Add WebVTT parser.
This commit is contained in:
Oliver Woodman
parent
525b309764
commit
4344675098
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/*
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* Copyright (C) 2014 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.android.exoplayer.text.webvtt;
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import com.google.android.exoplayer.C;
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import com.google.android.exoplayer.ParserException;
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import com.google.android.exoplayer.text.SubtitleParser;
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import com.google.android.exoplayer.util.MimeTypes;
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import java.io.BufferedReader;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.InputStreamReader;
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import java.util.ArrayList;
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import java.util.regex.Matcher;
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import java.util.regex.Pattern;
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/**
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* A simple WebVTT parser.
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* <p>
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* @see <a href="http://dev.w3.org/html5/webvtt">WebVTT specification</a>
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* <p>
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*/
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public class WebvttParser implements SubtitleParser {
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/**
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* This parser allows a custom header to be prepended to the WebVTT data, in the form of a text
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* line starting with this string.
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*
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* @hide
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*/
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public static final String EXO_HEADER = "EXO-HEADER";
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/**
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* A {@code OFFSET + value} element can be added to the custom header to specify an offset time
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* (in microseconds) that should be subtracted from the embedded MPEGTS value.
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*
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* @hide
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*/
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public static final String OFFSET = "OFFSET:";
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private static final long SAMPLING_RATE = 90;
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private static final String WEBVTT_TIMESTAMP_STRING = "(\\d+:)?[0-5]\\d:[0-5]\\d\\.\\d{3}";
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private static final Pattern WEBVTT_TIMESTAMP = Pattern.compile(WEBVTT_TIMESTAMP_STRING);
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private static final Pattern MEDIA_TIMESTAMP_OFFSET = Pattern.compile(OFFSET + "\\d+");
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private static final Pattern MEDIA_TIMESTAMP = Pattern.compile("MPEGTS:\\d+");
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@Override
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public WebvttSubtitle parse(InputStream inputStream, String inputEncoding, long startTimeUs)
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throws IOException {
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ArrayList<WebvttCue> subtitles = new ArrayList<WebvttCue>();
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long mediaTimestampUs = startTimeUs;
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long mediaTimestampOffsetUs = 0;
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BufferedReader webvttData = new BufferedReader(new InputStreamReader(inputStream, C.UTF8_NAME));
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String line;
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// file should start with "WEBVTT" on the first line or "EXO-HEADER"
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line = webvttData.readLine();
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if (line == null) {
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throw new ParserException("Expected WEBVTT or EXO-HEADER. Got null");
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}
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if (line.startsWith(EXO_HEADER)) {
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// parse the timestamp offset, if present
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Matcher matcher = MEDIA_TIMESTAMP_OFFSET.matcher(line);
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if (matcher.find()) {
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mediaTimestampOffsetUs = Long.parseLong(matcher.group().substring(7));
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}
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// read the next line, which should now be WEBVTT
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line = webvttData.readLine();
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if (line == null) {
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throw new ParserException("Expected WEBVTT. Got null");
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}
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}
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if (!line.equals("WEBVTT")) {
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throw new ParserException("Expected WEBVTT. Got " + line);
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}
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// after "WEBVTT" there should be either an empty line or an "X-TIMESTAMP-MAP" line and then
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// and empty line
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line = webvttData.readLine();
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if (!line.isEmpty()) {
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if (!line.startsWith("X-TIMESTAMP-MAP")) {
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throw new ParserException("Expected an empty line or X-TIMESTAMP-MAP. Got " + line);
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}
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// parse the media timestamp
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Matcher matcher = MEDIA_TIMESTAMP.matcher(line);
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if (!matcher.find()) {
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throw new ParserException("X-TIMESTAMP-MAP doesn't contain media timestmap: " + line);
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} else {
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mediaTimestampUs = (Long.parseLong(matcher.group().substring(7)) * 1000) / SAMPLING_RATE
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- mediaTimestampOffsetUs;
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}
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mediaTimestampUs = getAdjustedStartTime(mediaTimestampUs);
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// read in the next line (which should be an empty line)
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line = webvttData.readLine();
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}
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if (!line.isEmpty()) {
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throw new ParserException("Expected an empty line after WEBVTT or X-TIMESTAMP-MAP. Got "
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+ line);
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}
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// process the cues and text
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while ((line = webvttData.readLine()) != null) {
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// parse the cue timestamps
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Matcher matcher = WEBVTT_TIMESTAMP.matcher(line);
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long startTime;
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long endTime;
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String text = "";
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// parse start timestamp
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if (!matcher.find()) {
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throw new ParserException("Expected cue start time: " + line);
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} else {
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startTime = parseTimestampUs(matcher.group()) + mediaTimestampUs;
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}
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// parse end timestamp
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if (!matcher.find()) {
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throw new ParserException("Expected cue end time: " + line);
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} else {
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endTime = parseTimestampUs(matcher.group()) + mediaTimestampUs;
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}
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// parse text
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while (((line = webvttData.readLine()) != null) && (!line.isEmpty())) {
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text += line.trim() + "\n";
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}
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WebvttCue cue = new WebvttCue(startTime, endTime, text);
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subtitles.add(cue);
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}
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webvttData.close();
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inputStream.close();
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// copy WebvttCue data into arrays for WebvttSubtitle constructor
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String[] cueText = new String[subtitles.size()];
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long[] cueTimesUs = new long[2 * subtitles.size()];
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for (int subtitleIndex = 0; subtitleIndex < subtitles.size(); subtitleIndex++) {
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int arrayIndex = subtitleIndex * 2;
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WebvttCue cue = subtitles.get(subtitleIndex);
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cueTimesUs[arrayIndex] = cue.startTime;
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cueTimesUs[arrayIndex + 1] = cue.endTime;
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cueText[subtitleIndex] = cue.text;
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}
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WebvttSubtitle subtitle = new WebvttSubtitle(cueText, mediaTimestampUs, cueTimesUs);
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return subtitle;
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}
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@Override
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public boolean canParse(String mimeType) {
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return MimeTypes.TEXT_VTT.equals(mimeType);
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}
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protected long getAdjustedStartTime(long startTimeUs) {
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return startTimeUs;
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}
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private static long parseTimestampUs(String s) throws NumberFormatException {
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if (!s.matches(WEBVTT_TIMESTAMP_STRING)) {
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throw new NumberFormatException("has invalid format");
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}
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String[] parts = s.split("\\.", 2);
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long value = 0;
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for (String group : parts[0].split(":")) {
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value = value * 60 + Long.parseLong(group);
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}
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return (value * 1000 + Long.parseLong(parts[1])) * 1000;
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}
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private static class WebvttCue {
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public final long startTime;
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public final long endTime;
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public final String text;
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public WebvttCue(long startTime, long endTime, String text) {
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this.startTime = startTime;
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this.endTime = endTime;
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this.text = text;
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}
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}
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}
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@ -0,0 +1,93 @@
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/*
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* Copyright (C) 2014 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.android.exoplayer.text.webvtt;
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import com.google.android.exoplayer.text.Subtitle;
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import com.google.android.exoplayer.util.Assertions;
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import com.google.android.exoplayer.util.Util;
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import java.util.Arrays;
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/**
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* A representation of a WebVTT subtitle.
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*/
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public class WebvttSubtitle implements Subtitle {
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private final String[] cueText;
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private final long startTimeUs;
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private final long[] cueTimesUs;
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private final long[] sortedCueTimesUs;
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/**
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* @param cueText Text to be displayed during each cue.
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* @param startTimeUs The start time of the subtitle.
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* @param cueTimesUs Cue event times, where cueTimesUs[2 * i] and cueTimesUs[(2 * i) + 1] are
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* the start and end times, respectively, corresponding to cueText[i].
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*/
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public WebvttSubtitle(String[] cueText, long startTimeUs, long[] cueTimesUs) {
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this.cueText = cueText;
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this.startTimeUs = startTimeUs;
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this.cueTimesUs = cueTimesUs;
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this.sortedCueTimesUs = Arrays.copyOf(cueTimesUs, cueTimesUs.length);
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Arrays.sort(sortedCueTimesUs);
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}
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@Override
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public long getStartTime() {
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return startTimeUs;
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}
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@Override
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public int getNextEventTimeIndex(long timeUs) {
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Assertions.checkArgument(timeUs >= 0);
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int index = Util.binarySearchCeil(sortedCueTimesUs, timeUs, false, false);
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return index < sortedCueTimesUs.length ? index : -1;
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}
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@Override
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public int getEventTimeCount() {
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return sortedCueTimesUs.length;
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}
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@Override
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public long getEventTime(int index) {
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Assertions.checkArgument(index >= 0);
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Assertions.checkArgument(index < sortedCueTimesUs.length);
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return sortedCueTimesUs[index];
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}
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@Override
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public long getLastEventTime() {
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if (getEventTimeCount() == 0) {
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return -1;
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}
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return sortedCueTimesUs[sortedCueTimesUs.length - 1];
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}
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@Override
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public String getText(long timeUs) {
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StringBuilder subtitleStringBuilder = new StringBuilder();
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for (int i = 0; i < cueTimesUs.length; i += 2) {
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if ((cueTimesUs[i] <= timeUs) && (timeUs < cueTimesUs[i + 1])) {
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subtitleStringBuilder.append(cueText[i / 2]);
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}
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}
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return (subtitleStringBuilder.length() > 0) ? subtitleStringBuilder.toString() : null;
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}
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}
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