RtpMpeg4Reader.java
/*
* Copyright 2022 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.rtsp.reader;
import static androidx.media3.common.util.Assertions.checkStateNotNull;
import static androidx.media3.common.util.Util.castNonNull;
import static androidx.media3.exoplayer.rtsp.reader.RtpReaderUtils.toSampleTimeUs;
import androidx.media3.common.C;
import androidx.media3.common.util.Log;
import androidx.media3.common.util.ParsableByteArray;
import androidx.media3.common.util.UnstableApi;
import androidx.media3.common.util.Util;
import androidx.media3.exoplayer.rtsp.RtpPacket;
import androidx.media3.exoplayer.rtsp.RtpPayloadFormat;
import androidx.media3.extractor.ExtractorOutput;
import androidx.media3.extractor.TrackOutput;
import com.google.common.primitives.Bytes;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
/**
* Parses an MPEG4 byte stream carried on RTP packets, and extracts MPEG4 Access Units. Refer to
* RFC6416 for more details.
*/
@UnstableApi
/* package */ final class RtpMpeg4Reader implements RtpPayloadReader {
private static final String TAG = "RtpMpeg4Reader";
private static final int MEDIA_CLOCK_FREQUENCY = 90_000;
/** VOP (Video Object Plane) unit type. */
private static final int I_VOP = 0;
private final RtpPayloadFormat payloadFormat;
private @MonotonicNonNull TrackOutput trackOutput;
private @C.BufferFlags int bufferFlags;
/**
* First received RTP timestamp. All RTP timestamps are dimension-less, the time base is defined
* by {@link #MEDIA_CLOCK_FREQUENCY}.
*/
private long firstReceivedTimestamp;
private int previousSequenceNumber;
private long startTimeOffsetUs;
private int sampleLength;
/** Creates an instance. */
public RtpMpeg4Reader(RtpPayloadFormat payloadFormat) {
this.payloadFormat = payloadFormat;
firstReceivedTimestamp = C.TIME_UNSET;
previousSequenceNumber = C.INDEX_UNSET;
}
@Override
public void createTracks(ExtractorOutput extractorOutput, int trackId) {
trackOutput = extractorOutput.track(trackId, C.TRACK_TYPE_VIDEO);
castNonNull(trackOutput).format(payloadFormat.format);
}
@Override
public void onReceivingFirstPacket(long timestamp, int sequenceNumber) {}
@Override
public void consume(
ParsableByteArray data, long timestamp, int sequenceNumber, boolean rtpMarker) {
checkStateNotNull(trackOutput);
// Check that this packet is in the sequence of the previous packet.
if (previousSequenceNumber != C.INDEX_UNSET) {
int expectedSequenceNumber = RtpPacket.getNextSequenceNumber(previousSequenceNumber);
if (sequenceNumber != expectedSequenceNumber) {
Log.w(
TAG,
Util.formatInvariant(
"Received RTP packet with unexpected sequence number. Expected: %d; received: %d."
+ " Dropping packet.",
expectedSequenceNumber, sequenceNumber));
}
}
// Parse VOP Type and get the buffer flags
int limit = data.bytesLeft();
trackOutput.sampleData(data, limit);
if (sampleLength == 0) {
bufferFlags = getBufferFlagsFromVop(data);
}
sampleLength += limit;
// RTP marker indicates the last packet carrying a VOP.
if (rtpMarker) {
if (firstReceivedTimestamp == C.TIME_UNSET) {
firstReceivedTimestamp = timestamp;
}
long timeUs =
toSampleTimeUs(
startTimeOffsetUs, timestamp, firstReceivedTimestamp, MEDIA_CLOCK_FREQUENCY);
trackOutput.sampleMetadata(timeUs, bufferFlags, sampleLength, 0, null);
sampleLength = 0;
}
previousSequenceNumber = sequenceNumber;
}
@Override
public void seek(long nextRtpTimestamp, long timeUs) {
firstReceivedTimestamp = nextRtpTimestamp;
startTimeOffsetUs = timeUs;
sampleLength = 0;
}
// Internal methods.
/**
* Returns VOP (Video Object Plane) Coding type.
*
* <p>Sets {@link #bufferFlags} according to the VOP Coding type.
*/
private static @C.BufferFlags int getBufferFlagsFromVop(ParsableByteArray data) {
// search for VOP_START_CODE (00 00 01 B6)
byte[] inputData = data.getData();
byte[] startCode = new byte[] {0x0, 0x0, 0x1, (byte) 0xB6};
int vopStartCodePos = Bytes.indexOf(inputData, startCode);
if (vopStartCodePos != -1) {
data.setPosition(vopStartCodePos + 4);
int vopType = data.peekUnsignedByte() >> 6;
return vopType == I_VOP ? C.BUFFER_FLAG_KEY_FRAME : 0;
}
return 0;
}
}