Seedance 2.5 Decides Edit or Extend From Your Prompt

Seedance 2.5 works out which job you are giving it — a new shot, an edit, or an extension — from the clip and the prompt that arrive together. ByteDance's developer documentation puts it plainly: the model "determines the task type based on the input assets and prompt intent." 1

The jobs do not carry the same rules. An edit gives you nothing to choose: the request has to set the ratio to adaptive and the duration to -1, so the output keeps the source clip's aspect ratio and its exact length, and the reference video it works from has to run 4 to 30 seconds. 1 An extension keeps the source aspect ratio but lets you set how many seconds are added. 2

So name the job before you generate. Stating the task type moves validation earlier, so a mismatched setup is rejected at submission instead of after a generation that has already run. 1 The same switch sits in the platform interfaces as a task-type control, next to the reference inputs. 2