Getting started

Getting started with Transformer consists of the following steps:

1. Add Media3 Transformer as a dependency in your project.
2. Build an EditedMediaItem representing the media to process and edits to apply to it.
3. Build a Transformer, describing the required output and a listener for completion and error events.
4. Start the export operation, passing in the EditedMediaItem to edit and an output path. During export, you can query the current progress or cancel the operation.
5. When exporting finishes, handle the output as needed. For example, you can share the output to another app or upload it to a server.

Read on for more detail about these steps, and see TransformerActivity in the transformer demo app for a complete example.

Add Media3 Transformer as a dependency

The easiest way to get started using Transformer is to add gradle dependencies on the library in the build.gradle file of your app module:

implementation "androidx.media3:media3-transformer:1.2.0"
implementation "androidx.media3:media3-effect:1.2.0"
implementation "androidx.media3:media3-common:1.2.0"

where 1.2.0 is your preferred version. The latest version can be found by consulting the release notes.

More information on the library modules that are available can be found on the Google Maven AndroidX Media3 page.

Turn on Java 8 support

If not enabled already, you need to turn on Java 8 support in all build.gradle files that depend on Transformer by adding the following to the android section:

compileOptions {
  targetCompatibility JavaVersion.VERSION_1_8
}

Start a transformation

Here's an example of creating an EditedMediaItem to remove audio for an input file, then creating and configuring a Transformer instance to export H.265/HEVC video, outputting the result to outputPath.

val inputMediaItem = MediaItem.fromUri("path_to_input_file")
val editedMediaItem =
    EditedMediaItem.Builder(inputMediaItem).setRemoveAudio(true).build()
val transformer = Transformer.Builder(context)
    .setVideoMimeType(MimeTypes.VIDEO_H265)
    .addListener(transformerListener)
    .build()
transformer.start(editedMediaItem, outputPath)

MediaItem inputMediaItem = MediaItem.fromUri("path_to_input_file");
EditedMediaItem editedMediaItem =
    new EditedMediaItem.Builder(inputMediaItem).setRemoveAudio(true).build();
Transformer transformer =
    new Transformer.Builder(context)
        .setVideoMimeType(MimeTypes.VIDEO_H265)
        .addListener(transformerListener)
        .build();
transformer.start(editedMediaItem, outputPath);

For more information about media items, see the ExoPlayer media items page. The input can be a progressive or an adaptive stream, but the output is always a progressive stream. For adaptive inputs, the highest-resolution tracks are always selected for the transformation. The input can be of any container format supported by ExoPlayer, but the output is always an MP4 file.

You can execute multiple export operations sequentially on the same Transformer instance, but concurrent exports with the same instance are not supported.

A note on threading

Transformer instances must be accessed from a single application thread, and the listener methods are called on the same thread. For the majority of cases, the application thread can just be the main thread of the application. Internally, Transformer does its work in the background and posts its calls to listener methods on the application thread.

Listen to events

The start method is asynchronous. It returns immediately and the app is notified of events through the listener passed to the Transformer builder.

val transformerListener: Transformer.Listener =
    object : Transformer.Listener {
  override fun onCompleted(composition: Composition, result: ExportResult) {
    playOutput()
  }

  override fun onError(composition: Composition, result: ExportResult,
                       exception: ExportException) {
    displayError(exception)
  }
}

Transformer.Listener transformerListener =
    new Transformer.Listener() {
      @Override
      public void onCompleted(Composition composition, ExportResult result) {
        playOutput();
      }

      @Override
      public void onError(Composition composition, ExportResult result,
          ExportException exception) {
        displayError(exception);
      }
    };

ExportResult includes information about the output file, including the file size and average bitrates for audio and video, as applicable.

Get progress updates

Call Transformer.getProgress to query the current progress of a transformation. The returned value indicates the progress state. If the progress state is PROGRESS_STATE_AVAILABLE, then the provided ProgressHolder is updated with the current progress percentage. The following example shows how to periodically query the progress of a transformation, where the updateProgressInUi method can be implemented to update a progress bar.

transformer.start(inputMediaItem, outputPath)
val progressHolder = ProgressHolder()
mainHandler.post(
    object : Runnable {
      override fun run() {
        val progressState: @ProgressState Int = transformer.getProgress(progressHolder)
        updateProgressInUi(progressState, progressHolder)
        if (progressState != Transformer.PROGRESS_STATE_NOT_STARTED) {
          mainHandler.postDelayed(/* r= */this,  /* delayMillis= */500)
        }
      }
    }
)

transformer.start(inputMediaItem, outputPath);
ProgressHolder progressHolder = new ProgressHolder();
mainHandler.post(
    new Runnable() {
      @Override
      public void run() {
        @Transformer.ProgressState int progressState = transformer.getProgress(progressHolder);
        updateProgressInUi(progressState, progressHolder);
        if (progressState != PROGRESS_STATE_NOT_STARTED) {
          mainHandler.postDelayed(/* r= */ this, /* delayMillis= */ 500);
        }
      }
    });

Cancel a transformation

If the user chooses to back out of an export flow, cancel the export operation with Transformer.cancel. Resources like hardware video codecs are limited, especially on lower-end devices, so it's important to do this to free up resources if the output isn't needed.