Asset Filters

Asset filters allow for just-in-time filtering of the contents of a video manifest. This is useful, for instance, when you want to present specific language tracks to a user based on their language preferences, or when you need to suppress certain tracks from being presented to devices that lack support, or when you want to present a specific bitrate to users when a stream starts.

Asset filters are applied to a specific asset, and are evaluated at the time of playback. They are not applied to the underlying asset itself, and multiple filters can be applied to a single asset. Filters are applied in the order they are created, with multiple filters being OR'd together to produce the final result.

Filters have several important capabilities:

1. Initial bitrate selection. In an HLS playlist, this feature determines the order of the tracks in the playlist, which determines where the client starts playback. Adjust this value in order to tune the initial playback experience for your users.
2. VOD time window filtering. This is a capability that permits for a time window to be applied for a VOD asset's presentation. Consider a scenario where you have a 24-hour asset comprised of 24 back-to-back one-hour programs. You might create 24 separate asset filters and 24 separate streaming locators in order to present 24 unique programs to your users. Why you would prefer this approach over simply creating 24 separate assets is an exercise left to the reader.
3. Live window delays (liveWindowBackoff). You can delay playback behind the "live point", for instance to allow for a delay in the presentation of a live event. This is useful in cases where you have a global cache that you would like to preheat. Clients view the delayed presentation, while the cache is populated with the live presentation.
4. Live Sliding Window duration. This is setting the window of time between the live point of a manifest and the last video segment in a manifest. A live manifest, especially for long-duration content, can impair startup times. A common use case is to construct two live manifests, one with a short window for fast startup and playback at the live point, and another with a longer window for users who want to watch the entire event.
5. Track filtering. Actually this is track inclusion. Define predicates that describe your video content and any matching tracks will be included in the manifest. Use this feature to create differentiated manifests based on client capabilities, or languages, or any other criteria you can think of.

Asset filters and account filters are exactly the same. Asset filters differ from account filters in that they are only assignable to a specific asset, though the interface is identical. Prefer asset filters in cases where your content is unique - typically VOD content time window filtering. In cases where you want a common set of rules applied across all your content, use an account filter.