ByteArraySampleSource used in ExoPlayer TextRenderer for renderering local subtitle (TTML) files.

ByteArraySampleSource

import android.annotation.TargetApi;
import android.content.Context;
import android.os.AsyncTask;

import com.google.android.exoplayer.FormatHolder;
import com.google.android.exoplayer.SampleHolder;
import com.google.android.exoplayer.SampleSource;
import com.google.android.exoplayer.TrackInfo;
import com.google.android.exoplayer.TrackRenderer;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Map;
import java.util.UUID;

/**
 * Simple ByteArray SampleSource implementation that loads entire TTML file into ByteArray.
 */
public class ByteArraySampleSource extends AsyncTask<Void, Void, Void> implements SampleSource {

    private static final int TRACK_STATE_DISABLED = 0;
    private static final int TRACK_STATE_ENABLED = 1;
    private static final int TRACK_STATE_FORMAT_SENT = 2;

    private long seekTimeUs;
    private final byte[] bytes;

    public ByteArraySampleSource(byte[] bytes) {
        this.bytes = bytes;
    }

    @Override
    public boolean prepare() throws IOException {
        return true;
    }

    @Override
    public int getTrackCount() {
        return 1;
    }

    @Override
    public TrackInfo getTrackInfo(int track) {
        return null;
    }

    @Override
    public void enable(int track, long timeUs) {
        seekToUs(timeUs);
    }

    @Override
    public boolean continueBuffering(long playbackPositionUs) {
        return true;
    }

    @Override
    public int readData(int track, long playbackPositionUs, FormatHolder formatHolder,
                        SampleHolder sampleHolder, boolean onlyReadDiscontinuity) {
        if (sampleHolder.data != null) {
            sampleHolder.size = bytes.length;
            sampleHolder.data = ByteBuffer.wrap(new byte[bytes.length]);
        }
        seekTimeUs = -1;
        return SAMPLE_READ;
    }

    @TargetApi(18)
    private Map<UUID, byte[]> getPsshInfoV18() {
        return null;
    }

    @Override
    public void disable(int track) {
        //Not implemented
    }

    @Override
    public void seekToUs(long timeUs) {
        if (seekTimeUs != timeUs) {
            seekTimeUs = timeUs;
        }
    }

    @Override
    public long getBufferedPositionUs() {
        return TrackRenderer.UNKNOWN_TIME_US;
    }

    @Override
    public void release() {

    }

    @Override
    protected Void doInBackground(Void... params) {
        return null;
    }
}

@anotherhale thanks for this code. It's the only thing I could find to point me on the right track. I did need to do some modifications to it though to get it work. I mentioned it here: google/ExoPlayer#39
posting it here as well:

Thought I would post this here since trying to find documentation on adding an external caption file is very hard:
https://gist.github.com/triwav/ba72e99e5181427f4645

And to use it I'm doing:
try
{
URL url = new URL(video.getClosedCaptionUrl());
HttpSampleSource subtitleSource = new HttpSampleSource(url, "text/vtt");
textRenderer = new TextTrackRenderer(subtitleSource, new WebvttParser(), this, getContext().getApplicationContext().getMainLooper());
player.prepare(videoRenderer, audioRenderer, textRenderer);
} catch (MalformedURLException e)
{
player.prepare(videoRenderer, audioRenderer);
}

Note that I am having to pass in the mime type which is less than ideal but getTrackInfo could get called before the load has completed resulting in my case the webvtt file getting ignored by the subtitle parser. One bug is that when it gets to the end of the video it will just hang there. I'm currently dealing with this with this code in my onText method:
// Bug manually dealing with for now
int playerPosition = player.getCurrentPosition();
if (previousOnTextTime == playerPosition)
{
player.setRendererEnabled(TYPE_TEXT, false);
}