How to precache a list of videos before playing them in a recyclerview of exoplayer?

I am using exoplayer in recyclerview to render a list of videos. This recyclerview is rendered in an activity and I know the list of video urls before opening the activity.

I want to be able to preload or cache the videos before going to that activity. The videos are usually less than 1 minute. So I am not looking for a solution to smooth stream videos. I just want the videos to be in the cache before opening the activity so that once the recyclerview opens the videos start playing without any buffering just like in tiktok.

I found a way to cache already played videos using LocalCacheDataSourceFactory in

MediaSource videoSource =
 new ExtractorMediaSource(Uri.parse(mediaUrl),
                            new LocalCacheDataSourceFactory(context, 100 * 1024 * 1024, 5 * 1024 * 1024), new DefaultExtractorsFactory(), null, null);

This only allows me to cache the videos that are already played but not preloading or precaching them.

Found this medium article from exoplayer team but no other example integration for my specific requirement. article

Checkout this article. I have written a step by step guide to preload/precache videos using Exoplayer2.

In your case you must create a recursion or looping of caching method inside a background thread.

Video preloading/ precaching using Exoplayer 2 in Android

I have achieved this in my own app. Follow these steps:

1. add this video caching dependency:

     implementation 'com.danikula:videocache:2.7.1'
   

2. Setup dependency like this:
   It is advised that you do this in the application class:

    private HttpProxyCacheServer proxy;

    public static HttpProxyCacheServer getProxy(Context context) {
        AppController app = (AppController) context.getApplicationContext();
        return app.proxy == null ? (app.proxy = app.newProxy()) : app.proxy;
    }
    private HttpProxyCacheServer newProxy() {
        return new HttpProxyCacheServer(this);
    }

//Note that you need to have a single instance of HttpProxyCacheServer. 
//Note the library is tradinally meant to allow you to cache a video so exoplayer does not re-buffer it every single time you scroll to recycler item. 

3. Then setup your exoplayer like this:

   a.

   HttpProxyCacheServer proxyServer; // maintain a single instance of this. you can init this in oncreate method: 
   public ViewRecommendedShortVideosAdapter(Context context) {
   
       proxyServer = AppController.getProxy(context);
      }
   

   b. In your method to play exoplayer file:

   String streamingURL = shortVideo.getStreamingURL();
       String proxyURL = proxyServer.getProxyUrl(streamingURL); 
   
       MediaItem mediaItem = MediaItem.fromUri(proxyURL); // you are now crating the media item from the proxy url you get by calling getProxyUrl on your proxyServer instance. 
       exoPlayer.setMediaItem(mediaItem);
       exoPlayer.prepare();
       exoPlayer.setPlayWhenReady(true);
   

Note: the above still only gives you caching of the video once it has been played, and not caching of yet to play videos.

4. To cache yet to play videos, do this:

   a. you can cache only the next video in the recycler data arraylist (this helps save user internet costs) or you can cache the whole (I don't recommend, cos of data costs on users).

   b. To cache the next video, create a method such as prepareNextVideo(), this will contain the logic to cache the next video. you will call this method in the original method to play an exoplayer media item. (maybe after setting up the first media item and set exoplayer.play()).

   c. the code in the prepareNextVideo():

    private void prepareNextVideo(int currentPosition){
       URL url = null;
       try {
           ShortVideo shortVideo = videosArrayList.get(currentPosition+1); //you can put some if conditions here to check if the element exists. but a try cache should handle it to. 
   
           url = new URL(proxyServer.getProxyUrl(shortVideo.getStreamingURL())); // we are using our proxy url again. 
   
           InputStream inputStream = url.openStream();
           int bufferSize = 1024; 
           byte[] buffer = new byte[bufferSize];
           int length = 0;
           while ((length = inputStream.read(buffer)) != -1) {
               //nothing to do here. you are just reading the stream. 
           }
   
   
       } catch (Exception e) {
           e.printStackTrace();
   
           //can fetch
       }
   }
   

Finally, simply call this method to buffer the next video. you can also put it in a loop, run asynchronously if you want to buffer all the videos.