Unity下如何实现低延迟的全景RTMP|RTSP流渲染

技术背景

Unity3D可以用于创建各种类型的的应用程序，包括虚拟现实、培训模拟器等。以下是一些可以使用Unity3D全景播放的场景：

1. 虚拟现实体验：全景视频可以用来创建逼真的虚拟环境，使用户能够感受到身临其境的感觉；
2. 培训模拟器：全景视频可以用来创建真实的训练环境，例如飞行模拟器、驾驶模拟器等，以提供更加真实的训练体验；
3. 建筑设计：全景视频可以用来展示建筑设计的或室内装潢，使客户能够感受到真实的的效果；
4. 文旅导览：全景视频可以用来展示旅游景点或城市，使游客能够感受到身临其境的感觉。

在Unity3D平台上实现全景实时RTMP或RTSP流渲染，可以通过以下方式：

1. 获取全景视频数据源：首先，需要拉取RTMP或RTSP流数据，解码后，把RGB或YUV数据，回调到unity，从而获取到全景视频流数据；
2. Unity创建个Sphere，创建个材质球(Material)，并把材质球挂在到Sphere；
3. 实现实时渲染：使用Unity3D的渲染管道，您可以将纹理映射到球体或立方体的表面上，并使用着色器来处理纹理的坐标，以实现全景视频的实时渲染。

技术实现

本文以大牛直播SDK的RTMP推送端作为数据采集，获取全景窗体数据后，编码打包推送到RTMP服务，或启动个轻量级RTSP服务，对外提供个RTSP的拉流URL。

然后，播放端，拉取RTSP或RTMP的URL，把YUV或RGB数据回调上来，然后，再在Unity窗体绘制出来。

获取数据源：

    public void Play(int sel){if (videoctrl[sel].is_running){Debug.Log("已经在播放..");return;}lock (videoctrl[sel].frame_lock_){videoctrl[sel].cur_video_frame_ = null;}OpenPlayer(sel);if (videoctrl[sel].player_handle_ == IntPtr.Zero)return;//设置播放URLNTSmartPlayerSDK.NT_SP_SetURL(videoctrl[sel].player_handle_, videoctrl[sel].videoUrl);/* ++ 播放前参数配置可加在此处 ++ */int play_buffer_time_ = 0;NTSmartPlayerSDK.NT_SP_SetBuffer(videoctrl[sel].player_handle_, play_buffer_time_);                 //设置buffer timeint is_using_tcp = 0;        //TCP模式NTSmartPlayerSDK.NT_SP_SetRTSPTcpMode(videoctrl[sel].player_handle_, is_using_tcp);int timeout = 10;NTSmartPlayerSDK.NT_SP_SetRtspTimeout(videoctrl[sel].player_handle_, timeout);int is_auto_switch_tcp_udp = 1;NTSmartPlayerSDK.NT_SP_SetRtspAutoSwitchTcpUdp(videoctrl[sel].player_handle_, is_auto_switch_tcp_udp);Boolean is_mute_ = false;NTSmartPlayerSDK.NT_SP_SetMute(videoctrl[sel].player_handle_, is_mute_ ? 1 : 0);                    //是否启动播放的时候静音int is_fast_startup = 1;NTSmartPlayerSDK.NT_SP_SetFastStartup(videoctrl[sel].player_handle_, is_fast_startup);              //设置快速启动模式Boolean is_low_latency_ = false;NTSmartPlayerSDK.NT_SP_SetLowLatencyMode(videoctrl[sel].player_handle_, is_low_latency_ ? 1 : 0);    //设置是否启用低延迟模式//设置旋转角度(设置0， 90， 180， 270度有效，其他值无效)int rotate_degrees = 0;NTSmartPlayerSDK.NT_SP_SetRotation(videoctrl[sel].player_handle_, rotate_degrees);int volume = 100;NTSmartPlayerSDK.NT_SP_SetAudioVolume(videoctrl[sel].player_handle_, volume);	//设置播放音量, 范围是[0, 100], 0是静音，100是最大音量, 默认是100// 设置上传下载报速度int is_report = 0;int report_interval = 2;NTSmartPlayerSDK.NT_SP_SetReportDownloadSpeed(videoctrl[sel].player_handle_, is_report, report_interval);/* -- 播放前参数配置可加在此处 -- *///video frame callback (YUV/RGB)videoctrl[sel].video_frame_call_back_ = new SP_SDKVideoFrameCallBack(NT_SP_SetVideoFrameCallBack);NTSmartPlayerSDK.NT_SP_SetVideoFrameCallBack(videoctrl[sel].player_handle_, (Int32)NT.NTSmartPlayerDefine.NT_SP_E_VIDEO_FRAME_FORMAT.NT_SP_E_VIDEO_FRAME_FROMAT_I420, window_handle_, videoctrl[sel].video_frame_call_back_);UInt32 flag = NTSmartPlayerSDK.NT_SP_StartPlay(videoctrl[sel].player_handle_);if (flag == DANIULIVE_RETURN_OK){videoctrl[sel].is_need_get_frame_ = true;Debug.Log("播放成功");}else{videoctrl[sel].is_need_get_frame_ = false;Debug.LogError("播放失败");}videoctrl[sel].is_running = true;}

针对数据处理：

    private void SDKVideoFrameCallBack(UInt32 status, IntPtr frame, int sel){//这里拿到回调frame，进行相关操作NT_SP_VideoFrame video_frame = (NT_SP_VideoFrame)Marshal.PtrToStructure(frame, typeof(NT_SP_VideoFrame));VideoFrame  u3d_frame = new VideoFrame();u3d_frame.width_  = video_frame.width_;u3d_frame.height_ = video_frame.height_;u3d_frame.timestamp_ = (UInt64)video_frame.timestamp_;int d_y_stride = video_frame.width_;int d_u_stride = (video_frame.width_ + 1) / 2;int d_v_stride = d_u_stride;int d_y_size = d_y_stride * video_frame.height_;int d_u_size = d_u_stride * ((video_frame.height_ + 1) / 2);int d_v_size = d_u_size;int u_v_height = ((u3d_frame.height_ + 1) / 2);u3d_frame.y_stride_ = d_y_stride;u3d_frame.u_stride_ = d_u_stride;u3d_frame.v_stride_ = d_v_stride;u3d_frame.y_data_ = new byte[d_y_size];u3d_frame.u_data_ = new byte[d_u_size];u3d_frame.v_data_ = new byte[d_v_size];CopyFramePlane(u3d_frame.y_data_, d_y_stride,video_frame.plane0_, video_frame.stride0_, u3d_frame.height_);CopyFramePlane(u3d_frame.u_data_, d_u_stride,video_frame.plane1_, video_frame.stride1_, u_v_height);CopyFramePlane(u3d_frame.v_data_, d_v_stride,video_frame.plane2_, video_frame.stride2_, u_v_height);lock (videoctrl[sel].frame_lock_ ){videoctrl[sel].cur_video_frame_ = u3d_frame;}}

刷新Texture：

private void UpdateYUVTexture(VideoFrame video_frame, int sel)
{if (video_frame.y_data_ == null || video_frame.u_data_ == null || video_frame.v_data_ == null){Debug.Log("video frame with null..");return;}if (videoctrl[sel].yTexture_ != null){videoctrl[sel].yTexture_.LoadRawTextureData(video_frame.y_data_);videoctrl[sel].yTexture_.Apply();}if (videoctrl[sel].uTexture_ != null){videoctrl[sel].uTexture_.LoadRawTextureData(video_frame.u_data_);videoctrl[sel].uTexture_.Apply();}if (videoctrl[sel].vTexture_ != null){videoctrl[sel].vTexture_.LoadRawTextureData(video_frame.v_data_);videoctrl[sel].vTexture_.Apply();}
}

全景播放的时候，如果需要移动显示区域，可以用以下代码：

public class MouseMove : MonoBehaviour {Vector2 p1, p2;private Vector3 PreMouseMPos;private Vector3 PreMouseLPos;public float minimumY = -60F;public float maximumY = 60F;float rotationY = 0F;private float wheelSpeed = 5.0f;// Use this for initializationvoid Start () {}// Update is called once per framevoid Update () {if (Input.GetMouseButton(0)){if (PreMouseLPos.x <= 0){PreMouseLPos = new Vector3(Input.mousePosition.x, Input.mousePosition.y, 0.0f);}else{Vector3 CurMouseLPos = new Vector3(Input.mousePosition.x, Input.mousePosition.y, 0.0f);Vector3 offset = CurMouseLPos - PreMouseLPos;Quaternion tt = Quaternion.Euler(offset);float rotationX = transform.localEulerAngles.y - tt.x * 20;rotationY += tt.y * 20;rotationY = Mathf.Clamp(rotationY, minimumY, maximumY);transform.localEulerAngles = new Vector3(rotationY, rotationX, 0);PreMouseLPos = CurMouseLPos;}}else{PreMouseLPos = new Vector3(0.0f, 0.0f, 0.0f);}}
}

总结

Unity全景播放RTMP或RTSP实时流，可以广泛用于各种需要提供真实场景或沉浸式体验的场景，为用户带来更加逼真的体验。与此同时，Unity全景实时播放，需要有非常高的延迟要求和性能要求，特别是全景数据源，分辨率和码率都非常高，对解码效率和解码后的数据拷贝投递，提了更高的要求。