player = ExoPlayerFactory.newSimpleInstance(context, DefaultTrackSelector())
    .apply {
       ...
    }

fun buildMediaSource(): MediaSource {
    val uriList = mutableListOf<MediaSource>()
    MediaCatalog.list.forEach {
        uriList.add(createExtractorMediaSource(it.mediaUri!!))
    }
    return ConcatenatingMediaSource(*uriList.toTypedArray())
}

private fun createExtractorMediaSource(uri: Uri): MediaSource {
    return ExtractorMediaSource.Factory(
            DefaultDataSourceFactory(context, "videoapp")).createMediaSource(uri)
}