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/*
* Copyright (C) 2018 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.extractor.mp3;
import android.util.Pair;
import org.mozilla.thirdparty.com.google.android.exoplayer2.C;
import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.SeekPoint;
import org.mozilla.thirdparty.com.google.android.exoplayer2.metadata.id3.MlltFrame;
import org.mozilla.thirdparty.com.google.android.exoplayer2.util.Util;
/** MP3 seeker that uses metadata from an {@link MlltFrame}. */
/* package */ final class MlltSeeker implements Seeker {
/**
* Returns an {@link MlltSeeker} for seeking in the stream.
*
* @param firstFramePosition The position of the start of the first frame in the stream.
* @param mlltFrame The MLLT frame with seeking metadata.
* @return An {@link MlltSeeker} for seeking in the stream.
*/
public static MlltSeeker create(long firstFramePosition, MlltFrame mlltFrame) {
int referenceCount = mlltFrame.bytesDeviations.length;
long[] referencePositions = new long[1 + referenceCount];
long[] referenceTimesMs = new long[1 + referenceCount];
referencePositions[0] = firstFramePosition;
referenceTimesMs[0] = 0;
long position = firstFramePosition;
long timeMs = 0;
for (int i = 1; i <= referenceCount; i++) {
position += mlltFrame.bytesBetweenReference + mlltFrame.bytesDeviations[i - 1];
timeMs += mlltFrame.millisecondsBetweenReference + mlltFrame.millisecondsDeviations[i - 1];
referencePositions[i] = position;
referenceTimesMs[i] = timeMs;
}
return new MlltSeeker(referencePositions, referenceTimesMs);
}
private final long[] referencePositions;
private final long[] referenceTimesMs;
private final long durationUs;
private MlltSeeker(long[] referencePositions, long[] referenceTimesMs) {
this.referencePositions = referencePositions;
this.referenceTimesMs = referenceTimesMs;
// Use the last reference point as the duration, as extrapolating variable bitrate at the end of
// the stream may give a large error.
durationUs = C.msToUs(referenceTimesMs[referenceTimesMs.length - 1]);
}
@Override
public boolean isSeekable() {
return true;
}
@Override
public SeekPoints getSeekPoints(long timeUs) {
timeUs = Util.constrainValue(timeUs, 0, durationUs);
Pair<Long, Long> timeMsAndPosition =
linearlyInterpolate(C.usToMs(timeUs), referenceTimesMs, referencePositions);
timeUs = C.msToUs(timeMsAndPosition.first);
long position = timeMsAndPosition.second;
return new SeekPoints(new SeekPoint(timeUs, position));
}
@Override
public long getTimeUs(long position) {
Pair<Long, Long> positionAndTimeMs =
linearlyInterpolate(position, referencePositions, referenceTimesMs);
return C.msToUs(positionAndTimeMs.second);
}
@Override
public long getDurationUs() {
return durationUs;
}
/**
* Given a set of reference points as coordinates in {@code xReferences} and {@code yReferences}
* and an x-axis value, linearly interpolates between corresponding reference points to give a
* y-axis value.
*
* @param x The x-axis value for which a y-axis value is needed.
* @param xReferences x coordinates of reference points.
* @param yReferences y coordinates of reference points.
* @return The linearly interpolated y-axis value.
*/
private static Pair<Long, Long> linearlyInterpolate(
long x, long[] xReferences, long[] yReferences) {
int previousReferenceIndex =
Util.binarySearchFloor(xReferences, x, /* inclusive= */ true, /* stayInBounds= */ true);
long xPreviousReference = xReferences[previousReferenceIndex];
long yPreviousReference = yReferences[previousReferenceIndex];
int nextReferenceIndex = previousReferenceIndex + 1;
if (nextReferenceIndex == xReferences.length) {
return Pair.create(xPreviousReference, yPreviousReference);
} else {
long xNextReference = xReferences[nextReferenceIndex];
long yNextReference = yReferences[nextReferenceIndex];
double proportion =
xNextReference == xPreviousReference
? 0.0
: ((double) x - xPreviousReference) / (xNextReference - xPreviousReference);
long y = (long) (proportion * (yNextReference - yPreviousReference)) + yPreviousReference;
return Pair.create(x, y);
}
}
@Override
public long getDataEndPosition() {
return C.POSITION_UNSET;
}
}
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