Supported formats

See the ExoPlayer supported formats page for an introduction to media formats in general. The same limitations on loading, extracting, and decoding streams apply with Transformer, though Transformer does not support ExoPlayer's bundled software decoder modules.

Transformer also relies on MediaCodec for encoding, and needs to multiplex, or mux, output media files, which limits the output formats supported. See MediaCodec video codecs for more information about encoding limitations and MediaMuxer for limitations that apply to the output media container. Transformer only outputs MP4 files.

By default, Transformer uses MediaMuxer, but a work-in-progress InAppMuxer is optionally available to avoid some of MediaMuxer's limitations around reference frame structures and supported sample formats. The default muxer will become the in-app muxer in a future release.

Special formats

Transformer supports handling input in newer media formats that provide special features compared to conventional formats.

Handling HDR videos

More and more devices now support HDR video capture, giving more vivid, accurate colors and a greater brightness range.

Transformer supports editing HDR videos from Android 13 (API level 33) onwards on devices with the required encoding support. When editing HDR videos, any GL video effects need to handle 16-bit floating point color components and BT.2020 color space. HDR_MODE_KEEP_HDR is the default mode when building the Composition. If HDR editing is not supported, the Transformer falls back to using HDR_MODE_TONE_MAP_HDR_TO_SDR_USING_OPEN_GL.

Converting HDR to SDR, also known as tone-mapping, is supported from Android 10 (API level 29) onwards on devices with the required decoding and OpenGL support. This is useful when sharing HDR media to other apps or services that don't support ingestion of HDR content. To enable tone-mapping using OpenGL call setHdrMode(HDR_MODE_TONE_MAP_HDR_TO_SDR_USING_OPEN_GL) when creating the Composition. From Android 12 (API level 31) onwards, MediaCodec also supports tone-mapping on some devices, including all devices running Android 13 or higher that can capture HDR video. To enable tone-mapping using MediaCodec call setHdrMode(HDR_MODE_TONE_MAP_HDR_TO_SDR_USING_MEDIACODEC).

Handling slow motion media

Slow-motion videos include metadata indicating the speed at which each section of the stream should be played. Flattening is the process of producing a new video stream based on the slow-motion video but where the sections are sped up or slowed down based on metadata, so that they play correctly even on players that don't apply slow motion metadata.

To flatten slow-motion streams, use the setFlattenForSlowMotion builder method on EditedMediaItem.

Kotlin

val editedMediaItem =
    EditedMediaItem.Builder(inputMediaItem).setFlattenForSlowMotion(true).build()
val transformer =
    Transformer.Builder(context).addListener(transformerListener).build()
transformer.start(editedMediaItem, outputPath)

Java

EditedMediaItem editedMediaItem =
    new EditedMediaItem.Builder(inputMediaItem).setFlattenForSlowMotion(true).build();
Transformer transformer =
    new Transformer.Builder(context).addListener(transformerListener).build();
transformer.start(editedMediaItem, outputPath);

This allows you to support slow-motion videos without having to worry about handling these special formats. All you need to do is to store and play the flattened version of the video instead of the original one.