Sam 2 (https://sam2.metademolab.com – “Segment anything”, Meta demo) spots and tracks up to 3 objects/shapes on a video and allows you to modify them or change what’s around it.
Videos up to 70MB. Without an account and unlimited.

Tests from Pexels free videos:

• https://sam2.metademolab.com/shared/39c981c3-a1da-49ef-a19c-c5be772ab51c.mp4 (source:
  https://www.pexels.com/fr-fr/video/ville-homme-gens-rue-18812173/)
• https://sam2.metademolab.com/shared/b235fffc-426b-4123-9d77-3a426886af2d.mp4 (source: https://www.pexels.com/fr-fr/video/autoroute-urbaine-tres-frequentee-avec-un-trafic-fluide-29607724/)
• https://sam2.metademolab.com/shared/1fef26ec-9a44-4c07-aab4-b99e8bb49505.mp4 (source: https://www.pexels.com/fr-fr/video/ciel-voler-oiseaux-aviaire-9126818/)