Simplify subtitle loading with a SingleSampleSource.

Issue: #587

library/src/main/java/com/google/android/exoplayer/SingleSampleSource.java

+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer;
+
+import com.google.android.exoplayer.SampleSource.SampleSourceReader;
+import com.google.android.exoplayer.upstream.DataSource;
+import com.google.android.exoplayer.upstream.DataSpec;
+import com.google.android.exoplayer.upstream.Loader;
+import com.google.android.exoplayer.upstream.Loader.Loadable;
+
+import android.net.Uri;
+import android.os.SystemClock;
+
+import java.io.IOException;
+import java.util.Arrays;
+
+/**
+ * A {@link SampleSource} that loads the data at a given {@link Uri} as a single sample.
+ */
+public final class SingleSampleSource implements SampleSource, SampleSourceReader, Loader.Callback,
+    Loadable {
+
+  /**
+   * The default minimum number of times to retry loading data prior to failing.
+   */
+  public static final int DEFAULT_MIN_LOADABLE_RETRY_COUNT = 3;
+
+  /**
+   * The initial size of the allocation used to hold the sample data.
+   */
+  private static final int INITIAL_SAMPLE_SIZE = 1;
+
+  private final Uri uri;
+  private final DataSource dataSource;
+  private final MediaFormat format;
+  private final TrackInfo trackInfo;
+  private final int minLoadableRetryCount;
+
+  private byte[] sampleData;
+  private int sampleSize;
+  private boolean pendingSample;
+
+  private boolean loadingFinished;
+  private Loader loader;
+  private IOException currentLoadableException;
+  private int currentLoadableExceptionCount;
+  private long currentLoadableExceptionTimestamp;
+
+  public SingleSampleSource(Uri uri, DataSource dataSource, MediaFormat format) {
+    this(uri, dataSource, format, DEFAULT_MIN_LOADABLE_RETRY_COUNT);
+  }
+
+  public SingleSampleSource(Uri uri, DataSource dataSource, MediaFormat format,
+      int minLoadableRetryCount) {
+    this.uri = uri;
+    this.dataSource = dataSource;
+    this.format = format;
+    this.minLoadableRetryCount = minLoadableRetryCount;
+    trackInfo = new TrackInfo(format.mimeType, format.durationUs);
+    sampleData = new byte[INITIAL_SAMPLE_SIZE];
+  }
+
+  @Override
+  public SampleSourceReader register() {
+    return this;
+  }
+
+  @Override
+  public boolean prepare(long positionUs) {
+    if (loader == null) {
+      loader = new Loader("Loader:" + format.mimeType);
+    }
+    return true;
+  }
+
+  @Override
+  public int getTrackCount() {
+    return 1;
+  }
+
+  @Override
+  public TrackInfo getTrackInfo(int track) {
+    return trackInfo;
+  }
+
+  @Override
+  public void enable(int track, long positionUs) {
+    pendingSample = true;
+    clearCurrentLoadableException();
+    maybeStartLoading();
+  }
+
+  @Override
+  public boolean continueBuffering(int track, long positionUs) {
+    maybeStartLoading();
+    return loadingFinished;
+  }
+
+  @Override
+  public void maybeThrowError() throws IOException {
+    if (currentLoadableException != null && currentLoadableExceptionCount > minLoadableRetryCount) {
+      throw currentLoadableException;
+    }
+  }
+
+  @Override
+  public int readData(int track, long positionUs, MediaFormatHolder formatHolder,
+      SampleHolder sampleHolder, boolean onlyReadDiscontinuity) {
+    if (onlyReadDiscontinuity) {
+      return NOTHING_READ;
+    } else if (!pendingSample) {
+      return END_OF_STREAM;
+    } else if (!loadingFinished) {
+      return NOTHING_READ;
+    } else {
+      sampleHolder.timeUs = 0;
+      sampleHolder.size = sampleSize;
+      sampleHolder.flags = C.SAMPLE_FLAG_SYNC;
+      if (sampleHolder.data == null || sampleHolder.data.capacity() < sampleSize) {
+        sampleHolder.replaceBuffer(sampleHolder.size);
+      }
+      sampleHolder.data.put(sampleData, 0, sampleSize);
+      return SAMPLE_READ;
+    }
+  }
+
+  @Override
+  public void seekToUs(long positionUs) {
+    pendingSample = true;
+  }
+
+  @Override
+  public long getBufferedPositionUs() {
+    return loadingFinished ? TrackRenderer.END_OF_TRACK_US : 0;
+  }
+
+  @Override
+  public void disable(int track) {
+    pendingSample = false;
+  }
+
+  @Override
+  public void release() {
+    if (loader != null) {
+      loader.release();
+      loader = null;
+    }
+  }
+
+  // Private methods.
+
+  private void maybeStartLoading() {
+    if (loadingFinished || !pendingSample || loader.isLoading()) {
+      return;
+    }
+    if (currentLoadableException != null) {
+      long elapsedMillis = SystemClock.elapsedRealtime() - currentLoadableExceptionTimestamp;
+      if (elapsedMillis < getRetryDelayMillis(currentLoadableExceptionCount)) {
+        return;
+      }
+      clearCurrentLoadableException();
+    }
+    loader.startLoading(this, this);
+  }
+
+  private void clearCurrentLoadableException() {
+    currentLoadableException = null;
+    currentLoadableExceptionCount = 0;
+  }
+
+  private long getRetryDelayMillis(long errorCount) {
+    return Math.min((errorCount - 1) * 1000, 5000);
+  }
+
+  // Loader.Callback implementation.
+
+  @Override
+  public void onLoadCompleted(Loadable loadable) {
+    loadingFinished = true;
+    clearCurrentLoadableException();
+  }
+
+  @Override
+  public void onLoadCanceled(Loadable loadable) {
+    // Never happens.
+  }
+
+  @Override
+  public void onLoadError(Loadable loadable, IOException e) {
+    currentLoadableException = e;
+    currentLoadableExceptionCount++;
+    currentLoadableExceptionTimestamp = SystemClock.elapsedRealtime();
+    maybeStartLoading();
+  }
+
+  // Loadable implementation.
+
+  @Override
+  public void cancelLoad() {
+    // Never happens.
+  }
+
+  @Override
+  public boolean isLoadCanceled() {
+    return false;
+  }
+
+  @Override
+  public void load() throws IOException, InterruptedException {
+    // We always load from the beginning, so reset the sampleSize to 0.
+    sampleSize = 0;
+    try {
+      // Create and open the input.
+      dataSource.open(new DataSpec(uri));
+      // Load the sample data.
+      int result = 0;
+      while (result != C.RESULT_END_OF_INPUT) {
+        sampleSize += result;
+        if (sampleSize == sampleData.length) {
+          sampleData = Arrays.copyOf(sampleData, sampleData.length * 2);
+        }
+        result = dataSource.read(sampleData, sampleSize, sampleData.length - sampleSize);
+      }
+    } finally {
+      dataSource.close();
+    }
+  }
+
+}