PRE_SESSION_INITIALIZATION
When it fires
MediaTailor runs the function mapped to PRE_SESSION_INITIALIZATION once,
at the start of a new playback session. The function runs before MediaTailor constructs
the initial manifest response.
Input
session.*, player_params.*, and
event.*. See the Input field reference for the complete
list.
Output namespace allowed
| Namespace | Accepted types |
|---|---|
player_params.* |
Strings, numbers, booleans |
Values written to player_params.* are persisted to the session. They
are available:
-
As input at the
PRE_ADS_REQUESTlifecycle hook viaplayer_params.* -
In ADS request URLs through MediaTailor dynamic ad variables for ADS requests (for example,
[player_params.deviceType]) -
For the lifetime of the session across all ad breaks
Note
The total serialized size of all
player_params output keys and values must not exceed 1,000 characters.
If the total exceeds this limit, the function output is discarded. For more
information, see Functions limits.
Typical use cases
-
Fetch identity or audience data from an external service and store it in player parameters for use in later ADS requests.
-
Classify the device type based on the user agent and write the classification to a player parameter.
-
Set default player parameter values that downstream ad break processing relies on.
-
Store values in player parameters that are included in the ADS URL through MediaTailor dynamic ad variables for ADS requests.
Failure behavior
If a function attached to PRE_SESSION_INITIALIZATION fails for any
reason, MediaTailor discards the function's output and proceeds as if no function were
attached. The session starts normally without the function's player parameter
values.
