Extract encoded samples

The MediaExtractorCompat class is a drop-in replacement for the platform's MediaExtractor class and provides identical APIs and functionality. It facilitates extraction of demuxed, typically encoded, media data from a data source.

It separates a container file (like an MP4 or MKV) into its individual tracks, such as video, audio, and subtitles. The extractor then reads the raw, encoded data from these tracks as a sequence of samples (for example, a single compressed video frame or block of audio) before they are sent to a decoder.

Common use cases include:

  • Transcoding or Remuxing: Reading encoded samples from a track to either change the codec (transcoding) or repackage the streams into a new container (remuxing), such as converting an MP4 file to MKV.
  • Selective content extraction: Isolating and saving a single track, such as extracting an audio stream from a video file.
  • Low-level debugging: Inspecting individual samples to debug file corruption, timestamp issues, or other problems.
  • Building custom players: For niche use cases, building a custom player with full control over the media pipeline.

Overview

The following code sample shows how to use MediaExtractorCompat:

Kotlin

fun extractSamples(context: Context, mediaPath: String) {
    val extractor = MediaExtractorCompat(context)
    try {
        // 1. Setup the extractor
        extractor.setDataSource(mediaPath)

        // Find and select available tracks
        for (i in 0 until extractor.trackCount) {
            val format = extractor.getTrackFormat(i)
            extractor.selectTrack(i)
        }

        // 2. Process samples
        val buffer = ByteBuffer.allocate(10 * 1024 * 1024)
        while (true) {
            // Read an encoded sample into the buffer.
            val bytesRead = extractor.readSampleData(buffer, 0)
            if (bytesRead < 0) break

            // Access sample metadata
            val trackIndex = extractor.sampleTrackIndex
            val presentationTimeUs = extractor.sampleTime
            val sampleSize = extractor.sampleSize

            extractor.advance()
        }
    } catch (e: IOException) {
        throw RuntimeException(e)
    } finally {
        // 3. Release the extractor
        extractor.release()
    }
}

Java

public void extractSamples(Context context, String mediaPath) {
    MediaExtractorCompat extractor = new MediaExtractorCompat(context);
    try {
        // 1. Setup the extractor
        extractor.setDataSource(mediaPath);

        // Find and select available tracks
        for (int i = 0; i < extractor.getTrackCount(); i++) {
            MediaFormat format = extractor.getTrackFormat(i);
            extractor.selectTrack(i);
        }

        // 2. Process samples
        ByteBuffer buffer = ByteBuffer.allocate(10 * 1024 * 1024);
        while (true) {
            // Read an encoded sample into the buffer.
            int bytesRead = extractor.readSampleData(buffer, 0);
            if (bytesRead < 0) break;

            // Access sample metadata
            int trackIndex = extractor.getSampleTrackIndex();
            long presentationTimeUs = extractor.getSampleTime();
            long sampleSize = extractor.getSampleSize();

            extractor.advance();
        }
    } catch (IOException e) {
        throw new RuntimeException(e);
    } finally {
        // 3. Release the extractor
        extractor.release();
    }
}