com.github.xingshuangs.iot.protocol.rtp.model.RtpHeader Maven / Gradle / Ivy
package com.github.xingshuangs.iot.protocol.rtp.model;
import com.github.xingshuangs.iot.protocol.common.IObjectByteArray;
import com.github.xingshuangs.iot.protocol.common.buff.ByteReadBuff;
import com.github.xingshuangs.iot.protocol.common.buff.ByteWriteBuff;
import com.github.xingshuangs.iot.utils.BooleanUtil;
import lombok.Data;
import java.util.ArrayList;
import java.util.List;
/**
* RTP数据包头
* The RTP header has the following format:
*
* 0 1 2 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* |V=2|P|X| CC |M| PT | sequence number |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | timestamp |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | synchronization source (SSRC) identifier |
* +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
* | contributing source (CSRC) identifiers |
* | .... |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*
* RTP Header Extension
* 0 1 2 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | defined by profile | length |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | header extension |
* | .... |
*
* @author xingshuang
*/
@Data
public class RtpHeader implements IObjectByteArray {
/**
* 版本（V）：2 bits RTP版本号，现在用的是
* This field identifies the version of RTP. The version defined by
* this specification is two (2). (The value 1 is used by the first
* draft version of RTP and the value 0 is used by the protocol
* initially implemented in the "vat" audio tool.)
*/
private int version;
/**
* 填充（P）：1比特，1 bit 如果设置了该字段，报文的末尾会包含一个或多个填充字节，这些填充字节不是payload的内容。
* 最后一个填充字节标识了总共需要忽略多少个填充字节（包括自己）
* If the padding bit is set, the packet contains one or more
* additional padding octets at the end which are not part of the
* payload. The last octet of the padding contains a count of how
* many padding octets should be ignored, including itself. Padding
* may be needed by some encryption algorithms with fixed block sizes
* or for carrying several RTP packets in a lower-layer protocol data
* unit.
*/
private boolean padding;
/**
* 1 bit 如果设置了该字段，那么头数据后跟着一个拓展数据
* If the extension bit is set, the fixed header MUST be followed by
* exactly one header extension
*/
private boolean extension;
/**
* CSRC Count，共享媒体源个数，一般用于混音和混屏中，例如某个音频流是混合了其它音频后的数据，那么其它音频源就是该音频源的 CSRC
* 4 bits CSRC列表的长度。
* The CSRC count contains the number of CSRC identifiers that follow
* the fixed header.
*/
private int csrcCount;
/**
* Mark 标记位，对于不同的负载类型有不同含义，例如使用 RTP 荷载 H264 码流时，如果某个帧分成多个包进行传输，可以使用该位标记是否为帧的最后一个包
* 1 bit Marker会在预设中进行定义（预设和RTP的关系可以参考rfc3551，我的理解是预设是对RTP的补充，以达到某一类实际使用场景的需要），
* 在报文流中用它来划分每一帧的边界。预设中可能会定义附加的marker，或者移除Marker来拓展payload type字段的长度。
* The interpretation of the marker is defined by a profile. It is
* intended to allow significant events such as frame boundaries to
* be marked in the packet stream. A profile MAY define additional
* marker bits or specify that there is no marker bit by changing the
* number of bits in the payload type field
*/
private boolean marker;
/**
* 7 bits 该字段定义RTP payload的格式和他在预设中的意义。上层应用可能会定义一个（静态的类型码<->payload格式）映射关系。
* 也可以用RTP协议外的方式来动态地定义payload类型。在一个RTP session中payload类型可能会改变，但是不应该用payload类型来区分不同的媒体流，
* 正如之前所说，不同的媒体流应该通过不同session分别传输。
* This field identifies the format of the RTP payload and determines
* its interpretation by the application.
*/
private int payloadType;
/**
* 16 bits 每发送一个RTP包该序列号+1，RTP包的接受者可以通过它来确定丢包情况并且利用它来重排包的顺序。
* 这个字段的初始值应该是随机的，这会让known-plaintext更加困难。
* The sequence number increments by one for each RTP data packet
* sent, and may be used by the receiver to detect packet loss and to
* restore packet sequence.
*/
private int sequenceNumber;
/**
* 32 bits 时间戳反映了RTP数据包生成第一块数据时的时刻
* The timestamp reflects the sampling instant of the first octet in
* the RTP data packet.
*/
private long timestamp;
/**
* 32 bits 该字段用来确定数据的发送源。这个身份标识应该随机生成，并且要保证同一个RTP session中没有重复的SSRC。
* 虽然SSRC冲突的概率很小，但是每个RTP客户端都应该时刻警惕，如果发现冲突就要去解决。
* The SSRC field identifies the synchronization source.
*/
private long ssrc;
/**
* 0 ~ 15 items， 32 bits each CSRC list表示对该payload数据做出贡献的所有SSRC。
* 这个字段包含的SSRC数量由CC字段定义。如果有超过15个SSRC，只有15个可以被记录。
* The CSRC list identifies the contributing sources for the payload
* contained in this packet. The number of identifiers is given by
* the CC field. If there are more than 15 contributing sources,
* only 15 can be identified.
*/
private List csrcList = new ArrayList<>();
/**
* 扩展头Id，2个字节
*/
private int extensionHeaderId;
/**
* 扩展头长度，2个字节
*/
private int extensionHeaderLength;
/**
* 扩展头的内容
*/
private byte[] extensionHeaderContent = new byte[0];
@Override
public int byteArrayLength() {
int sum = 12 + this.csrcCount * 4;
if (this.extension) {
sum += 4 + this.extensionHeaderLength;
}
return sum;
}
@Override
public byte[] toByteArray() {
byte first = (byte) (((this.version << 6) & 0xC0)
| BooleanUtil.setBit(5, this.padding)
| BooleanUtil.setBit(4, this.extension)
| (this.csrcCount & 0x0F));
byte second = (byte) (BooleanUtil.setBit(7, this.marker) | (this.payloadType & 0x7F));
ByteWriteBuff buff = ByteWriteBuff.newInstance(this.byteArrayLength())
.putByte(first)
.putByte(second)
.putShort(this.sequenceNumber)
.putInteger(this.timestamp)
.putInteger(this.ssrc);
this.csrcList.forEach(buff::putInteger);
if (this.extension) {
buff.putShort(this.extensionHeaderId);
buff.putShort(this.extensionHeaderLength);
buff.putBytes(this.extensionHeaderContent);
}
return buff.getData();
}
/**
* 字节数组数据解析
*
* @param data 字节数组数据
* @return RtcpHeader
*/
public static RtpHeader fromBytes(final byte[] data) {
return fromBytes(data, 0);
}
/**
* 字节数组数据解析
*
* @param data 字节数组数据
* @param offset 偏移量
* @return RtcpHeader
*/
public static RtpHeader fromBytes(final byte[] data, final int offset) {
if (data.length < 12) {
throw new IndexOutOfBoundsException("解析header时，字节数组长度不够");
}
ByteReadBuff buff = new ByteReadBuff(data, offset);
RtpHeader res = new RtpHeader();
byte aByte = buff.getByte();
res.version = (aByte >> 6) & 0x03;
res.padding = BooleanUtil.getValue(aByte, 5);
res.extension = BooleanUtil.getValue(aByte, 4);
res.csrcCount = aByte & 0x0F;
byte bByte = buff.getByte();
res.marker = BooleanUtil.getValue(bByte, 7);
res.payloadType = bByte & 0x7F;
res.sequenceNumber = buff.getUInt16();
res.timestamp = buff.getUInt32();
res.ssrc = buff.getUInt32();
for (int i = 0; i < res.csrcCount; i++) {
res.csrcList.add(buff.getUInt32());
}
// 扩展头
if (res.extension) {
res.extensionHeaderId = buff.getUInt16();
res.extensionHeaderLength = buff.getUInt16() * 4;
res.extensionHeaderContent = buff.getBytes(res.extensionHeaderLength);
}
return res;
}
}