# MediaTailor player variables for ADS requests
<a name="variables-player"></a>

AWS Elemental MediaTailor sends data received from the player to the ADS when you configure AWS Elemental MediaTailor to specify `player_params.<query_parameter_name>` variables in the template ADS URL. For example, if the player sends a query parameter named `user_id` in its request to MediaTailor, to pass that data in the ADS request, include `[player_params.user_id]` in the ADS URL configuration. 

This allows you to control the query parameters that are included in the ADS request. Typically, you add a special query parameter that the ADS recognizes to the ADS request URL and provide key-value pairs as the value of the parameter. 

The examples used in the following procedure use the following key-value pairs:
+ *param1* with a value of *value1:*
+ *param2* with a value of *value2:*

**To add query parameters as key-value pairs** 

1. In AWS Elemental MediaTailor, configure the ADS request template URL to reference the parameters. The following URL shows the inclusion of the example parameters: 

   ```
   https://my.ads.com/path?param1=[player_params.param1]&param2=[player_params.param2]
   ```

1. (Optional) For server-side ad-tracking reporting, URL-encode the key-value pairs on the player. When MediaTailor receives the session initialization request, it URL-decodes the values once before substituting them into the ADS request URL. 
**Note**  
If your ADS requires a URL-encoded value, URL-encode the value twice on the player. This way, the decoding done by MediaTailor results in a once-encoded value for the ADS. 

   For example, if the decoded representation of the values sent to the ADS is `param1=value1:&param2=value2:`, then the URL-encoded representation is `param1=value1%3A&param2=value2%3A`.

1. In the session initialization call from the player, pass the key-value pairs to MediaTailor as the value of a single query parameter. The following example calls provide the example key-value pairs for server- and client-side ad tracking reporting.
   + Example requests for server-side ad-tracking reporting - using URL-encoded pairs

     HLS:

     ```
     <master>.m3u8?ads.param1=value1%3A&ads.param2=value2%3A
     ```

     DASH:

     ```
     <manifest>.mpd?ads.param1=value1%3A&ads.param2=value2%3A
     ```
   + Example request for client-side ad-tracking reporting - with no URL-encoding

     HLS:

     ```
     POST <master>.m3u8
         {
             "adsParams": {
                "param1": "value1:",
                "param2": "value2:"
            }
         }
     ```

     DASH:

     ```
     POST <manifest>.mpd
         {
             "adsParams": {
                "param1": "value1:",
                "param2": "value2:"
            }
         }
     ```

For server-side reporting, MediaTailor decodes the parameters when the player request is received. For client-side reporting, it doesn't alter the parameters received in the JSON payload. MediaTailor sends the following request to the ADS:

```
https://my.ads.com/<path>?param1=value1:&param2=value2:
```

In this way, the `param1` and `param2` key-value pairs are included as first-class query parameters in the ADS request.