技术背景
对接Android平台GB28181设备接入端语音广播的时候，我们有遇到过INVITE SDP需要PCMA格式的audio，对方同时回了PS和PCMA两种，然后，发数据的时候，直接发了PS的。
举个不恰当的例子，就像我去星巴克跟服务员协商，我需要点一杯卡布基诺，然后服务员说，我有红茶拿铁和卡布基诺，我很高兴，结果最后妹子给我上来的是红茶拿铁。是不是很遗憾？更遗憾的是，GB28181-2016规范里面，针对语音广播PCMA格式有明确的说明和范例，并没有针对PS的描述。
场景还原
服务员：先生您好，您要点咖啡吗？
代码语言：javascript复制MESSAGE sip:34020000002000000001@192.168.2.120:15060 SIP/2.0
Call-ID: 5ae7cfcd8b6696b02a512e32c38bbe35@192.168.43.177
CSeq: 5796113 MESSAGE
From: <sip:44138091001320090001@3402000000>;tag=acc504a0
To: <sip:34020000002000000001@192.168.2.120:15060>
Via: SIP/2.0/UDP 192.168.43.177:5060;rport;branch=z9hG4bK-353834-ae5e552996a10590419bd216b81ebaa6
Max-Forwards: 70
User-Agent: Daniusdk GB UserAgent V1.9-20221027
Content-Type: Application/MANSCDP xml
Content-Length: 172
<?xml version="1.0" encoding="GB2312"?>
<Response>
<CmdType>Broadcast</CmdType>
<SN>1</SN>
<DeviceID>34020000001380000001</DeviceID>
<Result>OK</Result>
</Response>我：是的，我需要咖啡。
代码语言：javascript复制SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.168.43.177:5060;rport=5060;branch=z9hG4bK-353834-ae5e552996a10590419bd216b81ebaa6;received=192.168.225.1
From: <sip:44138091001320090001@3402000000>;tag=acc504a0
To: <sip:34020000002000000001@192.168.2.120:15060>;tag=1678330894580
Call-ID: 5ae7cfcd8b6696b02a512e32c38bbe35@192.168.43.177
CSeq: 5796113 MESSAGE
Content-Length: 0
Contact: <sip:34020000002000000001@192.168.2.120:15060>
User-Agent: GoSIP我：能给我杯卡布基诺吗？
代码语言：javascript复制INVITE sip:31010400001360000001@3101040000 SIP/2.0
Call-ID: 33a3b4d751e1bf831f9d7ddd03218fcaf
CSeq: 796255 INVITE
From: <sip:44138091001320090001@3402000000>;tag=f2f8e526
To: <sip:31010400001360000001@3101040000>
Via: SIP/2.0/UDP 192.168.43.177:5060;rport;branch=z9hG4bK-353834-b98838ae9494d94a9e3acb10c1dbc8ad
Max-Forwards: 70
Contact: <sip:44138091001320090001@192.168.43.177:5060>
Subject: 31010400001360000001:0104001939,34020000001380000001:0
User-Agent: aniusdk GB UserAgent V1.9-20221027
Content-Type: APPLICATION/SDP
Content-Length: 209
v=0
o=44138091001320090001 3887319688604 3887319688604 IN IP4 192.168.43.177
s=Play
c=IN IP4 192.168.43.177
t=0 0
m=audio 52428 RTP/AVP 8
a=recvonly
a=rtpmap:8 PCMA/8000
y=0104001939
f=v/////a/1/8/1服务员：先生您好，我们这边有红茶拿铁和卡布基诺。
代码语言：javascript复制SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.168.43.177:5060;rport=5060;branch=z9hG4bK-353834-b98838ae9494d94a9e3acb10c1dbc8ad;received=192.168.225.1
From: <sip:44138091001320090001@3402000000>;tag=f2f8e526
To: <sip:31010400001360000001@3101040000>;tag=1678330894725
Call-ID: 33a3b4d751e1bf831f9d7ddd03218fcaf
CSeq: 796255 INVITE
Content-Length: 208
Contact: <sip:34020000002000000001@192.168.2.120:15060>
Content-Type: application/sdp
Allow: INVITE, ACK, CANCEL, REGISTER, MESSAGE, NOTIFY
User-Agent: GoSIP
v=2
o=34020000002000000001 0 0 IN IP4 192.168.2.120
s=Play
c=IN IP4 192.168.2.120
t=0 0
m=audio 15082 RTP/AVP 96 8
a=sendonly
a=rtpmap:96 PS/90000
a=rtpmap:8 PCMA/8000
y=0104001939
f=v/////a/1/8/1我：好的，那太棒了。
代码语言：javascript复制ACK sip:34020000002000000001@192.168.2.120:15060 SIP/2.0
Call-ID: 33a3b4d751e1bf831f9d7ddd03218fcaf
CSeq: 796255 ACK
Via: SIP/2.0/UDP 192.168.43.177:5060;rport;branch=z9hG4bK-353834-b01972a6eaad0137b0bca192d6388540
From: <sip:44138091001320090001@3402000000>;tag=f2f8e526
To: <sip:31010400001360000001@3101040000>;tag=1678330894725
Max-Forwards: 70
Contact: <sip:44138091001320090001@192.168.43.177:5060>
User-Agent: Daniusdk GB UserAgent V1.9-20221027
Content-Length: 0咖啡上来了。。
我：怎么给我上的是红茶拿铁？明明我们协商的时候，我要的是卡布基诺！
你能有什么办法？
遇到这种情况，要么push厂商调整，既然SDP回的有PCMA格式，那就直接发送PCMA的语音广播数据，要么只能我们这边兼容，就像明明不喜欢红茶拿铁，还是要耐着性子喝。
规范回顾
说了这么多废话，还是回顾下语音广播的交互流程，因为之前的blog做过几次说明，这里不再赘述：
技术实现
本文以大牛直播SDK的Android平台基于Camera2的采集demo为例，如果需要注册到GB28181平台，点击页面的“启动GB28181”即可，有语音广播过来后，使能“GB28181语音广播”按钮，用于主动关闭语音广播之用。
其他处理不再赘述，这里说说invite audio broadcast response里面的处理：
代码语言：javascript复制//Author: daniusdk.com
@Override
public void ntsOnInviteAudioBroadcastResponse(String sourceID, String targetID, int statusCode, SessionDescription sessionDescription) {
handler_.postDelayed(new Runnable() {
@Override
public void run() {
Log.i(TAG, "ntsOnInviteAudioBroadcastResponse, statusCode:" status_code_ " sourceID:" source_id_ ", targetID:" target_id_);
boolean is_need_destory_rtp = true;
if (gb28181_agent_ != null ) {
boolean is_need_bye = 200==status_code_;
if (200 == status_code_ && session_description_ != null && rtp_receiver_handle_ != 0 ) {
MediaSessionDescription audio_des = null;
SDPRtpMapAttribute audio_attr = null;
Vector<MediaSessionDescription> audio_des_list = session_description_.getAudioDescriptions();
if (audio_des_list != null && !audio_des_list.isEmpty() ) {
for (MediaSessionDescription m : audio_des_list) {
if (m != null && m.isValidAddressType() && m.isHasAddress() && m.isHasRtpMapAttribute()) {
audio_des = m;
audio_attr = audio_des.getRtpMapAttributes().get(0);
break;
}
}
}
if ( audio_des != null && audio_attr != null ) {
lib_player_.SetRTPReceiverSSRC(rtp_receiver_handle_, audio_des.getSSRC());
int payload_type = audio_attr.getPayloadType();
String encoding_name = audio_attr.getEncodingName();
lib_player_.SetRTPReceiverPayloadType(rtp_receiver_handle_, payload_type,
encoding_name, 2, audio_attr.getClockRate());
if (encoding_name != null && encoding_name.equals("PS")) {
// 分析PS流，需要设置下面的特殊值
// 如果是90000的话，不需要设置
// lib_player_.SetRTPReceiverPSClockFrequency(rtp_receiver_handle_, payload_type, 1000);
// 含义请看28181文档, 如果PS流中有PSM的话，不需要设置
// lib_player_.SetRTPReceiverPSMap(rtp_receiver_handle_, payload_type, 0x90, 0xC0);
}
// 如果是PCMA, SDK会默认填 采样率8000, 通道1, 其他音频编码需要手动填入
//lib_player_.SetRTPReceiverAudioSamplingRate(rtp_receiver_handle_, payload_type, 8000);
//lib_player_.SetRTPReceiverAudioChannels(rtp_receiver_handle_, payload_type, 1);
lib_player_.SetRTPReceiverRemoteAddress(rtp_receiver_handle_, audio_des.getAddress(), audio_des.getPort());
lib_player_.InitRTPReceiver(rtp_receiver_handle_);
if (startAudioPlay()) {
is_need_bye = false;
is_need_destory_rtp = false;
gb_broadcast_source_id_ = source_id_;
gb_broadcast_target_id_ = target_id_;
btnGB28181AudioBroadcast.setText("终止GB28181语音广播");
btnGB28181AudioBroadcast.setEnabled(true);
}
}
} else {
btnGB28181AudioBroadcast.setText("GB28181语音广播");
}
if (is_need_bye)
gb28181_agent_.byeAudioBroadcast(source_id_, target_id_);
}
if (is_need_destory_rtp)
destoryRTPReceiver();
}
private String source_id_;
private String target_id_;
private int status_code_;
private SessionDescription session_description_;
public Runnable set(String source_id, String target_id, int status_code, SessionDescription session_description) {
this.source_id_ = source_id;
this.target_id_ = target_id;
this.status_code_ = status_code;
this.session_description_ = session_description;
return this;
}
}.set(sourceID, targetID, statusCode, sessionDescription),0);
}我们根据回上来的SDP，判断encoding_name是PCMA还是PS的，如果是PS的，可选设置下SetRTPReceiverPSClockFrequency()和SetRTPReceiverPSMap()。如果是PCMA的，还是按照老的逻辑处理即可。
总结
GB28181设备接入这块，遇到的国标平台侧的问题真的是五花八门，真是印证了那句话：GB28181相关的模块，做demo容易，做产品，真的太难了，怪不得这么多公司懒得搞这块。
