# Write and examine the code
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In this section of the [Java producer library procedure](https://docs.aws.amazon.com/kinesisvideostreams/latest/dg/producer-sdk-javaapi.html), you write and examine the Java example code that you downloaded in the previous section. 

The Java test application ([https://github.com/awslabs/amazon-kinesis-video-streams-producer-sdk-java/blob/master/src/main/demo/com/amazonaws/kinesisvideo/demoapp/DemoAppMain.java](https://github.com/awslabs/amazon-kinesis-video-streams-producer-sdk-java/blob/master/src/main/demo/com/amazonaws/kinesisvideo/demoapp/DemoAppMain.java)) shows the following coding pattern:
+ Create an instance of `KinesisVideoClient`.
+ Create an instance of `MediaSource`.
+ Register the `MediaSource` with the client.
+ Start streaming. Start the `MediaSource` and it starts sending data to the client.

The following sections provide details.



## Create an instance of KinesisVideoClient
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You create the `KinesisVideoClient` object by calling the `createKinesisVideoClient` operation.

```
final KinesisVideoClient kinesisVideoClient = KinesisVideoJavaClientFactory
    .createKinesisVideoClient(
        Regions.US_WEST_2,
        AuthHelper.getSystemPropertiesCredentialsProvider());
```

For `KinesisVideoClient` to make network calls, it needs credentials to authenticate. You pass in an instance of `SystemPropertiesCredentialsProvider`, which reads `AWSCredentials` for the default profile in the credentials file:

```
[default]
aws_access_key_id = ABCDEFGHIJKLMOPQRSTU
aws_secret_access_key = AbCd1234EfGh5678IjKl9012MnOp3456QrSt7890
```





## Create an instance of MediaSource
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To send bytes to your Kinesis video stream, you must produce the data. Amazon Kinesis Video Streams provides the `MediaSource` interface, which represents the data source.

For example, the Kinesis Video Streams Java library provides the `ImageFileMediaSource` implementation of the `MediaSource` interface. This class only reads data from a series of media files rather than a Kinesis video stream, but you can use it for testing the code.

```
final MediaSource bytesMediaSource = createImageFileMediaSource();
```

## Register the MediaSource with the client
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Register the media source that you created with the `KinesisVideoClient` so that it knows about the client (and can then send data to the client).

```
kinesisVideoClient.registerMediaSource(mediaSource);
```



## Start the media source
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Start the media source so that it can begin generating data and send it to the client.

```
bytesMediaSource.start();
```