Implementations of SeekBarPreference features specific to media volume.

preference_seekbar.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="20dp">

    <TextView
        android:id="@+id/summary"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:maxLines="1"
        android:text="@string/setting_sound2"
        android:textAppearance="?android:attr/textAppearanceSmall"
        android:textColor="?android:attr/textColorSecondary" />

    <SeekBar
        android:id="@+id/seekbar"
        android:layout_marginTop="10dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

preferences.xml

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >
    <PreferenceCategory android:title="@string/setting_sound">
        <CheckBoxPreference
            android:defaultValue="true"
            android:key="@string/PREF_SOUND_ON"
            android:title="@string/setting_sound_on_title" />
        <com.sakurafish.parrot.callconfirm.Pref.SoundSeekBarPreference
            android:dependency="@string/PREF_SOUND_ON"
            android:key="@string/PREF_SOUND_VOLUME"
            android:title="@string/setting_sound_on_title" />
    </PreferenceCategory>
</PreferenceScreen>

SoundSeekBarPreference.java

/**
 * Copyright 2015-present Yukari Sakurai
 * <p/>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p/>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p/>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.sakurafish.parrot.callconfirm.Pref;

import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.Color;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffColorFilter;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.OvalShape;
import android.media.AudioManager;
import android.os.Build;
import android.preference.Preference;
import android.support.annotation.NonNull;
import android.util.AttributeSet;
import android.view.View;
import android.widget.SeekBar;

import com.sakurafish.common.lib.pref.Pref;
import com.sakurafish.parrot.callconfirm.R;
import com.sakurafish.parrot.callconfirm.utils.Utils;

import static android.os.Build.VERSION.SDK_INT;

/**
 * Save SeekBar's value to the preference. <br>
 * Thanks to MrBIMC's "MaterialSeekBarPreference" <br>
 * https://github.com/MrBIMC/MaterialSeekBarPreference
 */
public class SoundSeekBarPreference extends Preference implements SeekBar.OnSeekBarChangeListener {

    public interface OnVolumeChangedListerner {
        void onChanged();
    }

    private Context mContext;
    private OnVolumeChangedListerner mListerner;
    private int mMaxValue = 100;
    private int mMinValue = 0;
    private int mInterval = 1;
    private int mCurrentValue;
    private SeekBar mSeekBar;

    public SoundSeekBarPreference(Context context, AttributeSet attrs) {
        super(context, attrs);
        mContext = context;
        setLayoutResource(R.layout.preference_seekbar);
        setCurrentVolume();
    }

    public SoundSeekBarPreference(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mContext = context;
        setLayoutResource(R.layout.preference_seekbar);
        setCurrentVolume();
    }

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public SoundSeekBarPreference(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        mContext = context;
        setLayoutResource(R.layout.preference_seekbar);
        setCurrentVolume();
    }

    public void setOnVolumeChangedListerner(OnVolumeChangedListerner listerner) {
        mListerner = listerner;
    }

    public void removeOnVolumeChangedListerner() {
        mListerner = null;
    }

    private void setCurrentVolume() {
        AudioManager am = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);
        if (Pref.isExistKey(mContext, mContext.getString(R.string.PREF_SOUND_VOLUME))) {
            mCurrentValue = Pref.getPrefInt(mContext, mContext.getString(R.string.PREF_SOUND_VOLUME));
        } else {
            mCurrentValue = am.getStreamVolume(AudioManager.STREAM_MUSIC);
        }
        mMaxValue = am.getStreamMaxVolume(AudioManager.STREAM_MUSIC);
        Utils.logDebug("mCurrentValue:" + mCurrentValue + " mMaxValue:" + mMaxValue + " sysvol:" + am.getStreamVolume(AudioManager.STREAM_MUSIC));
    }

    @Override
    public void onBindView(@NonNull View view) {
        super.onBindView(view);

        mSeekBar = (SeekBar) view.findViewById(R.id.seekbar);
        mSeekBar.setMax(mMaxValue - mMinValue);
        mSeekBar.setOnSeekBarChangeListener(this);


        mSeekBar.setProgress(mCurrentValue - mMinValue);

        setSeekBarTintOnPreLollipop();

        if (!view.isEnabled()) {
            mSeekBar.setEnabled(false);
        }
    }

    public void setCurrentValue(int value) {
        mCurrentValue = value;
        super.persistInt(value);
        notifyChanged();
    }

    public int getCurrentValue() {
        return mCurrentValue;
    }

    static int pxFromDp(int dp, Context context) {
        return (int) (dp * context.getResources().getDisplayMetrics().density);
    }

    void setSeekBarTintOnPreLollipop() { //TMP: I hope google will introduce native seekbar tinting for appcompat users
        if (SDK_INT < 21) {
            Resources.Theme theme = getContext().getTheme();

            int attr = R.attr.colorAccent;
            int fallbackColor = Color.parseColor("#009688");
            int accent = theme.obtainStyledAttributes(new int[]{attr}).getColor(0, fallbackColor);

            ShapeDrawable thumb = new ShapeDrawable(new OvalShape());
            thumb.setIntrinsicHeight(pxFromDp(15, getContext()));
            thumb.setIntrinsicWidth(pxFromDp(15, getContext()));
            thumb.setColorFilter(new PorterDuffColorFilter(accent, PorterDuff.Mode.SRC_ATOP));
            mSeekBar.setThumb(thumb);

            Drawable progress = mSeekBar.getProgressDrawable();
            progress.setColorFilter(new PorterDuffColorFilter(accent, PorterDuff.Mode.MULTIPLY));
            mSeekBar.setProgressDrawable(progress);
        }
    }

    @Override
    public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {

        int newValue = progress + mMinValue;

        if (newValue > mMaxValue) newValue = mMaxValue;

        else if (newValue < mMinValue) newValue = mMinValue;

        else if (mInterval != 1 && newValue % mInterval != 0)
            newValue = Math.round(((float) newValue) / mInterval) * mInterval;

        // change rejected, revert to the previous value
        if (!callChangeListener(newValue)) {
            seekBar.setProgress(mCurrentValue - mMinValue);
            return;
        }

        // change accepted, store it
        mCurrentValue = newValue;
    }

    @Override
    public void onStartTrackingTouch(SeekBar seekBar) {

    }

    @Override
    public void onStopTrackingTouch(SeekBar seekBar) {
        notifyChanged();
        persistInt(mCurrentValue);
        if (mListerner != null) {
            mListerner.onChanged();
        }
    }
}

Usage.java

            final SoundSeekBarPreference volume = (SoundSeekBarPreference) findPreference(getString(R.string.PREF_SOUND_VOLUME));
            volume.setOnVolumeChangedListerner(new SoundSeekBarPreference.OnVolumeChangedListerner() {
                @Override
                public void onChanged() {
                    int index = Integer.parseInt(Pref.getPrefString(mContext, mContext.getString(R.string.PREF_SOUND)));
                    int voiceIdx = MyApplication.getSoundIds()[index];

                    MyApplication.getSoundManager().stop(voiceIdx);

                    AudioManager am = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);
                    int newVolume = Pref.getPrefInt(mContext, mContext.getString(R.string.PREF_SOUND_VOLUME));
                    am.setStreamVolume(AudioManager.STREAM_MUSIC, newVolume, 0);

                    MyApplication.getSoundManager().play(voiceIdx);
                }
            });