Customization

To control Transformer's behavior, you can configure options in the API surface or replace pieces of functionality completely by writing custom implementations of interfaces and passing those in. This page describes some examples.

Control codec configuration

By default, Transformer will fall back to a supported resolution if the device's hardware encoder doesn't accept the requested output resolution. For example, Transformer can align the output width and height to be a multiple of 2 or 16 as is often required by hardware encoders. You can turn off this behavior so that Transformer instead throws an error if it can't produce the required output resolution:

transformerBuilder.setEncoderFactory(
  DefaultEncoderFactory.Builder(context).setEnableFallback(false).build()
)
Customization.kt

transformerBuilder.setEncoderFactory(
    new DefaultEncoderFactory.Builder(context).setEnableFallback(false).build());
Customization.java

Similarly, the DefaultEncoderFactory also supports using custom encoding settings with the setRequestedVideoEncoderSettings option.

You can also completely replace the factories for encoders and decoders to get full control over how the codecs are set up.

Custom muxers

You can set a custom muxer for writing media containers by calling Transformer.setMuxerFactory. For example, if you implement your own muxer at the application level, you can write a wrapper that implements the Muxer interface and then use setMuxerFactory to inject it into Transformer.

If your custom muxer supports writing negative timestamps in MP4 edit lists, you should ensure that Muxer.Factory#supportsWritingNegativeTimestampsInEditList returns true. This enables Transformer to perform optimizations, such as trim-only edits using MP4 edit lists, without needing to re-encode the video. For the default InAppMp4Muxer, this is already supported.