CSAI (client-side ad insertion) is the model where the player itself calls the ad server and plays ads separately from the content, switching from the content stream to an ad and back. It is the traditional web-video approach: the player runs an ad SDK (often IMA), requests a VAST/VMAP response at break points, and handles ad playback, tracking, and any interactive elements on the client.
CSAI's strengths are simplicity and rich interactivity: clickable ads, overlays, skippable formats, and detailed client-side tracking are all easier when the player controls the ad. Its weaknesses are equally clear — ad-blockers can intercept the ad calls, and switching streams causes latency or buffering at the ad boundary, which is especially rough on smart TVs and low-power devices.
In practice CSAI suits the open web and interactive campaigns, while SSAI suits TV-like, block-resistant, seamless playback. Many platforms use both, choosing per device or per placement.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
CSAI is the simplest way to put ads into video, and ad blockers and rebuffering at the ad break are where it fails. We wrote seven volumes covering the video stack; for CSAI start with Volume 3 on players, playback recovery, and streaming economics, then Volume 2 on HLS and DASH manifests, with encoding in Volume 1. Written by Nikolay Sapunov, CEO at Fora Soft.
Deciding between client-side ad insertion and SSAI for your player?
We will review your players and ad server setup and send an ad insertion plan with the tradeoffs per device. 250+ video products shipped since 2005.
