Animação do background

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/skyline"
    tools:context=".MainActivity" >

    <RelativeLayout
        android:id="@+id/relativeFundo"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="40dp" >

        <ImageView
            android:id="@+id/img_fundo"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:scaleType="fitXY"
            android:src="@drawable/fundo1" />

        <ImageView
            android:id="@+id/img_fundo2"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:scaleType="fitXY"
            android:src="@drawable/fundo1" />

        <ImageView
            android:id="@+id/img_meio"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:scaleType="fitXY"
            android:src="@drawable/meio1" />

        <ImageView
            android:id="@+id/img_meio2"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:scaleType="fitXY"
            android:src="@drawable/meio1" />

        <ImageView
            android:id="@+id/img_frente"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:scaleType="fitXY"
            android:src="@drawable/frente1" />

        <ImageView
            android:id="@+id/img_frente2"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:scaleType="fitXY"
            android:src="@drawable/frente1" />
    </RelativeLayout>

  
</RelativeLayout>

Animação.java

import android.view.animation.LinearInterpolator;
import android.view.animation.TranslateAnimation;
import android.widget.ImageView;

public class Animacao {
	public static Integer ANIM_INICIO = 0;
	public static Integer ANIM_FIM = 1;
	public static Integer FRENTE = 1;
	public static Integer MEIO = 2;
	public static Integer FUNDO = 3;
	
	public static void animFundo(ImageView imagem, Integer animacao, Integer nivel, Integer width){
		if (imagem == null){
			return;
		}

		TranslateAnimation anim; 
		if (animacao.equals(ANIM_INICIO)){
			anim = new TranslateAnimation(0.0f, -width, 0.0f, 0.0f);
		} else if (animacao.equals(ANIM_FIM)){
			anim = new TranslateAnimation(width, 0.0f, 0.0f, 0.0f);
		} else {
			return;
		}
		
		switch (nivel) {
		case 1:
			anim.setDuration(10000);
			break;
		case 2:
			anim.setDuration(30000);
			break;
		case 3:
			anim.setDuration(100000);
			break;

		default:
			return;
		}
		
		anim.setRepeatCount(TranslateAnimation.INFINITE); 
		anim.setRepeatMode(1); 
		anim.setFillAfter(false);
		anim.setFillBefore(false);
		anim.setInterpolator(new LinearInterpolator());
		
		imagem.startAnimation(anim);
	}

}

MainActivity.java

import android.app.Activity;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.Menu;
import android.widget.ImageView;

public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		animacaoFundo();
	}
	
	
	private void animacaoFundo() {
	
	DisplayMetrics displayMetrics = new DisplayMetrics();
	
	getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
	int width = displayMetrics.widthPixels;

	Animacao.animFundo(findImg(R.id.img_frente), Animacao.ANIM_INICIO, Animacao.FRENTE, width);
	Animacao.animFundo(findImg(R.id.img_frente2), Animacao.ANIM_FIM, Animacao.FRENTE, width);

	Animacao.animFundo(findImg(R.id.img_meio), Animacao.ANIM_INICIO, Animacao.MEIO, width);
	Animacao.animFundo(findImg(R.id.img_meio2), Animacao.ANIM_FIM, Animacao.MEIO, width);

	Animacao.animFundo(findImg(R.id.img_fundo), Animacao.ANIM_INICIO, Animacao.FUNDO, width);
	Animacao.animFundo(findImg(R.id.img_fundo2), Animacao.ANIM_FIM, Animacao.FUNDO, width);
	}
	
	private ImageView findImg(int id){
		return (ImageView) findViewById(id);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

}