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？

MESSAGE sip:34020000002000000001@192.168.2.120:15060 SIP/2.0
Call-ID: 5ae7cfcd8b6696b02a512e32c38bbe35@192.168.43.177
CSeq: 5796113 MESSAGE
From: ;tag=acc504a0
To: 
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

Broadcast
1
34020000001380000001
OK

我：是的，我需要咖啡。

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: ;tag=acc504a0
To: ;tag=1678330894580
Call-ID: 5ae7cfcd8b6696b02a512e32c38bbe35@192.168.43.177
CSeq: 5796113 MESSAGE
Content-Length: 0
Contact: 
User-Agent: GoSIP

我：能给我杯卡布基诺吗？

INVITE sip:31010400001360000001@3101040000 SIP/2.0
Call-ID: 33a3b4d751e1bf831f9d7ddd03218fcaf
CSeq: 796255 INVITE
From: ;tag=f2f8e526
To: 
Via: SIP/2.0/UDP 192.168.43.177:5060;rport;branch=z9hG4bK-353834-b98838ae9494d94a9e3acb10c1dbc8ad
Max-Forwards: 70
Contact: 
Subject: 31010400001360000001:0104001939,34020000001380000001:0
User-Agent: Daniusdk GB UserAgent V1.9-20221027
Content-Type: APPLICATION/SDP
Content-Length: 209v=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。

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: ;tag=f2f8e526
To: ;tag=1678330894725
Call-ID: 33a3b4d751e1bf831f9d7ddd03218fcaf
CSeq: 796255 INVITE
Content-Length: 208
Contact: 
Content-Type: application/sdp
Allow: INVITE, ACK, CANCEL, REGISTER, MESSAGE, NOTIFY
User-Agent: GoSIPv=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。

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: ;tag=f2f8e526
To: ;tag=1678330894725
Max-Forwards: 70
Contact: 
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：

//Author: daniusdk.com
@Override
public void ntsOnInviteAudioBroadcastResponse(String sourceID, String targetID, int statusCode, SessionDescription sessionDescription) {handler_.postDelayed(new Runnable() {@Overridepublic 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 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。