What is CSAI?

In a CSAI setup, the video player requests the main video file from the CDN. Simultaneously, it sends a request to an ad server for ad data, usually in VAST format. The ad server responds with a list of ads, including their URLs and durations. The player then downloads the ad media files and stitches them into the playback timeline locally.

The mechanism relies on the player's ability to switch sources quickly. When the content reaches a break point, the player pauses the main video, loads the ad file, plays it, and then resumes the main video. This process happens entirely on the user's device. The server only serves the base video and the ad metadata; it does not mix the two streams.

This approach requires the player to have reliable logic for handling network errors, buffering, and timing. If the ad file fails to load, the player must decide whether to skip the ad or retry. This complexity lives in the client code, not the backend infrastructure.

CSAI is often the default choice for smaller platforms or those with limited backend resources. It reduces the complexity of the video delivery layer because the server does not need to generate dynamic manifests for every user. You do not need to manage ad stitching logic on the server side.

However, the trade-off is significant. Because the ad data is fetched by the player, it is visible to ad blockers. This can lead to lost revenue if users block the ad requests. Also, the user experience can suffer if the network is slow, as the player must download the ad file before it can play. This can cause buffering delays at ad breaks.

For operators, CSAI is a viable option for low-volume streams or when ad revenue is a secondary goal. It simplifies the technical stack but introduces risks related to ad blocking and playback consistency. You must monitor player logs to understand how often ad requests fail or are blocked.

The core difference is where the ad stitching happens. In CSAI, the player does the work. In SSAI, the server does the work. SSAI generates a single manifest that includes both content and ads, making it invisible to ad blockers. CSAI sends separate requests for content and ads, which can be intercepted.

Consider the following comparison when choosing between the two:

• Ignoring ad blocking: Assuming all ad requests will succeed leads to underreported revenue.
• Poor error handling: If an ad file fails to load, the player may freeze or skip the break unexpectedly.
• Inconsistent timing: Network variability causes ad breaks to start late or early, confusing viewers.
• Overlooking player compatibility: Not all players handle VAST parsing equally well, leading to bugs on specific devices.
• Neglecting analytics: Without proper logging, you cannot distinguish between a blocked ad and a failed request.