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Support seeking based on MLLT metadata
Issue: #3241 ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=217252254
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library/core/src/main/java/com/google/android/exoplayer2/extractor/mp3/MlltSeeker.java
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,121 @@ | ||
| /* | ||
| * 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 com.google.android.exoplayer2.extractor.mp3; | ||
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| import android.util.Pair; | ||
| import com.google.android.exoplayer2.C; | ||
| import com.google.android.exoplayer2.extractor.SeekPoint; | ||
| import com.google.android.exoplayer2.metadata.id3.MlltFrame; | ||
| import com.google.android.exoplayer2.util.Util; | ||
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| /** MP3 seeker that uses metadata from an {@link MlltFrame}. */ | ||
| /* package */ final class MlltSeeker implements Mp3Extractor.Seeker { | ||
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| /** | ||
| * 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); | ||
| } | ||
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| private final long[] referencePositions; | ||
| private final long[] referenceTimesMs; | ||
| private final long durationUs; | ||
|
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| 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]); | ||
| } | ||
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| @Override | ||
| public boolean isSeekable() { | ||
| return true; | ||
| } | ||
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| @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)); | ||
| } | ||
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| @Override | ||
| public long getTimeUs(long position) { | ||
| Pair<Long, Long> positionAndTimeMs = | ||
| linearlyInterpolate(position, referencePositions, referenceTimesMs); | ||
| return C.msToUs(positionAndTimeMs.second); | ||
| } | ||
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| @Override | ||
| public long getDurationUs() { | ||
| return durationUs; | ||
| } | ||
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| /** | ||
| * 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); | ||
| } | ||
| } | ||
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|
||
| } |
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