技术背景

随着智慧数字人、AI数字人的兴起，越来越多的公司着手构建​全息、真实感数字角色等技术合成的数字仿真人虚拟形象，通过“虚拟形象+语音交互（T-T-S、ASR）+自然语言理解（NLU）+深度学习”，构建适用于数字客服、虚拟展厅讲解、 智慧城市、智慧医疗、智慧教育等场景，通过人机可视化语音交互，释放人员基础劳动力，降低运营成本，提升智慧交互体验。​

​一个有“温度”的智慧数字人，有多个维度组成，如图像识别、语音识别、语义理解等，本文主要阐述的是如何把这样一个智慧数字人，通过编码传输，以更低的延迟和好的体验，呈现给用户。​

​技术实现​

​本文以Windows平台为例，从技术角度探讨智慧数字人的实时编码传输。先上图：​

左侧是Unity采集、获取video Texture和AudioClip数据，编码打包后，然后通过RTMP推送到服务端，右下侧实时拉取RTMP流数据播放，整体延迟在毫秒级。

视频采集这块，实现了Unity获取到的Texture数据的采集、摄像头采集、屏幕采集三大类：

public void SelVideoPushType(int type){switch (type){case 0:video_push_type_ = (uint)NTSmartPublisherDefine.NT_PB_E_VIDEO_OPTION.NT_PB_E_VIDEO_OPTION_LAYER;    //采集Unity窗体break;case 1:video_push_type_ = (uint)NTSmartPublisherDefine.NT_PB_E_VIDEO_OPTION.NT_PB_E_VIDEO_OPTION_CAMERA;   //采集摄像头break;case 2:video_push_type_ = (uint)NTSmartPublisherDefine.NT_PB_E_VIDEO_OPTION.NT_PB_E_VIDEO_OPTION_SCREEN;   //采集屏幕break;case 3:video_push_type_ = (uint)NTSmartPublisherDefine.NT_PB_E_VIDEO_OPTION.NT_PB_E_VIDEO_OPTION_NO_VIDEO; //不采集视频break;}Debug.Log("SelVideoPushType type: " + type + " video_push_type: " + video_push_type_);}

音频采集部分，我们主要实现了采集AudioClip的声音、麦克风、扬声器、还有两路AudioClip的音频混音：

public void SelAudioPushType(int type){switch (type){case 0:audio_push_type_ = (uint)NTSmartPublisherDefine.NT_PB_E_AUDIO_OPTION.NT_PB_E_AUDIO_OPTION_EXTERNAL_PCM_DATA;    //采集Unity声音break;case 1:audio_push_type_ = (uint)NTSmartPublisherDefine.NT_PB_E_AUDIO_OPTION.NT_PB_E_AUDIO_OPTION_CAPTURE_MIC;  //采集麦克风break;case 2:audio_push_type_ = (uint)NTSmartPublisherDefine.NT_PB_E_AUDIO_OPTION.NT_PB_E_AUDIO_OPTION_CAPTURE_SPEAKER;  //采集扬声器break;case 3:audio_push_type_ = (uint)NTSmartPublisherDefine.NT_PB_E_AUDIO_OPTION.NT_PB_E_AUDIO_OPTION_TWO_EXTERNAL_PCM_MIXER;  //两路Unity AudioClip混音break;case 4:audio_push_type_ = (uint)NTSmartPublisherDefine.NT_PB_E_AUDIO_OPTION.NT_PB_E_AUDIO_OPTION_NO_AUDIO;   //不采集音频break;}Debug.Log("SelAudioPushType type: " + type + " audio_push_type: " + audio_push_type_);}

为了便于测试延迟，在页面加了个简单的时间日期刷新：

//获取当前时间GameObject.Find("Canvas/Panel/LableText").GetComponent<Text>().text = string.Format("{0:D2}:{1:D2}:{2:D2}:{3:D2} " + "{4:D4}/{5:D2}/{6:D2}",DateTime.Now.Hour, DateTime.Now.Minute, DateTime.Now.Second, DateTime.Now.Millisecond,DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day);

Unity窗体或Camera采集，可以从Texuture拿到数据，从而获取到rgb数据，投递到封装的wrapper层，实现编码传输。

if (texture_ == null || video_width_ != Screen.width || video_height_ != Screen.height){Debug.Log("OnPostRender screen changed++ scr_width: " + Screen.width + " scr_height: " + Screen.height);if (screen_image_ != IntPtr.Zero){Marshal.FreeHGlobal(screen_image_);screen_image_ = IntPtr.Zero;}if (texture_ != null){UnityEngine.Object.Destroy(texture_);texture_ = null;}video_width_ = Screen.width;video_height_ = Screen.height;texture_ = new Texture2D(video_width_, video_height_, TextureFormat.BGRA32, false);screen_image_ = Marshal.AllocHGlobal(video_width_ * 4 * video_height_);Debug.Log("OnPostRender screen changed--");return;}texture_.ReadPixels(new Rect(0, 0, video_width_, video_height_), 0, 0, false);texture_.Apply();

摄像头和屏幕采集，可以直接在封装层实现，如果需要做预览，只需要把数据回到Unity，通过RawImage实时刷新Texture显示即可。

通过封装层实现数据预览：

public bool StartPreview(){if(CheckPublisherHandleAvailable() == false)return false;video_preview_image_callback_ = new NT_PB_SDKVideoPreviewImageCallBack(SDKVideoPreviewImageCallBack);NTSmartPublisherSDK.NT_PB_SetVideoPreviewImageCallBack(publisher_handle_, (int)NTSmartPublisherDefine.NT_PB_E_IMAGE_FORMAT.NT_PB_E_IMAGE_FORMAT_RGB32, IntPtr.Zero, video_preview_image_callback_);if (NTBaseCodeDefine.NT_ERC_OK != NTSmartPublisherSDK.NT_PB_StartPreview(publisher_handle_, 0, IntPtr.Zero)){if (0 == publisher_handle_count_){NTSmartPublisherSDK.NT_PB_Close(publisher_handle_);publisher_handle_ = IntPtr.Zero;}return false;}publisher_handle_count_++;is_previewing_ = true;return true;}public void StopPreview(){if (is_previewing_ == false) return;is_previewing_ = false;publisher_handle_count_--;NTSmartPublisherSDK.NT_PB_StopPreview(publisher_handle_);if (0 == publisher_handle_count_){NTSmartPublisherSDK.NT_PB_Close(publisher_handle_);publisher_handle_ = IntPtr.Zero;}}

预览数据回调：

//预览数据回调public void SDKVideoPreviewImageCallBack(IntPtr handle, IntPtr user_data, IntPtr image){NT_PB_Image pb_image = (NT_PB_Image)Marshal.PtrToStructure(image, typeof(NT_PB_Image));NT_VideoFrame pVideoFrame = new NT_VideoFrame();pVideoFrame.width_ = pb_image.width_;pVideoFrame.height_ = pb_image.height_;pVideoFrame.stride_ = pb_image.stride_[0];Int32 argb_size = pb_image.stride_[0] * pb_image.height_;pVideoFrame.plane_data_ = new byte[argb_size];if (argb_size > 0){Marshal.Copy(pb_image.plane_[0],pVideoFrame.plane_data_,0, argb_size);}{cur_image_ = pVideoFrame;}}

音频采集这块，Unity环境下，主要是采集Unity的AudioClip数据，这块需要注意的是，PCM数据发送间隔，每隔10毫秒发一次，因为AudioClip的size比如可能只有十几秒或者几分钟，需要考虑的是，AudioClip数据采集播放完毕后，是loop的形式反复播放，还是静音帧的形式，只传视频，不传音频。

var pcm_data = new PCMData();
pcm_data.sample_rate_ = audio_clip_info_.audio_clip_.frequency;
pcm_data.channels_ = audio_clip_info_.audio_clip_.channels;
pcm_data.per_channel_sample_number_ = pcm_data.sample_rate_ / 100;var pcm_sample = new float[pcm_data.sample_rate_ * pcm_data.channels_ / 100];audio_clip_info_.audio_clip_.GetData(pcm_sample, audio_clip_info_.audio_clip_offset_);var sample_length = sizeof(float) * pcm_sample.Length;pcm_data.data_ = Marshal.AllocHGlobal(sample_length);
Marshal.Copy(pcm_sample, 0, pcm_data.data_, pcm_sample.Length);
pcm_data.size_ = (uint)sample_length;publisher_wrapper_.OnPostAudioPCMFloatData(pcm_data.data_,pcm_data.size_,pcm_time_stamp_,pcm_data.sample_rate_,pcm_data.channels_,pcm_data.per_channel_sample_number_);Marshal.FreeHGlobal(pcm_data.data_);
pcm_data.data_ = IntPtr.Zero;
pcm_data = null;pcm_time_stamp_ += 10;  //时间戳自增10毫秒

如果要两路混音，只要再从Resources下面，获取另一路AudioClip数据，然后投递即可：

audio_clip_info_mix_ = new AudioClipInfo();
audio_clip_info_mix_.audio_clip_ = Resources.Load("AudioData/music") as AudioClip;

​数据投递，用以下接口：​

publisher_wrapper_.OnPostAudioExternalPCMFloatMixerData(pcm_data_mix.data_,pcm_data_mix.size_,pcm_time_stamp_mix_,pcm_data_mix.sample_rate_,pcm_data_mix.channels_,pcm_data_mix.per_channel_sample_number_);

数据采集投递过来后，我们以图层的形式投递过来，设置音视频编码参数，底层实现音视频编码：

/** nt_publisher_wrapper.cs* nt_publisher_wrapper* * Github: https://github.com/daniulive/SmarterStreaming* * Created by DaniuLive on 2017/11/14.*/  
private void SetCommonOptionToPublisherSDK(){if (!IsPublisherHandleAvailable()){Debug.Log("SetCommonOptionToPublisherSDK, publisher handle with null..");return;}NTSmartPublisherSDK.NT_PB_ClearLayersConfig(publisher_handle_, 0,0, IntPtr.Zero);if (video_option_ == (uint)NTSmartPublisherDefine.NT_PB_E_VIDEO_OPTION.NT_PB_E_VIDEO_OPTION_LAYER){// 第0层填充RGBA矩形, 目的是保证帧率, 颜色就填充全黑int red = 0;int green = 0;int blue = 0;int alpha = 255;NT_PB_RGBARectangleLayerConfig rgba_layer_c0 = new NT_PB_RGBARectangleLayerConfig();rgba_layer_c0.base_.type_ = (Int32)NTSmartPublisherDefine.NT_PB_E_LAYER_TYPE.NT_PB_E_LAYER_TYPE_RGBA_RECTANGLE;rgba_layer_c0.base_.index_ = 0;rgba_layer_c0.base_.enable_ = 1;rgba_layer_c0.base_.region_.x_ = 0;rgba_layer_c0.base_.region_.y_ = 0;rgba_layer_c0.base_.region_.width_ = video_width_;rgba_layer_c0.base_.region_.height_ = video_height_;rgba_layer_c0.base_.offset_ = Marshal.OffsetOf(rgba_layer_c0.GetType(), "base_").ToInt32();rgba_layer_c0.base_.cb_size_ = (uint)Marshal.SizeOf(rgba_layer_c0);rgba_layer_c0.red_ = System.BitConverter.GetBytes(red)[0];rgba_layer_c0.green_ = System.BitConverter.GetBytes(green)[0];rgba_layer_c0.blue_ = System.BitConverter.GetBytes(blue)[0];rgba_layer_c0.alpha_ = System.BitConverter.GetBytes(alpha)[0];IntPtr rgba_conf = Marshal.AllocHGlobal(Marshal.SizeOf(rgba_layer_c0));Marshal.StructureToPtr(rgba_layer_c0, rgba_conf, true);UInt32 rgba_r = NTSmartPublisherSDK.NT_PB_AddLayerConfig(publisher_handle_, 0,rgba_conf, (int)NTSmartPublisherDefine.NT_PB_E_LAYER_TYPE.NT_PB_E_LAYER_TYPE_RGBA_RECTANGLE,0, IntPtr.Zero);Marshal.FreeHGlobal(rgba_conf);NT_PB_ExternalVideoFrameLayerConfig external_layer_c1 = new NT_PB_ExternalVideoFrameLayerConfig();external_layer_c1.base_.type_ = (Int32)NTSmartPublisherDefine.NT_PB_E_LAYER_TYPE.NT_PB_E_LAYER_TYPE_EXTERNAL_VIDEO_FRAME;external_layer_c1.base_.index_ = 1;external_layer_c1.base_.enable_ = 1;external_layer_c1.base_.region_.x_ = 0;external_layer_c1.base_.region_.y_ = 0;external_layer_c1.base_.region_.width_ = video_width_;external_layer_c1.base_.region_.height_ = video_height_;external_layer_c1.base_.offset_ = Marshal.OffsetOf(external_layer_c1.GetType(), "base_").ToInt32();external_layer_c1.base_.cb_size_ = (uint)Marshal.SizeOf(external_layer_c1);IntPtr external_layer_conf = Marshal.AllocHGlobal(Marshal.SizeOf(external_layer_c1));Marshal.StructureToPtr(external_layer_c1, external_layer_conf, true);UInt32 external_r = NTSmartPublisherSDK.NT_PB_AddLayerConfig(publisher_handle_, 0,external_layer_conf, (int)NTSmartPublisherDefine.NT_PB_E_LAYER_TYPE.NT_PB_E_LAYER_TYPE_EXTERNAL_VIDEO_FRAME,0, IntPtr.Zero);Marshal.FreeHGlobal(external_layer_conf);}else if (video_option_ == (uint)NTSmartPublisherDefine.NT_PB_E_VIDEO_OPTION.NT_PB_E_VIDEO_OPTION_CAMERA){CameraInfo camera = cameras_[cur_sel_camera_index_];NT_PB_VideoCaptureCapability cap = camera.capabilities_[cur_sel_camera_resolutions_index_];SetVideoCaptureDeviceBaseParameter(camera.id_.ToString(), (UInt32)cap.width_, (UInt32)cap.height_);}SetFrameRate((uint)video_fps_);Int32 type = 0;   //软编码Int32 encoder_id = 1;UInt32 codec_id = (UInt32)NTCommonMediaDefine.NT_MEDIA_CODEC_ID.NT_MEDIA_CODEC_ID_H264;Int32 param1 = 0;SetVideoEncoder(type, encoder_id, codec_id, param1);SetVideoQualityV2(CalVideoQuality(video_width_, video_height_, is_h264_encoder_));SetVideoBitRate(CalBitRate(video_fps_, video_width_, video_height_));SetVideoMaxBitRate((CalMaxKBitRate(video_fps_, video_width_, video_height_, false)));SetVideoKeyFrameInterval((key_frame_interval_));if (is_h264_encoder_){SetVideoEncoderProfile(1);}SetVideoEncoderSpeed(CalVideoEncoderSpeed(video_width_, video_height_, is_h264_encoder_));// 音频相关设置SetAuidoInputDeviceId(0);SetPublisherAudioCodecType(1);SetPublisherMute(is_mute_);SetEchoCancellation(0, 0);SetNoiseSuppression(0);SetAGC(0);SetVAD(0);SetInputAudioVolume(Convert.ToSingle(audio_input_volume_));}

编码打包后，可以调用推送接口，把打包后的数据，实时传到RTMP服务端：

public bool StartPublisher(String url){if (CheckPublisherHandleAvailable() == false) return false;if (publisher_handle_ == IntPtr.Zero){return false;}if (!String.IsNullOrEmpty(url)){NTSmartPublisherSDK.NT_PB_SetURL(publisher_handle_, url, IntPtr.Zero);}if (NTBaseCodeDefine.NT_ERC_OK != NTSmartPublisherSDK.NT_PB_StartPublisher(publisher_handle_, IntPtr.Zero)){if (0 == publisher_handle_count_){NTSmartPublisherSDK.NT_PB_Close(publisher_handle_);publisher_handle_ = IntPtr.Zero;}is_publishing_ = false;return false;}publisher_handle_count_++;is_publishing_ = true;return true;}public void StopPublisher(){if (is_publishing_ == false) return;publisher_handle_count_--;NTSmartPublisherSDK.NT_PB_StopPublisher(publisher_handle_);if (0 == publisher_handle_count_){NTSmartPublisherSDK.NT_PB_Close(publisher_handle_);publisher_handle_ = IntPtr.Zero;}is_publishing_ = false;}

RTMP传输这块，需要把Event状态回调给Unity，确保Unity实时处理网络异常：

Unity层处理：

public event Action<uint,string> OnLogEventMsg;publisher_wrapper_.OnLogEventMsg += OnLogHandle;private void OnLogHandle(uint arg1, string arg2)
{Debug.Log(arg2);
}

wrapper层处理：

private void PbEventCallBack(IntPtr handle, IntPtr user_data, UInt32 event_id,Int64 param1,Int64 param2,UInt64 param3,UInt64 param4,[MarshalAs(UnmanagedType.LPStr)] String param5,[MarshalAs(UnmanagedType.LPStr)] String param6,IntPtr param7){String event_log = "";switch (event_id){case (uint)NTSmartPublisherDefine.NT_PB_E_EVENT_ID.NT_PB_E_EVENT_ID_CONNECTING:event_log = "连接中";if (!String.IsNullOrEmpty(param5)){event_log = event_log + " url:" + param5;}break;case (uint)NTSmartPublisherDefine.NT_PB_E_EVENT_ID.NT_PB_E_EVENT_ID_CONNECTION_FAILED:event_log = "连接失败";if (!String.IsNullOrEmpty(param5)){event_log = event_log + " url:" + param5;}break;case (uint)NTSmartPublisherDefine.NT_PB_E_EVENT_ID.NT_PB_E_EVENT_ID_CONNECTED:event_log = "已连接";if (!String.IsNullOrEmpty(param5)){event_log = event_log + " url:" + param5;}break;case (uint)NTSmartPublisherDefine.NT_PB_E_EVENT_ID.NT_PB_E_EVENT_ID_DISCONNECTED:event_log = "断开连接";if (!String.IsNullOrEmpty(param5)){event_log = event_log + " url:" + param5;}break;default:break;}if(OnLogEventMsg != null) OnLogEventMsg.Invoke(event_id, event_log);}

总结

以上是大概的流程，通过采集Unity的音视频数据，编码打包传输，发送到RTMP服务端，客户端直接拉取RTMP流数据，延迟在毫秒级，用户体验良好，在智慧数字人等交互场景，体验极佳。