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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.extractor.mp3;
import androidx.annotation.Nullable;
import org.mozilla.thirdparty.com.google.android.exoplayer2.C;
import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.MpegAudioHeader;
import org.mozilla.thirdparty.com.google.android.exoplayer2.extractor.SeekPoint;
import org.mozilla.thirdparty.com.google.android.exoplayer2.util.Assertions;
import org.mozilla.thirdparty.com.google.android.exoplayer2.util.Log;
import org.mozilla.thirdparty.com.google.android.exoplayer2.util.ParsableByteArray;
import org.mozilla.thirdparty.com.google.android.exoplayer2.util.Util;
/** MP3 seeker that uses metadata from a Xing header. */
/* package */ final class XingSeeker implements Seeker {
private static final String TAG = "XingSeeker";
/**
* Returns a {@link XingSeeker} for seeking in the stream, if required information is present.
* Returns {@code null} if not. On returning, {@code frame}'s position is not specified so the
* caller should reset it.
*
* @param inputLength The length of the stream in bytes, or {@link C#LENGTH_UNSET} if unknown.
* @param position The position of the start of this frame in the stream.
* @param mpegAudioHeader The MPEG audio header associated with the frame.
* @param frame The data in this audio frame, with its position set to immediately after the
* 'Xing' or 'Info' tag.
* @return A {@link XingSeeker} for seeking in the stream, or {@code null} if the required
* information is not present.
*/
public static @Nullable XingSeeker create(
long inputLength, long position, MpegAudioHeader mpegAudioHeader, ParsableByteArray frame) {
int samplesPerFrame = mpegAudioHeader.samplesPerFrame;
int sampleRate = mpegAudioHeader.sampleRate;
int flags = frame.readInt();
int frameCount;
if ((flags & 0x01) != 0x01 || (frameCount = frame.readUnsignedIntToInt()) == 0) {
// If the frame count is missing/invalid, the header can't be used to determine the duration.
return null;
}
long durationUs = Util.scaleLargeTimestamp(frameCount, samplesPerFrame * C.MICROS_PER_SECOND,
sampleRate);
if ((flags & 0x06) != 0x06) {
// If the size in bytes or table of contents is missing, the stream is not seekable.
return new XingSeeker(position, mpegAudioHeader.frameSize, durationUs);
}
long dataSize = frame.readUnsignedIntToInt();
long[] tableOfContents = new long[100];
for (int i = 0; i < 100; i++) {
tableOfContents[i] = frame.readUnsignedByte();
}
// TODO: Handle encoder delay and padding in 3 bytes offset by xingBase + 213 bytes:
// delay = (frame.readUnsignedByte() << 4) + (frame.readUnsignedByte() >> 4);
// padding = ((frame.readUnsignedByte() & 0x0F) << 8) + frame.readUnsignedByte();
if (inputLength != C.LENGTH_UNSET && inputLength != position + dataSize) {
Log.w(TAG, "XING data size mismatch: " + inputLength + ", " + (position + dataSize));
}
return new XingSeeker(
position, mpegAudioHeader.frameSize, durationUs, dataSize, tableOfContents);
}
private final long dataStartPosition;
private final int xingFrameSize;
private final long durationUs;
/** Data size, including the XING frame. */
private final long dataSize;
private final long dataEndPosition;
/**
* Entries are in the range [0, 255], but are stored as long integers for convenience. Null if the
* table of contents was missing from the header, in which case seeking is not be supported.
*/
@Nullable private final long[] tableOfContents;
private XingSeeker(long dataStartPosition, int xingFrameSize, long durationUs) {
this(
dataStartPosition,
xingFrameSize,
durationUs,
/* dataSize= */ C.LENGTH_UNSET,
/* tableOfContents= */ null);
}
private XingSeeker(
long dataStartPosition,
int xingFrameSize,
long durationUs,
long dataSize,
@Nullable long[] tableOfContents) {
this.dataStartPosition = dataStartPosition;
this.xingFrameSize = xingFrameSize;
this.durationUs = durationUs;
this.tableOfContents = tableOfContents;
this.dataSize = dataSize;
dataEndPosition = dataSize == C.LENGTH_UNSET ? C.POSITION_UNSET : dataStartPosition + dataSize;
}
@Override
public boolean isSeekable() {
return tableOfContents != null;
}
@Override
public SeekPoints getSeekPoints(long timeUs) {
if (!isSeekable()) {
return new SeekPoints(new SeekPoint(0, dataStartPosition + xingFrameSize));
}
timeUs = Util.constrainValue(timeUs, 0, durationUs);
double percent = (timeUs * 100d) / durationUs;
double scaledPosition;
if (percent <= 0) {
scaledPosition = 0;
} else if (percent >= 100) {
scaledPosition = 256;
} else {
int prevTableIndex = (int) percent;
long[] tableOfContents = Assertions.checkNotNull(this.tableOfContents);
double prevScaledPosition = tableOfContents[prevTableIndex];
double nextScaledPosition = prevTableIndex == 99 ? 256 : tableOfContents[prevTableIndex + 1];
// Linearly interpolate between the two scaled positions.
double interpolateFraction = percent - prevTableIndex;
scaledPosition = prevScaledPosition
+ (interpolateFraction * (nextScaledPosition - prevScaledPosition));
}
long positionOffset = Math.round((scaledPosition / 256) * dataSize);
// Ensure returned positions skip the frame containing the XING header.
positionOffset = Util.constrainValue(positionOffset, xingFrameSize, dataSize - 1);
return new SeekPoints(new SeekPoint(timeUs, dataStartPosition + positionOffset));
}
@Override
public long getTimeUs(long position) {
long positionOffset = position - dataStartPosition;
if (!isSeekable() || positionOffset <= xingFrameSize) {
return 0L;
}
long[] tableOfContents = Assertions.checkNotNull(this.tableOfContents);
double scaledPosition = (positionOffset * 256d) / dataSize;
int prevTableIndex = Util.binarySearchFloor(tableOfContents, (long) scaledPosition, true, true);
long prevTimeUs = getTimeUsForTableIndex(prevTableIndex);
long prevScaledPosition = tableOfContents[prevTableIndex];
long nextTimeUs = getTimeUsForTableIndex(prevTableIndex + 1);
long nextScaledPosition = prevTableIndex == 99 ? 256 : tableOfContents[prevTableIndex + 1];
// Linearly interpolate between the two table entries.
double interpolateFraction = prevScaledPosition == nextScaledPosition ? 0
: ((scaledPosition - prevScaledPosition) / (nextScaledPosition - prevScaledPosition));
return prevTimeUs + Math.round(interpolateFraction * (nextTimeUs - prevTimeUs));
}
@Override
public long getDurationUs() {
return durationUs;
}
@Override
public long getDataEndPosition() {
return dataEndPosition;
}
/**
* Returns the time in microseconds for a given table index.
*
* @param tableIndex A table index in the range [0, 100].
* @return The corresponding time in microseconds.
*/
private long getTimeUsForTableIndex(int tableIndex) {
return (durationUs * tableIndex) / 100;
}
}
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