How do I decrease the space between cards in a CardView within a RecyclerView?

Edit these attributes

card_view:cardMaxElevation="1dp"
card_view:cardElevation="1dp"

so full code will be

<?xml version="1.0" encoding="utf-8"?>

<android.support.v7.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:id="@+id/card_view"
    android:layout_width="match_parent"
    android:layout_height="200dp"
    card_view:cardCornerRadius="5dp"
    card_view:cardMaxElevation="1dp"
    card_view:cardElevation="1dp"
      card_view:cardBackgroundColor="@color/colorPrimary"
    card_view:cardUseCompatPadding="true"
    card_view:cardPreventCornerOverlap="false"
    >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:id="@+id/card_list">
        <ImageView
            android:id="@+id/thumbnail"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:gravity="center"
            android:src="@drawable/bag"
            android:contentDescription="string/video_thumbnail_description"
            android:layout_weight="1"
            />

        <TextView
            android:id="@+id/video_title_view"
            android:layout_height="match_parent"
            android:layout_width="wrap_content"
            android:layout_gravity="center"
            android:gravity="center"
            android:text="lovelksdjslkdjlsdj"
            android:layout_weight="3"
            />
    </LinearLayout>
</android.support.v7.widget.CardView>

I experiment a little bit with this, and for me...

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView
    android:id="@+id/card_view"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:cardCornerRadius="4dp"
    app:cardElevation="1dp"
    app:cardMaxElevation="1dp"
    app:cardUseCompatPadding="true" >  //this line is game changer

Happy codding