iOS Airplay--Airtunes音乐播放在Android盒子和手机上的实现 （终结篇）
16lz
2021-12-04
在上一篇，我们让iOS设备通过AirTunes连接上了Android设备链接。
这一篇，我们将完成iOS设备通过AirTunes把音乐推给Android设播放。
四、实现Android设备播放AirTunes音乐
- 1 对RaopRtsPipelineFactory的pipeline 构造完整的handler处理，新增了一个最核心的handler--RaopAudioHandler。
public class RaopRtsPipelineFactory implements ChannelPipelineFactory { @Override public ChannelPipeline getPipeline() throws Exception { final ChannelPipeline pipeline = Channels.pipeline(); //因为是管道 注意保持正确的顺序 //构造executionHanlder 和关闭executionHanlder final AirTunesRunnable airTunesRunnable = AirTunesRunnable.getInstance(); pipeline.addLast("exectionHandler", airTunesRunnable.getChannelExecutionHandler()); pipeline.addLast("closeOnShutdownHandler", new SimpleChannelUpstreamHandler(){ @Override public void channelOpen(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception { airTunesRunnable.getChannelGroup().add(e.getChannel()); super.channelOpen(ctx, e); } }); //add exception logger pipeline.addLast("exceptionLogger", new ExceptionLoggingHandler()); //rtsp decoder & encoder pipeline.addLast("decoder", new RtspRequestDecoder()); pipeline.addLast("encoder", new RtspResponseEncoder()); //rstp logger and errer response pipeline.addLast("logger", new RtspLoggingHandler()); pipeline.addLast("errorResponse", new RtspErrorResponseHandler()); //app airtunes need pipeline.addLast("challengeResponse", new RaopRtspChallengeResponseHandler(NetworkUtils.getInstance().getHardwareAddress())); pipeline.addLast("header", new RaopRtspHeaderHandler()); //let iOS devices know server support methods pipeline.addLast("options", new RaopRtspOptionsHandler()); //!!!Core handler audioHandler pipeline.addLast("audio", new RaopAudioHandler(airTunesRunnable.getExecutorService())); //unsupport Response pipeline.addLast("unsupportedResponse", new RtspUnsupportedResponseHandler()); return pipeline; }}- 2 RaopAudioHandler的处理流程：ANNOUNCE（标识链接，更新客户端session），SETUP（构造连接），RECORD（记录保存媒体数据），FLUSH（当airtunes中断时，清空里面的数据），TEARDOWN（关闭连接）。
@Override public void messageReceived(final ChannelHandlerContext ctx, final MessageEvent evt) throws Exception { final HttpRequest req = (HttpRequest)evt.getMessage(); final HttpMethod method = req.getMethod(); LOG.info("messageReceived : HttpMethod: " + method); if (RaopRtspMethods.ANNOUNCE.equals(method)) { announceReceived(ctx, req); return; } else if (RaopRtspMethods.SETUP.equals(method)) { setupReceived(ctx, req); return; } else if (RaopRtspMethods.RECORD.equals(method)) { recordReceived(ctx, req); return; } else if (RaopRtspMethods.FLUSH.equals(method)) { flushReceived(ctx, req); return; } else if (RaopRtspMethods.TEARDOWN.equals(method)) { teardownReceived(ctx, req); return; } else if (RaopRtspMethods.SET_PARAMETER.equals(method)) { setParameterReceived(ctx, req); return; } else if (RaopRtspMethods.GET_PARAMETER.equals(method)) { getParameterReceived(ctx, req); return; } super.messageReceived(ctx, evt); }A. AUNOUNCE处理。announce在传输的时候遵循了SDP协议。SDP协议用来描述媒体信息。AirTunes协议的样式如下：
/** * Sample sdp content: * v=0 o=iTunes 3413821438 0 IN IP4 fe80::217:f2ff:fe0f:e0f6 s=iTunes c=IN IP4 fe80::5a55:caff:fe1a:e187 t=0 0 m=audio 0 RTP/AVP 96 a=rtpmap:96 AppleLossless a=fmtp:96 352 0 16 40 10 14 2 255 0 0 44100 a=fpaeskey:RlBMWQECAQAAAAA8AAAAAPFOnNe+zWb5/n4L5KZkE2AAAAAQlDx69reTdwHF9LaNmhiRURTAbcL4brYAceAkZ49YirXm62N4 a=aesiv:5b+YZi9Ikb845BmNhaVo+Q */对协议进行解析：
//go through each line and parse the sdp parametersfor(final String line: sdp.split("\n")) { /* Split SDP line into attribute and setting */ final Matcher lineMatcher = s_pattern_sdp_line.matcher(line); if ( ! lineMatcher.matches()){ throw new ProtocolException("Cannot parse SDP line " + line); } final char attribute = lineMatcher.group(1).charAt(0); final String setting = lineMatcher.group(2); /* Handle attributes */ switch (attribute) { case 'm': /* Attribute m. Maps an audio format index to a stream */ final Matcher m_matcher = s_pattern_sdp_m.matcher(setting); if (!m_matcher.matches()) throw new ProtocolException("Cannot parse SDP " + attribute + "'s setting " + setting); audioFormatIndex = Integer.valueOf(m_matcher.group(2)); break; case 'a': LOG.info("setting: " + setting); /* Attribute a. Defines various session properties */ final Matcher a_matcher = s_pattern_sdp_a.matcher(setting); if ( ! a_matcher.matches() ){ throw new ProtocolException("Cannot parse SDP " + attribute + "'s setting " + setting); } final String key = a_matcher.group(1); final String value = a_matcher.group(2); if ("rtpmap".equals(key)) { /* Sets the decoder for an audio format index */ final Matcher a_rtpmap_matcher = s_pattern_sdp_a_rtpmap.matcher(value); if (!a_rtpmap_matcher.matches()) throw new ProtocolException("Cannot parse SDP " + attribute + "'s rtpmap entry " + value); final int formatIdx = Integer.valueOf(a_rtpmap_matcher.group(1)); final String format = a_rtpmap_matcher.group(2); if ("AppleLossless".equals(format)) alacFormatIndex = formatIdx; } else if ("fmtp".equals(key)) { /* Sets the decoding parameters for a audio format index */ final String[] parts = value.split(" "); if (parts.length > 0) descriptionFormatIndex = Integer.valueOf(parts[0]); if (parts.length > 1) formatOptions = Arrays.copyOfRange(parts, 1, parts.length); } else if ("rsaaeskey".equals(key)) { /* Sets the AES key required to decrypt the audio data. The key is * encrypted wih the AirTunes private key */ byte[] aesKeyRaw; rsaPkCS1OaepCipher.init(Cipher.DECRYPT_MODE, AirTunesCryptography.PrivateKey); aesKeyRaw = rsaPkCS1OaepCipher.doFinal(Base64.decodeUnpadded(value)); aesKey = new SecretKeySpec(aesKeyRaw, "AES"); } else if ("aesiv".equals(key)) { /* Sets the AES initialization vector */ aesIv = new IvParameterSpec(Base64.decodeUnpadded(value)); } break; default: /* Ignore */ break; }}*通过AES 解密的 秘钥 和 初始化矩阵IV 以及流的数据格式，从而初始化 ALAC Decoder *
B. SETUP处理。 SETUP就是iOS设备和我们信息交换：主要是三个 port 的信息，对应三个 channel。分别是 control port -> control channel ， timing port -> timing channel 和 server port -> audio channel ，这是三个 UDP 连接 的端口。这也是整个 Airtunes 服务结构核心部分。
- control port 是用来发送 resendTransmitRequest 的 channel，也就是当 Android 这边发现我收到的音乐流数据包中有丢失帧的时候，可以通过 control port 发送 resendTransmit 的 request 给 iOS 设备，设备收到后会将帧在 response 中补发回来。
- timing port 用来传输 Airplay 的时间同步包，同时也可以主动向 iOS 设备请求当前的时间戳来校准流的时间戳。
- server port 则是用来传输最主要的音乐流数据包。
- 对于这三个端口，我们同样建立了netty server和 pipelinefactory
协议解析：对指定几个 key 进行 response ，其中 interleaved 和 mode 返回的是固定参数， control_port 和 timing_port 在 request 中所对应的 value 是客户端的端口，而 response 中需要带上服务端的端口。同时，这两个 UDP 连接由服务端发起去连接客户端对应的端口。最后再告知客户端 server_port 的端口。
for(final String requestOption: requestOptions) { /* Split option into key and value */ final Matcher transportOption = PATTERN_TRANSPORT_OPTION.matcher(requestOption); if ( ! transportOption.matches() ){ throw new ProtocolException("Cannot parse Transport option " + requestOption); } final String key = transportOption.group(1); final String value = transportOption.group(3); if ("interleaved".equals(key)) { /* Probably means that two channels are interleaved in the stream. Included in the response options */ if ( ! "0-1".equals(value)){ throw new ProtocolException("Unsupported Transport option, interleaved must be 0-1 but was " + value); } responseOptions.add("interleaved=0-1"); } else if ("mode".equals(key)) { /* Means the we're supposed to receive audio data, not send it. Included in the response options */ if ( ! "record".equals(value)){ throw new ProtocolException("Unsupported Transport option, mode must be record but was " + value); } responseOptions.add("mode=record"); } else if ("control_port".equals(key)) { /* Port number of the client's control socket. Response includes port number of *our* control port */ final int clientControlPort = Integer.valueOf(value); controlChannel = createRtpChannel( substitutePort((InetSocketAddress)ctx.getChannel().getLocalAddress(), 53670), substitutePort((InetSocketAddress)ctx.getChannel().getRemoteAddress(), clientControlPort), RaopRtpChannelType.Control ); LOG.info("Launched RTP control service on " + controlChannel.getLocalAddress()); responseOptions.add("control_port=" + ((InetSocketAddress)controlChannel.getLocalAddress()).getPort()); } else if ("timing_port".equals(key)) { /* Port number of the client's timing socket. Response includes port number of *our* timing port */ final int clientTimingPort = Integer.valueOf(value); timingChannel = createRtpChannel( substitutePort((InetSocketAddress)ctx.getChannel().getLocalAddress(), 53669), substitutePort((InetSocketAddress)ctx.getChannel().getRemoteAddress(), clientTimingPort), RaopRtpChannelType.Timing ); LOG.info("Launched RTP timing service on " + timingChannel.getLocalAddress()); responseOptions.add("timing_port=" + ((InetSocketAddress)timingChannel.getLocalAddress()).getPort()); } else { /* Ignore unknown options */ responseOptions.add(requestOption); }}- 3 在setup执行后，整个Airtunes的通信图示**
(1)UpStream：数据进入 pipeline 之后，按照 RTP Packet 的格式进行 decode。在 Airplay 协议中，总共有如下几种
Packet Type：
TimingRequest [timing channel]
TimingResponse [timing channel]
Sync [timing channel]
RetransmitRequest [control channel]
AudioRetransmit [audio channel]
AudioTransmit [audio channel]timing channel 在 Sync 数据的同事，开启单独的线程每三秒钟执行一次 timing request，来确认本地时钟和客户端时钟的同步。control channel 每收到一个 新的 audio 数据包的时候都会 确认一次数据包的 sequence number 是否和当前的是连续的 ，如果不连续的，则将中间缺失的 number 标记为 missing 的数据包，并且向客户端发送一个 resend 的请求。当客户端发来了 AudioRetransmit 类型的数据包后，由 audio channel 接收的，control channel 只是负责将刚才标记为 missing 的 sequence number 清除掉。
这两个 channel 在发送 request 的时候，也会发回到 audio channel 的 Handler 上来，通过 audio channel 这边的 encode 之后再发送出去。
而音乐数据包，则需要经过 AES 解密，这个解密器我们已经在 ANNOUNCE 的时候初始化好了，再经过 ALACDecoder，也是在 ANNOUNCE 的时候根据获得的媒体信息初始化的音频解码器，最后在 EnqueueHandler 中决定是否进入音频输出队列。
(2)Down Stream： timing channel 和 control channel channel 负责向客户端发送具体的请求。
- 4 运行工程到Android设备上，在iOS通过AirTunes找到"RDuwan-Airtunes"，连接上设备，打开iOS上的音乐软件(比如QQ音乐)，即可以在Android设备上成功听到了音乐的播放。
- 5 完整工程见github链接
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