Android convert exo to mp4 after download dash

I have downloaded a Dynamic Adaptive Streaming over HTTP (DASH) via android DashDownloader class that is provided by exo player.

SimpleCache cache = new SimpleCache(file.getAbsoluteFile(), new NoOpCacheEvictor());
DefaultHttpDataSourceFactory factory = new DefaultHttpDataSourceFactory("ExoPlayer", null);
DownloaderConstructorHelper constructorHelper = new DownloaderConstructorHelper(cache, factory); // Create a downloader for the first representation of the first adaptation set of the first
// period.
DashDownloader dashDownloader = new DashDownloader(Uri.parse(url), Collections.singletonList(new RepresentationKey(0, 0, 0)), constructorHelper);
dashDownloader.download();

Above code save many chunk .exo files into provided directory, How can i convert this files to single mp4 file?