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/*
* 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;
}
}
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