Network stacks

ExoPlayer is commonly used for streaming media over the internet. It supports multiple network stacks for making its underlying network requests. Your choice of network stack can have a significant impact on streaming performance.

This page outlines how to configure ExoPlayer to use your network stack of choice, lists the available options, provides some guidance on how to choose a network stack for your app, and explains how to enable caching for streamed media.

Configuring ExoPlayer to use a specific network stack

ExoPlayer loads data through DataSource components, which it obtains from DataSource.Factory instances that are injected from app code.

If your app only needs to play http(s) content, selecting a network stack is as simple as updating any DataSource.Factory instances that your app injects to be instances of the HttpDataSource.Factory that corresponds to the network stack you wish to use. If your app also needs to play non-http(s) content, such as local files, use DefaultDataSource.Factory:

DefaultDataSource.Factory(
  ...
  /* baseDataSourceFactory= */ PreferredHttpDataSource.Factory(...))

new DefaultDataSource.Factory(
    ...
    /* baseDataSourceFactory= */ new PreferredHttpDataSource.Factory(...));

In this example, PreferredHttpDataSource.Factory is the factory corresponding to your preferred network stack. The DefaultDataSource.Factory layer adds in support for non-http(s) sources such as local files.

The following example shows how to build an ExoPlayer that will use the Cronet network stack and also support playback of non-http(s) content.

// Given a CronetEngine and Executor, build a CronetDataSource.Factory.
val cronetDataSourceFactory = CronetDataSource.Factory(cronetEngine, executor)

// Wrap the CronetDataSource.Factory in a DefaultDataSource.Factory, which adds
// in support for requesting data from other sources (such as files, resources,
// etc).
val dataSourceFactory =
  DefaultDataSource.Factory(context, /* baseDataSourceFactory= */ cronetDataSourceFactory)

// Inject the DefaultDataSource.Factory when creating the player.
val player =
  ExoPlayer.Builder(context)
    .setMediaSourceFactory(
      DefaultMediaSourceFactory(context).setDataSourceFactory(dataSourceFactory)
    )
    .build()

// Given a CronetEngine and Executor, build a CronetDataSource.Factory.
CronetDataSource.Factory cronetDataSourceFactory =
    new CronetDataSource.Factory(cronetEngine, executor);

// Wrap the CronetDataSource.Factory in a DefaultDataSource.Factory, which adds
// in support for requesting data from other sources (such as files, resources,
// etc).
DefaultDataSource.Factory dataSourceFactory =
    new DefaultDataSource.Factory(
        context, /* baseDataSourceFactory= */ cronetDataSourceFactory);

// Inject the DefaultDataSource.Factory when creating the player.
ExoPlayer player =
    new ExoPlayer.Builder(context)
        .setMediaSourceFactory(
            new DefaultMediaSourceFactory(context).setDataSourceFactory(dataSourceFactory))
        .build();

Supported network stacks

ExoPlayer provides direct support for HttpEngine, Cronet, OkHttp, and Android's built-in default network stack. ExoPlayer can also be extended to support any other network stack that works on Android.

HttpEngine

HttpEngine is the recommended default network stack on Android from API 34 (or S extensions 7). In most cases, it is using the Cronet network stack internally, supporting HTTP, HTTP/2, and HTTP/3 over QUIC protocols.

ExoPlayer supports HttpEngine with its HttpEngineDataSource.Factory. You can inject this data source factory as described in Configuring ExoPlayer to use a specific network stack.

Cronet

Cronet is the Chromium network stack made available to Android apps as a library. Cronet takes advantage of multiple technologies that reduce the latency and increase the throughput of the network requests that your app needs to work, including those made by ExoPlayer. It natively supports the HTTP, HTTP/2, and HTTP/3 over QUIC protocols. Cronet is used by some of the world's biggest streaming apps, including YouTube.

ExoPlayer supports Cronet via its Cronet library. See the library's README.md for detailed instructions on how to use it. Note that the Cronet library is able to use three underlying Cronet implementations:

1. Google Play Services: We recommend using this implementation in most cases, and falling back to Android's built-in network stack (DefaultHttpDataSource) if Google Play Services is not available.
2. Cronet Embedded: May be a good choice if a large percentage of your users are in markets where Google Play Services is not widely available, or if you want to control the exact version of the Cronet implementation being used. The major disadvantage of Cronet Embedded is that it adds approximately 8MB to your app.
3. Cronet Fallback: The fallback implementation of Cronet implements Cronet's API as a wrapper around Android's built-in network stack. It should not be used with ExoPlayer, since using Android's built-in network stack directly (by using DefaultHttpDataSource) is more efficient.

OkHttp

OkHttp is another modern network stack that is widely used by many popular Android apps. It supports HTTP and HTTP/2, but does not yet support HTTP/3 over QUIC.

ExoPlayer supports OkHttp through its OkHttp library. See the library's README.md for detailed instructions on how to use it. When using the OkHttp library, the network stack is embedded within the app. This is similar to Cronet Embedded, however OkHttp is significantly smaller, adding under 1MB to your app.

Android's built-in network stack

ExoPlayer supports use of Android's built-in network stack with DefaultHttpDataSource and DefaultHttpDataSource.Factory, which are part of the core ExoPlayer library.

The exact network stack implementation depends on the software running on the underlying device. On most devices only HTTP is supported (that is, HTTP/2 and HTTP/3 over QUIC are not supported).

Other network stacks

Apps can also integrate other network stacks with ExoPlayer. To do this, implement an HttpDataSource that wraps the network stack, together with a corresponding HttpDataSource.Factory. ExoPlayer's Cronet and OkHttp libraries are good examples of how to do this.

When integrating with a pure Java network stack, it's a good idea to implement a DataSourceContractTest to check that your HttpDataSource implementation behaves correctly. OkHttpDataSourceContractTest in the OkHttp library is a good example of how to do this.

Choosing a network stack

The following table outlines the pros and cons of the network stacks supported by ExoPlayer.

The HTTP/2 and HTTP/3 over QUIC protocols can significantly improve media streaming performance. In particular, when streaming adaptive media that is distributed using a content distribution network (CDN), there are cases for which use of these protocols can allow CDNs to operate much more efficiently. For this reason, HttpEngine's and Cronet's support for both HTTP/2 and HTTP/3 over QUIC (and OkHttp's support for HTTP/2), is a major benefit compared to using Android's built-in network stack, provided the servers on which the content is hosted also support these protocols.

When considering media streaming in isolation, we recommend use of HttpEngine or Cronet provided by Google Play Services falling back to DefaultHttpDataSource if Google Play Services is unavailable. This recommendation strikes a good balance between enabling use of HTTP/2 and HTTP/3 over QUIC on most devices, and avoiding a significant increase in APK size. There are exceptions to this recommendation. For cases where Google Play Services is likely to be unavailable on a significant fraction of devices that will be running your app, using Cronet Embedded or OkHttp may be more appropriate. Use of the built-in network stack may be acceptable if APK size is a critical concern, or if media streaming is only a minor part of your app's functionality.

Beyond just media, it's normally a good idea to choose a single network stack for all of the networking performed by your app. This allows resources (such as sockets) to be efficiently pooled and shared between ExoPlayer and other app components.

Because your app will most likely need to perform networking not related to media playback, your choice of network stack should ultimately factor in our recommendations above for media streaming in isolation, the requirements of any other components that perform networking, and their relative importance to your app.

Caching media

ExoPlayer supports caching loaded bytes to disk to prevent repeatedly loading the same bytes from network. This is useful when seeking back in the current media or repeating the same item.

Caching requires a SimpleCache instance pointing to a dedicated cache directory and a CacheDataSource.Factory:

// Note: This should be a singleton in your app.
val databaseProvider = StandaloneDatabaseProvider(context)

// An on-the-fly cache should evict media when reaching a maximum disk space limit.
val cache =
    SimpleCache(
        downloadDirectory, LeastRecentlyUsedCacheEvictor(maxBytes), databaseProvider)

// Configure the DataSource.Factory with the cache and factory for the desired HTTP stack.
val cacheDataSourceFactory =
    CacheDataSource.Factory()
        .setCache(cache)
        .setUpstreamDataSourceFactory(httpDataSourceFactory)

// Inject the DefaultDataSource.Factory when creating the player.
val player =
    ExoPlayer.Builder(context)
        .setMediaSourceFactory(
            DefaultMediaSourceFactory(context).setDataSourceFactory(cacheDataSourceFactory))
        .build()

// Note: This should be a singleton in your app.
DatabaseProvider databaseProvider = new StandaloneDatabaseProvider(context);

// An on-the-fly cache should evict media when reaching a maximum disk space limit.
Cache cache =
    new SimpleCache(
        downloadDirectory, new LeastRecentlyUsedCacheEvictor(maxBytes), databaseProvider);

// Configure the DataSource.Factory with the cache and factory for the desired HTTP stack.
DataSource.Factory cacheDataSourceFactory =
    new CacheDataSource.Factory()
        .setCache(cache)
        .setUpstreamDataSourceFactory(httpDataSourceFactory);

// Inject the DefaultDataSource.Factory when creating the player.
ExoPlayer player =
    new ExoPlayer.Builder(context)
        .setMediaSourceFactory(
            new DefaultMediaSourceFactory(context).setDataSourceFactory(cacheDataSourceFactory))
        .build();