end when they end. If the take is wrong at second two, five more generated seconds will be the same wrong, plus drift. Watch the native clip. If it is the keeper and it is short, then extend, with a prompt that matches the existing motion.
People extend first because the platform wanted 15 seconds and the model gave 6. That math is real for a signed shot. It is not a reason to extend every sample to 15 "so we can review in context." Review 6. Extending a bin is a per-second tax.
Drift is why you do not chain three extensions on a maybe hoping the third will "find" the product. You will get a tour of a room that no longer contains the SKU.
Order
- Approve the native take.
- Choose a model on purpose (LTX vs Grok is a real cost difference).
- Extend by the shortfall you actually need, not a round number.
- Then trim, caption, mix on the continued keeper. Timed anything from before the extend is now early.
Do not caption the 6-second parent then extend. Cues will not cover the new tail, and the old cues may no longer match motion.
FAQ
Can I extend a clip I already cropped to 9:16?
You can. You should extend the master you will keep, then crop the child if needed. Extending a crop of a miss is a sequel of a crop of a ghost.
Is this how I add a second scene?
No. This continues the same shot. A second scene is another generate, assembled later with merge_movie_scenes or edit_video on keepers.
Why did lighting drift?
Because the continuation is generated, not a camera roll. Shorter extensions on a parent you like drift less. Long extensions on a parent you dislike drift and still fail.
Should I upscale before extending?
Upscale the file you will deliver, after you like the continuation. Upscaling a 6-second miss then extending it is two enhance meters on a take you will replace. Video upscale has its own lock rule.