1 files changed, 195 insertions, 0 deletions
diff --git a/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/source/hls/WebvttExtractor.java b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/source/hls/WebvttExtractor.java
new file mode 100644
index 0000000000..1d5e669a03
--- /dev/null
+++ b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/source/hls/WebvttExtractor.java
@@ -0,0 +1,195 @@
+/*
+ * Copyright (C) 2016 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 org.mozilla.thirdparty.com.google.android.exoplayer2.source.hls;
+
+import android.text.TextUtils;
+import androidx.annotation.Nullable;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.C;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.Format;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.ParserException;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.Extractor;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.ExtractorInput;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.ExtractorOutput;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.PositionHolder;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.SeekMap;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.TrackOutput;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.text.webvtt.WebvttParserUtil;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.util.Assertions;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.util.MimeTypes;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.util.ParsableByteArray;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.util.TimestampAdjuster;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
+import org.checkerframework.checker.nullness.qual.RequiresNonNull;
+
+/**
+ * A special purpose extractor for WebVTT content in HLS.
+ *
+ * <p>This extractor passes through non-empty WebVTT files untouched, however derives the correct
+ * sample timestamp for each by sniffing the X-TIMESTAMP-MAP header along with the start timestamp
+ * of the first cue header. Empty WebVTT files are not passed through, since it's not possible to
+ * derive a sample timestamp in this case.
+ */
+public final class WebvttExtractor implements Extractor {
+
+  private static final Pattern LOCAL_TIMESTAMP = Pattern.compile("LOCAL:([^,]+)");
+  private static final Pattern MEDIA_TIMESTAMP = Pattern.compile("MPEGTS:(-?\\d+)");
+  private static final int HEADER_MIN_LENGTH = 6 /* "WEBVTT" */;
+  private static final int HEADER_MAX_LENGTH = 3 /* optional Byte Order Mark */ + HEADER_MIN_LENGTH;
+
+  @Nullable private final String language;
+  private final TimestampAdjuster timestampAdjuster;
+  private final ParsableByteArray sampleDataWrapper;
+
+  private @MonotonicNonNull ExtractorOutput output;
+
+  private byte[] sampleData;
+  private int sampleSize;
+
+  public WebvttExtractor(@Nullable String language, TimestampAdjuster timestampAdjuster) {
+    this.language = language;
+    this.timestampAdjuster = timestampAdjuster;
+    this.sampleDataWrapper = new ParsableByteArray();
+    sampleData = new byte[1024];
+  }
+
+  // Extractor implementation.
+
+  @Override
+  public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
+    // Check whether there is a header without BOM.
+    input.peekFully(
+        sampleData, /* offset= */ 0, /* length= */ HEADER_MIN_LENGTH, /* allowEndOfInput= */ false);
+    sampleDataWrapper.reset(sampleData, HEADER_MIN_LENGTH);
+    if (WebvttParserUtil.isWebvttHeaderLine(sampleDataWrapper)) {
+      return true;
+    }
+    // The header did not match, try including the BOM.
+    input.peekFully(
+        sampleData,
+        /* offset= */ HEADER_MIN_LENGTH,
+        HEADER_MAX_LENGTH - HEADER_MIN_LENGTH,
+        /* allowEndOfInput= */ false);
+    sampleDataWrapper.reset(sampleData, HEADER_MAX_LENGTH);
+    return WebvttParserUtil.isWebvttHeaderLine(sampleDataWrapper);
+  }
+
+  @Override
+  public void init(ExtractorOutput output) {
+    this.output = output;
+    output.seekMap(new SeekMap.Unseekable(C.TIME_UNSET));
+  }
+
+  @Override
+  public void seek(long position, long timeUs) {
+    // This extractor is only used for the HLS use case, which should not call this method.
+    throw new IllegalStateException();
+  }
+
+  @Override
+  public void release() {
+    // Do nothing
+  }
+
+  @Override
+  public int read(ExtractorInput input, PositionHolder seekPosition)
+      throws IOException, InterruptedException {
+    // output == null suggests init() hasn't been called
+    Assertions.checkNotNull(output);
+    int currentFileSize = (int) input.getLength();
+
+    // Increase the size of sampleData if necessary.
+    if (sampleSize == sampleData.length) {
+      sampleData = Arrays.copyOf(sampleData,
+          (currentFileSize != C.LENGTH_UNSET ? currentFileSize : sampleData.length) * 3 / 2);
+    }
+
+    // Consume to the input.
+    int bytesRead = input.read(sampleData, sampleSize, sampleData.length - sampleSize);
+    if (bytesRead != C.RESULT_END_OF_INPUT) {
+      sampleSize += bytesRead;
+      if (currentFileSize == C.LENGTH_UNSET || sampleSize != currentFileSize) {
+        return Extractor.RESULT_CONTINUE;
+      }
+    }
+
+    // We've reached the end of the input, which corresponds to the end of the current file.
+    processSample();
+    return Extractor.RESULT_END_OF_INPUT;
+  }
+
+  @RequiresNonNull("output")
+  private void processSample() throws ParserException {
+    ParsableByteArray webvttData = new ParsableByteArray(sampleData);
+
+    // Validate the first line of the header.
+    WebvttParserUtil.validateWebvttHeaderLine(webvttData);
+
+    // Defaults to use if the header doesn't contain an X-TIMESTAMP-MAP header.
+    long vttTimestampUs = 0;
+    long tsTimestampUs = 0;
+
+    // Parse the remainder of the header looking for X-TIMESTAMP-MAP.
+    for (String line = webvttData.readLine();
+        !TextUtils.isEmpty(line);
+        line = webvttData.readLine()) {
+      if (line.startsWith("X-TIMESTAMP-MAP")) {
+        Matcher localTimestampMatcher = LOCAL_TIMESTAMP.matcher(line);
+        if (!localTimestampMatcher.find()) {
+          throw new ParserException("X-TIMESTAMP-MAP doesn't contain local timestamp: " + line);
+        }
+        Matcher mediaTimestampMatcher = MEDIA_TIMESTAMP.matcher(line);
+        if (!mediaTimestampMatcher.find()) {
+          throw new ParserException("X-TIMESTAMP-MAP doesn't contain media timestamp: " + line);
+        }
+        vttTimestampUs = WebvttParserUtil.parseTimestampUs(localTimestampMatcher.group(1));
+        tsTimestampUs = TimestampAdjuster.ptsToUs(Long.parseLong(mediaTimestampMatcher.group(1)));
+      }
+    }
+
+    // Find the first cue header and parse the start time.
+    Matcher cueHeaderMatcher = WebvttParserUtil.findNextCueHeader(webvttData);
+    if (cueHeaderMatcher == null) {
+      // No cues found. Don't output a sample, but still output a corresponding track.
+      buildTrackOutput(0);
+      return;
+    }
+
+    long firstCueTimeUs = WebvttParserUtil.parseTimestampUs(cueHeaderMatcher.group(1));
+    long sampleTimeUs = timestampAdjuster.adjustTsTimestamp(
+        TimestampAdjuster.usToPts(firstCueTimeUs + tsTimestampUs - vttTimestampUs));
+    long subsampleOffsetUs = sampleTimeUs - firstCueTimeUs;
+    // Output the track.
+    TrackOutput trackOutput = buildTrackOutput(subsampleOffsetUs);
+    // Output the sample.
+    sampleDataWrapper.reset(sampleData, sampleSize);
+    trackOutput.sampleData(sampleDataWrapper, sampleSize);
+    trackOutput.sampleMetadata(sampleTimeUs, C.BUFFER_FLAG_KEY_FRAME, sampleSize, 0, null);
+  }
+
+  @RequiresNonNull("output")
+  private TrackOutput buildTrackOutput(long subsampleOffsetUs) {
+    TrackOutput trackOutput = output.track(0, C.TRACK_TYPE_TEXT);
+    trackOutput.format(Format.createTextSampleFormat(null, MimeTypes.TEXT_VTT, null,
+        Format.NO_VALUE, 0, language, null, subsampleOffsetUs));
+    output.endTracks();
+    return trackOutput;
+  }
+
+}