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Airplay握手流程（三）

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Windows平台下Airplay接收端与IOS设备连接握手流程，主要介绍GET PARAMETER信令、RECORD信令、SET PARAMETER信令以及第二个SETUP包

GET PARAMETER

发送端请求获取音量，信令是GET PARAMETER

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GET_PARAMETER rtsp://192.168.137.1/10555496157292350542 RTSP/1.0
Content-Length: 8
Content-Type: text/parameters
CSeq: 8
DACP-ID: 1FF65A04A9252F60
Active-Remote: 2814835199
User-Agent: AirPlay/409.16

volume

接收端回应音量

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RTSP/1.0 200 OK
CSeq: 8
Server: AirTunes/220.68
Content-Type: text/parameters
Content-Length: 13

volume: 0.0

目前GET PARAMETER信令支持的参数只有volume

RECORD

发送端请求启动音频流传输。信令是RECORD

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RECORD rtsp://192.168.137.1/10555496157292350542 RTSP/1.0
CSeq: 9
DACP-ID: 1FF65A04A9252F60
Active-Remote: 2814835199
User-Agent: AirPlay/409.16


接收端回应RECORD两个字段

  • Audio-Latency：音频延迟
  • Audio-Jack-Status: 音频插孔状态
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RTSP/1.0 200 OK
CSeq: 9
Server: AirTunes/220.68
Audio-Latency: 11025
Audio-Jack-Status: connected; type=analog


SET PARAMETER

发送端请求设置音量，信令是SET PARAMETER

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SET_PARAMETER rtsp://192.168.137.1/10555496157292350542 RTSP/1.0
Content-Length: 20
Content-Type: text/parameters
CSeq: 10
DACP-ID: 1FF65A04A9252F60
Active-Remote: 2814835199
User-Agent: AirPlay/409.16

volume: -20.000000

音量值的范围是0.0 ~ -144.0

接收端返回一个空包

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RTSP/1.0 200 OK
CSeq: 10
Server: AirTunes/220.68


SETUP2

发送端发送第二个SETUP包，格式依然为bplist

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SETUP rtsp://192.168.137.1/10555496157292350542 RTSP/1.0
Content-Length: 188
Content-Type: application/x-apple-binary-plist
CSeq: 11
DACP-ID: 1FF65A04A9252F60
Active-Remote: 2814835199
User-Agent: AirPlay/409.16

bplist00ÑWstreams¡ÓTtype]timestampInfo_streamConnectionIDn¥	Ñ
TnameUSubSuÑ

UBePxTÑ
UAfPxTÑ
UBefEnÑ
UEmEnc!Ûô#àH|!/DFLOTZ]cfloux~

解析后如下

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>streams</key>
	<array>
		<dict>
			<key>type</key>
			<integer>110</integer>
			<key>timestampInfo</key>
			<array>
				<dict>
					<key>name</key>
					<string>SubSu</string>
				</dict>
				<dict>
					<key>name</key>
					<string>BePxT</string>
				</dict>
				<dict>
					<key>name</key>
					<string>AfPxT</string>
				</dict>
				<dict>
					<key>name</key>
					<string>BefEn</string>
				</dict>
				<dict>
					<key>name</key>
					<string>EmEnc</string>
				</dict>
			</array>
			<key>streamConnectionID</key>
			<integer>3646029618780522008</integer>
		</dict>
	</array>
</dict>
</plist>

raop初始化

SETUP 2包主要初始化了raop的

  • 视频缓冲区
    前面说到，SETUP 1记录了16位fairplay_ekey以及32位ecdh_secret，现在结合包中streamConnectionID可以完成初始化了
    1. sha512先后摘要16位fairplay_ekey以及32位ecdh_secret，得到64位签名sign
    2. aes初向量初始化：
      1. 拼接字符串"AirPlayStreamIV" + streamConnectionID
      2. sha512先后摘要字符串以及前16位sign
      3. sha512得到64位签名vsign_aesiv，取前16位作为aes初向量vaesiv
    3. aes密钥初始化：
      1. 拼接字符串"AirPlayStreamKey" + streamConnectionID
      2. sha512先后摘要字符串以及前16位sign
      3. sha512得到64位签名vsign_aeskey，取前16位作为aes初向量vaeskey
  • 镜像socket环境
    初始化环境并开始监听相关端口，端口由系统动态分配
  • 运输层协议
    检查http头部是否存在Transport字段，值是否取值RTP/AVP/TCP，如果没有就使用udp协议，本例使用udp

接收端回应

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RTSP/1.0 200 OK
CSeq: 11
Server: AirTunes/220.68
Content-Type: application/x-apple-binary-plist
Content-Length: 120

bplist00ÓYeventPortZtimingPortÞ
Wstreams¡Ò
	XdataPortTtypen'*249BEJL
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>eventPort</key>
	<integer>5001</integer>
	<key>timingPort</key>
	<integer>58122</integer>
	<key>streams</key>
	<array>
		<dict>
			<key>dataPort</key>
			<integer>9278</integer>
			<key>type</key>
			<integer>110</integer>
		</dict>
	</array>
</dict>
</plist>

回应开启的相关端口，格式使用bplist

镜像连接握手流程已全部走通，下面就是镜像传输流程