C2Mp3TimestampTracker.java
/*
* Copyright (C) 2020 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.exoplayer.mediacodec;
import static java.lang.Math.max;
import androidx.media3.common.C;
import androidx.media3.common.Format;
import androidx.media3.common.util.Assertions;
import androidx.media3.common.util.Log;
import androidx.media3.decoder.DecoderInputBuffer;
import androidx.media3.extractor.MpegAudioUtil;
import java.nio.ByteBuffer;
/**
* Tracks the number of processed samples to calculate an accurate current timestamp, matching the
* calculations made in the Codec2 Mp3 decoder.
*/
/* package */ final class C2Mp3TimestampTracker {
private static final long DECODER_DELAY_FRAMES = 529;
private static final String TAG = "C2Mp3TimestampTracker";
private long anchorTimestampUs;
private long processedFrames;
private boolean seenInvalidMpegAudioHeader;
/**
* Resets the timestamp tracker.
*
* <p>This should be done when the codec is flushed.
*/
public void reset() {
anchorTimestampUs = 0;
processedFrames = 0;
seenInvalidMpegAudioHeader = false;
}
/**
* Updates the tracker with the given input buffer and returns the expected output timestamp.
*
* @param format The format associated with the buffer.
* @param buffer The current input buffer.
* @return The expected output presentation time, in microseconds.
*/
public long updateAndGetPresentationTimeUs(Format format, DecoderInputBuffer buffer) {
if (processedFrames == 0) {
anchorTimestampUs = buffer.timeUs;
}
if (seenInvalidMpegAudioHeader) {
return buffer.timeUs;
}
ByteBuffer data = Assertions.checkNotNull(buffer.data);
int sampleHeaderData = 0;
for (int i = 0; i < 4; i++) {
sampleHeaderData <<= 8;
sampleHeaderData |= data.get(i) & 0xFF;
}
int frameCount = MpegAudioUtil.parseMpegAudioFrameSampleCount(sampleHeaderData);
if (frameCount == C.LENGTH_UNSET) {
seenInvalidMpegAudioHeader = true;
processedFrames = 0;
anchorTimestampUs = buffer.timeUs;
Log.w(TAG, "MPEG audio header is invalid.");
return buffer.timeUs;
}
long currentBufferTimestampUs = getBufferTimestampUs(format.sampleRate);
processedFrames += frameCount;
return currentBufferTimestampUs;
}
/**
* Returns the timestamp of the last buffer that will be produced if the stream ends at the
* current position, in microseconds.
*
* @param format The format associated with input buffers.
* @return The timestamp of the last buffer that will be produced if the stream ends at the
* current position, in microseconds.
*/
public long getLastOutputBufferPresentationTimeUs(Format format) {
return getBufferTimestampUs(format.sampleRate);
}
private long getBufferTimestampUs(long sampleRate) {
// This calculation matches the timestamp calculation in the Codec2 Mp3 Decoder.
// https://cs.android.com/android/platform/superproject/+/main:frameworks/av/media/codec2/components/mp3/C2SoftMp3Dec.cpp;l=464;drc=ed134640332fea70ca4b05694289d91a5265bb46
return anchorTimestampUs
+ max(0, (processedFrames - DECODER_DELAY_FRAMES) * C.MICROS_PER_SECOND / sampleRate);
}
}