Quelle  activity_group_call.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/group_call_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/gallery_background"
    tools:context=".voip.activities.GroupCallActivity">

    <ImageView
        android:id="@+id/background_image"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="centerCrop"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="ContentDescription" />

    <!-- region participant list and background gradient -->
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/group_call_participants"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <View
        android:id="@+id/gradient_overlay"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/call_background_gradient"
        android:visibility="visible"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <!-- endregion participant list and background gradient -->

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/content_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <!-- region group call info -->
        <androidx.constraintlayout.widget.ConstraintLayout
            android:id="@+id/call_info"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginStart="@dimen/call_activity_margin"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent">

            <ch.threema.app.emojis.EmojiTextView
                android:id="@+id/call_title"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginTop="@dimen/grid_unit_x1"
                android:ellipsize="end"
                android:fontFamily="sans-serif-light"
                android:maxLines="1"
                android:textColor="@android:color/white"
                android:textSize="@dimen/group_call_title_text_size"
                app:layout_constraintEnd_toStartOf="@id/video_buttons_barrier"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                tools:text="Call Title" />

            <TextView
                android:id="@+id/call_sub_title"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:ellipsize="end"
                android:fontFamily="sans-serif-light"
                android:maxLines="1"
                android:textColor="#ffffff"
                android:textSize="@dimen/group_call_status_text_size"
                app:layout_constraintEnd_toStartOf="@id/video_buttons_barrier"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@id/call_title"
                tools:text="Call sub title" />


            <ch.threema.app.ui.AnimatedEllipsisTextView
                android:id="@+id/call_status"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:ellipsize="none"
                android:fontFamily="sans-serif-light"
                android:textColor="#ffffff"
                android:textSize="@dimen/group_call_status_text_size"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@id/call_sub_title" />

            <Chronometer
                android:id="@+id/call_duration"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:fontFamily="sans-serif-light"
                android:textColor="#ffffff"
                android:textSize="@dimen/call_status_text_size"
                android:visibility="gone"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@id/call_sub_title" />

            <ImageButton
                android:id="@+id/button_toggle_camera"
                android:layout_width="@dimen/call_activity_small_button_size"
                android:layout_height="@dimen/call_activity_small_button_size"
                android:layout_marginTop="@dimen/call_video_button_margin_top"
                android:background="@drawable/ripple_call_button"
                android:contentDescription="@string/voip_toggle_video"
                android:focusable="true"
                android:scaleType="center"
                android:visibility="gone"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:srcCompat="@drawable/ic_videocam_off_black_outline"
                app:tint="@android:color/white"
                tools:visibility="visible" />

            <ImageButton
                android:id="@+id/button_flip_camera"
                android:layout_width="@dimen/call_activity_small_button_size"
                android:layout_height="@dimen/call_activity_small_button_size"
                android:background="@drawable/ripple_call_button"
                android:contentDescription="@string/voip_switch_cam"
                android:focusable="true"
                android:scaleType="center"
                android:visibility="gone"
                app:layout_constraintEnd_toStartOf="@id/button_toggle_camera"
                app:layout_constraintTop_toTopOf="@id/button_toggle_camera"
                app:srcCompat="@drawable/ic_flip_camera_android"
                app:tint="@android:color/white" />

            <androidx.constraintlayout.widget.Barrier
                android:id="@+id/video_buttons_barrier"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                app:barrierDirection="left"
                app:constraint_referenced_ids="button_flip_camera,button_toggle_camera" />

        </androidx.constraintlayout.widget.ConstraintLayout>
        <!-- endregion group call info -->

        <!-- region Call Controls -->
        <androidx.constraintlayout.widget.ConstraintLayout
            android:id="@+id/in_call_buttons"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="@dimen/call_activity_margin"
            android:layout_marginBottom="@dimen/call_activity_margin"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toStartOf="parent">

            <ImageButton
                android:id="@+id/button_end_call"
                android:layout_width="@dimen/call_activity_small_button_size"
                android:layout_height="@dimen/call_activity_small_button_size"
                android:background="@drawable/ic_circle_lockscreen_red"
                android:contentDescription="@string/leave"
                android:focusable="true"
                android:foreground="@drawable/selector_avatar"
                android:scaleType="center"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:srcCompat="@drawable/ic_call_end_outline"
                app:tint="@android:color/white" />

            <ch.threema.app.voip.CallAudioSelectorButton
                android:id="@+id/button_select_audio_device"
                android:layout_width="@dimen/call_activity_small_button_size"
                android:layout_height="@dimen/call_activity_small_button_size"
                android:layout_marginLeft="16dp"
                android:background="@drawable/ic_compound_audio_source_24dp"
                android:clickable="true"
                android:contentDescription="@string/voip_toggle_speaker"
                android:focusable="true"
                android:scaleType="center"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

        </androidx.constraintlayout.widget.ConstraintLayout>
        <!-- endregion call controls -->

        <ImageButton
            android:id="@+id/button_call_toggle_mic"
            android:layout_width="@dimen/call_activity_small_button_size"
            android:layout_height="@dimen/call_activity_small_button_size"
            android:layout_marginRight="16dp"
            android:layout_marginBottom="16dp"
            android:background="@drawable/ic_circle_lockscreen_semi_medium"
            android:contentDescription="@string/voip_toggle_mic"
            android:focusable="true"
            android:foreground="@drawable/selector_avatar"
            android:scaleType="center"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:srcCompat="@drawable/ic_keyboard_voice_outline"
            app:tint="@android:color/white" />

    </androidx.constraintlayout.widget.ConstraintLayout>

</androidx.constraintlayout.widget.ConstraintLayout>