Speed ramp
Watch as an animation →Go fast, then slow down at the key moment (or the other way round), making that moment dramatic.
The moment a product drops, sports and action, the moment a door opens.
Stretching a slow section afterward makes it choppy, so generate it with "slow motion" in the prompt. Speed up the sections before and after with setpts=0.5*PTS. AI clips often come out slow, so playing them 1.2 to 1.5 times faster often looks natural.
Ramp a 4-second clip: the first 2 seconds at double speed, then the last 2 seconds in half-speed slow motion: ffmpeg -i in.mp4 -filter_complex "[0:v]trim=0:2,setpts=0.5*(PTS-STARTPTS)[a];[0:v]trim=2:4,setpts=2*(PTS-STARTPTS)[b];[a][b]concat=n=2:v=1:a=0" out.mp4. Put "slow motion" in the generation prompt so the slow part stays smooth.
Techlude — AI Cinematic Product Ad Using Kling 3.0 (Higgsfield): Speed Ramp