Cea608Decoder.java
/*
* 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 androidx.media3.extractor.text.cea;
import static androidx.media3.common.util.Assertions.checkNotNull;
import androidx.annotation.Nullable;
import androidx.media3.common.C;
import androidx.media3.common.Format;
import androidx.media3.common.util.UnstableApi;
import androidx.media3.extractor.text.CuesWithTiming;
import androidx.media3.extractor.text.CuesWithTimingSubtitle;
import androidx.media3.extractor.text.Subtitle;
import androidx.media3.extractor.text.SubtitleDecoder;
import androidx.media3.extractor.text.SubtitleDecoderException;
import androidx.media3.extractor.text.SubtitleInputBuffer;
import androidx.media3.extractor.text.SubtitleOutputBuffer;
import androidx.media3.extractor.text.SubtitleParser.OutputOptions;
import com.google.common.collect.ImmutableList;
import java.nio.ByteBuffer;
/** A {@link SubtitleDecoder} for CEA-608 (also known as "line 21 captions" and "EIA-608"). */
@UnstableApi
public final class Cea608Decoder extends CeaDecoder {
private static final CuesWithTiming EMPTY_CUES =
new CuesWithTiming(
ImmutableList.of(), /* startTimeUs= */ C.TIME_UNSET, /* durationUs= */ C.TIME_UNSET);
private final Cea608Parser cea608Parser;
@Nullable private CuesWithTiming cues;
private boolean isNewSubtitleDataAvailable;
private long lastCueUpdateUs;
/**
* Constructs an instance.
*
* @param parser A {@link Cea608Parser} to parse the subtitle data.
*/
public Cea608Decoder(Cea608Parser parser) {
this.cea608Parser = parser;
lastCueUpdateUs = C.TIME_UNSET;
}
@Override
public String getName() {
return "Cea608Decoder";
}
@Override
public void flush() {
super.flush();
isNewSubtitleDataAvailable = false;
cues = null;
cea608Parser.reset();
}
@Override
public void release() {
// Do nothing
}
@Nullable
@Override
public SubtitleOutputBuffer dequeueOutputBuffer() throws SubtitleDecoderException {
SubtitleOutputBuffer outputBuffer = super.dequeueOutputBuffer();
if (outputBuffer != null) {
return outputBuffer;
}
if (shouldClearStuckCaptions()) {
outputBuffer = getAvailableOutputBuffer();
if (outputBuffer != null) {
cues = EMPTY_CUES;
lastCueUpdateUs = C.TIME_UNSET;
Subtitle subtitle = createSubtitle();
outputBuffer.setContent(getPositionUs(), subtitle, Format.OFFSET_SAMPLE_RELATIVE);
return outputBuffer;
}
}
return null;
}
@Override
protected boolean isNewSubtitleDataAvailable() {
return isNewSubtitleDataAvailable;
}
@Override
protected Subtitle createSubtitle() {
isNewSubtitleDataAvailable = false;
return new CuesWithTimingSubtitle(ImmutableList.of(checkNotNull(cues)));
}
@SuppressWarnings("ByteBufferBackingArray")
@Override
protected void decode(SubtitleInputBuffer inputBuffer) {
ByteBuffer subtitleData = checkNotNull(inputBuffer.data);
cea608Parser.parse(
subtitleData.array(),
/* offset= */ subtitleData.arrayOffset(),
/* length= */ subtitleData.limit(),
OutputOptions.allCues(),
/* output= */ cues -> {
isNewSubtitleDataAvailable = true;
// Remove the 'stuck captions' duration - in this class the clearing of stuck captions is
// implemented by shouldClearStuckCaptions() below.
this.cues =
new CuesWithTiming(
cues.cues, /* startTimeUs= */ C.TIME_UNSET, /* durationUs= */ C.TIME_UNSET);
});
}
/** See ANSI/CTA-608-E R-2014 Annex C.9 for Caption Erase Logic. */
private boolean shouldClearStuckCaptions() {
if (cea608Parser.validDataChannelTimeoutUs == C.TIME_UNSET || lastCueUpdateUs == C.TIME_UNSET) {
return false;
}
long elapsedUs = getPositionUs() - lastCueUpdateUs;
return elapsedUs >= cea608Parser.validDataChannelTimeoutUs;
}
}