# MediaTailor HLS and DASH explicit session initialization
<a name="manifest-query-parameters-hls-and-dash-explicit-session-initialization"></a>

AWS Elemental MediaTailor includes the `manifestParams` as query parameters in the multivariant playlist and tracking URLs in the response when the client makes an explicit session initialization request.

**Session initialization methods**  
For explicit session initialization, you can use either POST with request body or GET with query parameters:

1. **POST with Request Body:**

   ```
   POST /v1/session/{{111122223333}}/{{originId}}/index.m3u8
   {
       "adsParams": {"param1": "value1", "param2": "value2", "param3": "value3"},
       "manifestParams": {"test": "123"}
   }
   ```

1. **GET with Query Parameters:**

   ```
   GET /v1/session/{{111122223333}}/{{originId}}/index.m3u8?ads.param1=value1&ads.param2=value2&manifestParams.test=123
   ```

**Example session initialization request**  

```
POST /v1/session/{{{{111122223333}}}}/{{originId}}/index.m3u8
{
    "adsParams": {
        "param1": "value1",
        "param2": "value2",
        "param3": "value3"
    },
    "manifestParams": { 
        "test": "123"
    },
    "reportingMode": "client"
}
```

**Example manifest and tracking response**  

```
{
    "manifestUrl": "/v1/master/{{{{111122223333}}}}/{{originId}}/index.m3u8?aws.sessionId={{session}}&test=123",
    "trackingUrl": "/v1/tracking/{{{{111122223333}}}}/{{originId}}/{{session}}?test=123"
}
```

Manifest responses for the session have the specific `manifestParams` in MediaTailor URLs similar to the previously described implicit session-initialization workflows. The key difference is that manifest parameters for explicit session initialization don't start with `manifest.`.

Manifest query parameters are immutable and you can only set them on session initialization. If a client makes multiple multivariant playlist requests for a single session, MediaTailor doesn't update the manifest query parameters after the first request.

**Parameter processing flow**  
You can only specify parameters once, at initialization time. Configuration aliases resolve to actual values before forwarding. For example: `player_params.ad_type=customized` resolves to `ad_type=abc12345` based on the ConfigurationAliases configuration.