Player interface abstracts MediaPlayer and ExoPlayer.

1 IPlayer.kt

import android.content.Context
import android.graphics.SurfaceTexture
import android.net.Uri
import android.view.Surface

interface IPlayer {

    /**
     * コンテンツの全体時間を取得する。単位はミリ秒。
     */
    val duration: Long

    /**
     * 現在の再生時間を取得する。単位はミリ秒。
     */
    var currentPosition: Long

    /**
     * 現在再生中かどうかを取得する。
     */
    val isPlaying: Boolean

    /**
     * 音量
     */
    var volume: Float

    /**
     * 再生完了時のコールバック
     */
    var onCompletion: (() -> Unit)?

    /**
     * 一時停止する。
     */
    fun pause()

    /**
     * 再生を開始する。
     */
    fun start()

    /**
     * 停止する。
     */
    fun stop()

    /**
     * 読み込む。
     */
    fun load(uri: Uri)

    /**
     * リソースを解放する。
     */
    fun release()

    /**
     * 出力先を指定する。
     */
    fun setOutput(surfaceTexture: SurfaceTexture)

    /**
     * 出力先を指定する。
     */
    fun setOutput(surface: Surface)
}

2 MediaPlayerImpl.kt

class MediaPlayerImpl(
        private val context: Context,
        private val mp: MediaPlayer) : IPlayer {

    private var surface: Surface? = null

    override val duration: Long
        get() = mp.duration.toLong()

    override var currentPosition: Long
        set(value) = mp.seekTo(value.toInt())
        get() = mp.currentPosition.toLong()

    override val isPlaying: Boolean
        get() = mp.isPlaying

    override var volume: Float = 1.0f
        set(value) {
            field = value
            mp.setVolume(value, value)
        }

    override var onCompletion: (() -> Unit)? = null
        set(value) {
            field = value
            if (value != null) {
                mp.setOnCompletionListener { value() }
            } else {
                mp.setOnCompletionListener(null)
            }
        }

    override fun pause() = mp.pause()

    override fun start() = mp.start()

    override fun stop() = mp.stop()

    override fun load(uri: Uri) {
        mp.reset()
        mp.setDataSource(context, uri)
        mp.prepare()
    }

    override fun release() {
        surface?.release()
        mp.release()
    }

    override fun setOutput(surfaceTexture: SurfaceTexture) {
        surface?.release()
        surface = Surface(surfaceTexture)
        mp.setSurface(surface)
    }

    override fun setOutput(surface: Surface) {
        this.surface?.release()
        this.surface = surface
        mp.setSurface(surface)
    }
}

3 ExoPlayerImpl.kt

class ExoPlayerImpl(
        private val context: Context,
        private val exoPlayer: SimpleExoPlayer) : IPlayer, Player.EventListener {

    private val userAgent = Util.getUserAgent(context, context.applicationInfo.name)
    private var surface: Surface? = null

    override val duration: Long
        get() = exoPlayer.duration

    override var currentPosition: Long
        set(value) = exoPlayer.seekTo(value)
        get() = exoPlayer.currentPosition

    override val isPlaying: Boolean
        get() = exoPlayer.playWhenReady

    override var volume: Float
        get() = exoPlayer.volume
        set(value) {
            exoPlayer.volume = value
        }

    override var onCompletion: (() -> Unit)? = null
        set(value) {
            field = value
            if (value != null) {
                exoPlayer.addListener(this)
            } else {
                exoPlayer.removeListener(this)
            }
        }

    override fun pause() {
        exoPlayer.playWhenReady = false
    }

    override fun start() {
        exoPlayer.playWhenReady = true
    }

    override fun stop() = exoPlayer.stop()

    override fun load(uri: Uri) {
        val dataSourceFactory = DefaultDataSourceFactory(context, userAgent)
        val extractorsFactory = DefaultExtractorsFactory()
        val mediaSource = ExtractorMediaSource(uri, dataSourceFactory, extractorsFactory, null, null)
        exoPlayer.prepare(mediaSource)
    }

    override fun release() {
        surface?.release()
        exoPlayer.release()
    }

    override fun setOutput(surfaceTexture: SurfaceTexture) {
        surface?.release()
        surface = Surface(surfaceTexture)
        exoPlayer.setVideoSurface(surface)
    }

    override fun setOutput(surface: Surface) {
        this.surface?.release()
        this.surface = surface
        exoPlayer.setVideoSurface(surface)
    }

    override fun onPlayerStateChanged(playWhenReady: Boolean, playbackState: Int) {
        when (playbackState) {
            Player.STATE_ENDED -> onCompletion?.invoke()
        }
    }

    override fun onPlaybackParametersChanged(playbackParameters: PlaybackParameters?) {}
    override fun onTracksChanged(trackGroups: TrackGroupArray?, trackSelections: TrackSelectionArray?) {}
    override fun onPlayerError(error: ExoPlaybackException?) {}
    override fun onLoadingChanged(isLoading: Boolean) {}
    override fun onPositionDiscontinuity() {}
    override fun onRepeatModeChanged(repeatMode: Int) {}
    override fun onTimelineChanged(timeline: Timeline?, manifest: Any?) {}
}