GB28181语音广播这块，我们依据GB/T28181-针对流程和实例代码，做过详细的描述，本次主要是探讨下，广播数据过来后，如何处理。
鉴于我们之前有非常成熟的RTMP|RTSP低延迟播放模块，语音广播数据过来后，调用startAudioPlay()，ntsOnInviteAudioBroadcastResponse()处理如下：
@Overridepublic void ntsOnInviteAudioBroadcastResponse(String sourceID, String targetID, int statusCode, PlaySessionDescription 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 = session_description_.getAudioDescription();SDPRtpMapAttribute audio_attr = null;if (audio_des != null && audio_des.getRtpMapAttributes() != null && !audio_des.getRtpMapAttributes().isEmpty() )audio_attr = audio_des.getRtpMapAttributes().get(0);if ( audio_des != null && audio_attr != null ) {lib_player_.SetRTPReceiverSSRC(rtp_receiver_handle_, audio_des.getSSRC());lib_player_.SetRTPReceiverPayloadType(rtp_receiver_handle_, audio_attr.getPayloadType(),audio_attr.getEncodingName(), 2, audio_attr.getClockRate());// 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_, 8000);// lib_player_.SetRTPReceiverAudioChannels(rtp_receiver_handle_, 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 PlaySessionDescription session_description_;public Runnable set(String source_id, String target_id, int status_code, PlaySessionDescription 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);}
startAudioPlay()初始化实例后，为了保证低延迟，拉流端设置0 buffer，处于调试方便，设置download speed回调2-5秒一次（可以看到是不是有音频数据过来），由于只需要播放音频，不需要视频，所以不要设置surface下去，然后设置拉流数据回调，需要注意的是，拉到的audio数据，不要转aac输出：
private boolean startAudioPlay() {if (player_handle_ != 0 )return false;player_handle_ = lib_player_.SmartPlayerOpen(context_);if (player_handle_ == 0)return false;lib_player_.SetSmartPlayerEventCallbackV2(player_handle_,new EventHandePlayerV2());// 缓存大小可以调整lib_player_.SmartPlayerSetBuffer(player_handle_, 0);// lib_player_.SmartPlayerSetFastStartup(player_handle_, 0);// set report download speed(默认2秒一次回调 用户可自行调整report间隔)lib_player_.SmartPlayerSetReportDownloadSpeed(player_handle_, 1, 20);lib_player_.SmartPlayerClearRtpReceivers(player_handle_);lib_player_.SmartPlayerAddRtpReceiver(player_handle_, rtp_receiver_handle_);lib_player_.SmartPlayerSetSurface(player_handle_, null);// lib_player_.SmartPlayerSetRenderScaleMode(player_handle_, 1);lib_player_.SmartPlayerSetAudioOutputType(player_handle_, 1);lib_player_.SmartPlayerSetMute(player_handle_, 0);lib_player_.SmartPlayerSetAudioVolume(player_handle_, 100);lib_player_.SmartPlayerSetExternalAudioOutput(player_handle_, new PlayerExternalPCMOutput());lib_player_.SmartPlayerSetUrl(player_handle_, "rtp://ntinternal/rtpreceiver/implemention0");if (0 != lib_player_.SmartPlayerStartPlay(player_handle_)) {lib_player_.SmartPlayerClose(player_handle_);player_handle_ = 0;Log.e(TAG, "start audio paly failed");return false;}lib_player_.SmartPlayerSetAudioDataCallback(player_handle_, new PlayerAudioDataOutput());lib_player_.SmartPlayerSetPullStreamAudioTranscodeAAC(player_handle_, 0);if (0 ==lib_player_.SmartPlayerStartPullStream(player_handle_) ) {// 启动定时器，长时间收不到音频数据，则停止播放，发送BYElast_received_audio_data_time_.set(SystemClock.elapsedRealtime());handler_.postDelayed(new AudioPlayerPCMTimer(player_handle_), AudioPlayerPCMTimer.INTERVAL_MS);}return true;}
调用StartPlay后，拿到的audio数据，塞到publisher端，做回音消除处理：
class PlayerExternalPCMOutput implements NTExternalAudioOutput {private int buffer_size_ = 0;private ByteBuffer pcm_buffer_ = null;@Overridepublic ByteBuffer getPcmByteBuffer(int size) {//Log.i("getPcmByteBuffer", "size: " + size);if(size < 1)return null;if(buffer_size_ != size) {buffer_size_ = size;pcm_buffer_ = ByteBuffer.allocateDirect(buffer_size_);}return pcm_buffer_;}public void onGetPcmFrame(int ret, int sampleRate, int channel, int sampleSize, int is_low_latency) {/*Log.i("onGetPcmFrame", "ret: " + ret + ", sampleRate: " + sampleRate + ", channel: " + channel + ", sampleSize: " + sampleSize +",is_low_latency:" + is_low_latency + " buffer_size：" + buffer_size);*/if (null == pcm_buffer_)return;pcm_buffer_.rewind();if (ret == 0 && isGB28181StreamRunning && publisherHandle != 0 )libPublisher.SmartPublisherOnFarEndPCMData(publisherHandle, pcm_buffer_, sampleRate, channel, sampleSize, is_low_latency);}}private static int align(int d, int a) { return (d + (a - 1)) & ~(a - 1); }class PlayerAudioDataOutput implements NTAudioDataCallback {private int buffer_size_ = 0;private int param_info_size_ = 0;private ByteBuffer buffer_ = null;private ByteBuffer parameter_info_ = null;@Overridepublic ByteBuffer getAudioByteBuffer(int size) {//Log.i("getAudioByteBuffer", "size: " + size);if( size < 1 ) return null;if (size <= buffer_size_ && buffer_ != null )return buffer_;buffer_size_ = align(size + 256, 16);buffer_ = ByteBuffer.allocateDirect(buffer_size_);// Log.i("getAudioByteBuffer", "size: " + size + " buffer_size:" + audio_buffer_size);return buffer_;}@Overridepublic ByteBuffer getAudioParameterInfo(int size) {//Log.i("getAudioParameterInfo", "size: " + size);if(size < 1) return null;if ( size <= param_info_size_ && parameter_info_ != null )return parameter_info_;param_info_size_ = align(size + 32, 16);parameter_info_ = ByteBuffer.allocateDirect(param_info_size_);//Log.i("getAudioParameterInfo", "size: " + size + " buffer_size:" + param_info_size);return parameter_info_;}public void onAudioDataCallback(int ret, int audio_codec_id, int sample_size, int is_key_frame, long timestamp, int sample_rate, int channel, int parameter_info_size, long reserve) {/*Log.i("onAudioDataCallback", "ret: " + ret + ", audio_codec_id: " + audio_codec_id + ", sample_size: " + sample_size + ", timestamp: " + timestamp +",sample_rate:" + sample_rate);*/last_received_audio_data_time_.set(SystemClock.elapsedRealtime());}}
如果长时间收不到数据，主动断掉音频广播：
class AudioPlayerPCMTimer implements Runnable {public static final int THRESHOLD_MS = 60*1000; // 暂时设置到1分钟public static final int INTERVAL_MS = 10*1000; // 十秒一次, 太频繁影响主线程public AudioPlayerPCMTimer(long handle) {handle_ = handle;}@Overridepublic void run() {if (0 == handle_)return;if (handle_ != player_handle_) {Log.i(TAG, "AudioPlayerPCMTimer handle changed, will stop this timer, handle:" + handle_ + " new handle:" + player_handle_);return;}long last_update_time = last_received_audio_data_time_.get();long cur_time = SystemClock.elapsedRealtime();// Log.i(TAG, "AudioPlayerPCMTimer last_update_time:" + last_update_time + " cur_time:" + cur_time);if ( (last_update_time + this.THRESHOLD_MS) > cur_time) {// 继续定时器handler_.postDelayed(new AudioPlayerPCMTimer(this.handle_), this.INTERVAL_MS);// Log.i(TAG, "AudioPlayerPCMTimer running.");}else {Log.i(TAG, "AudioPlayerPCMTimer,trigger threshold, bye audio, stop player.");if (gb_broadcast_source_id_ != null && gb_broadcast_target_id_ != null) {if (gb28181_agent_ != null)gb28181_agent_.byeAudioBroadcast(gb_broadcast_source_id_, gb_broadcast_target_id_);}gb_broadcast_source_id_ = null;gb_broadcast_target_id_ = null;stopAudioPlayer();destoryRTPReceiver();btnGB28181AudioBroadcast.setText("GB28181语音广播");btnGB28181AudioBroadcast.setEnabled(false);}}private long handle_;}
停止广播数据播放：
private void stopAudioPlayer() {if (player_handle_ != 0 ) {lib_player_.SmartPlayerStopPullStream(player_handle_);lib_player_.SmartPlayerStopPlay(player_handle_);lib_player_.SmartPlayerClose(player_handle_);player_handle_ = 0;}}
销毁RTPReceiver：
private void destoryRTPReceiver() {if (rtp_receiver_handle_ != 0) {lib_player_.UnInitRTPReceiver(rtp_receiver_handle_);lib_player_.DestoryRTPReceiverSession(rtp_receiver_handle_);lib_player_.DestoryRTPReceiver(rtp_receiver_handle_);rtp_receiver_handle_ = 0;}}
以上是针对GB28181平台端音频广播播放的一点说明，感兴趣的开发者，可以酌情参考，也可以和我探讨Android平台GB28181接入模块的测试。
