使用C＃/ASP.NET MVC进行逐帧MJPEG流传输

Question

我一直在尝试在ASP.NET中设置一个MJPEG流。我想从URL检索MJPEG流，并将收到的每一帧发送给每个连接的客户端。我找到的示例只能从一个预设文件中读取，而不是从URL中连续流式传输，并通过 MultiStreamContent 发送整个文件。由于我逐帧检索，所以我不能这样做。 我想知道是否可以使用ASP.NET MVC实现我的需求。我目前正在使用AForge视频从链接中检索MJPE流。 我的控制器类代码：

using System.Net.Http;
using System.Web.Http;
using AForge.Video;

namespace VideoPrototypeMVC.Controllers
{
    public class CameraController : ApiController
    {
        int framecounter = 0;
        MJPEGStream stream = new MJPEGStream();

        [HttpGet]
        public void GetVideoContent()
        {   
            stream.Source = @"http://127.0.0.1:5002/stream";
            stream.NewFrame += new NewFrameEventHandler(showFrame);
            stream.Start();
            MultipartContent content = new MultipartContent();
            while (stream.IsRunning)
            {
            //Continues streaming should be here?
            }
        }

        //Can be used to display of a frame is available
        private void showFrame(object sender, NewFrameEventArgs eventArgs)
        {
            framecounter++;
            System.Diagnostics.Debug.WriteLine("New frame event: " + framecounter);

        }

        //Should be called at the end of the stream
        private void stopStream(object sender, ReasonToFinishPlaying reason)
        {
            System.Diagnostics.Debug.WriteLine("Stop stream");
            stream.Stop();
            framecounter = 0;
        }
    }
}

这段代码不是最终版本，但我只需要让连续流正常运行。我找到了一些使用Socket服务器的示例，但我想坚持使用MVC，因为它可以更轻松地设置服务器的其余部分。

- Arastelion

---

如果我正确理解了你的问题，你拥有一个设备向你发送MJPEG流，并且你想要将相同的MJPEG流提供给连接到你的ASP.NET MVC应用程序的多个用户？如果你通过依赖注入、静态变量等方式共享你的MJPEG客户端，那么你可以做到这一点。每个请求只需等待新帧的到来，并在到达时将其发送到客户端。你可以使用MultiStreamContent将数据发送给你的客户端；当你等待更多的帧到达时，连接将保持打开（并处于空闲状态）。 - Frederik Carlier

检查 PushStreamContent。当第一个请求到达时 - 启动您的MJPEG流并将帧写入所有连接的响应流。当最后一个客户端断开连接时 - 停止您的MJPEG流。 - Evk

PushStreamContent，我只在直接文件流的上下文中找到了它，如果我传递一个流URL，它也能工作吗？@Evk - Arastelion

你从MJPEGStream接收到的帧是一个字节数组（我这里假设是这样）。然后，你可以直接将这个字节数组写入到连接客户端的响应中。PushStreamContent允许你以异步方式将内容写入响应流（也就是说，在你的MVC方法已经“返回”之后再进行写入）。你可以向响应流中写入任何内容，不仅限于文件。 - Evk

@Evk，您的建议听起来像是一个答案... - Fildor

Answer 1

为了确保其他人也能够管理这个问题，我将@Evk（再次感谢您）所说的内容和我在这里找到的信息结合起来：创建自己的MJPEG流。请注意：下面的代码只是原型/概念验证！当我运行这段代码时，我的处理器飙升到100％，因为StartStream中存在无尽的while循环。会继续工作，使其更加基于事件，但我认为下面的代码更容易解释。

using System;
using System.IO;
using System.Net;
using System.Web;
using System.Net.Http;
using System.Web.Http;
using AForge.Video;
using System.Drawing;
using System.Text;
using System.Drawing.Imaging;
using System.Threading;

namespace VideoPrototypeMVC.Controllers
{
    public class CameraController : ApiController
    {
        private MJPEGStream mjpegStream = new MJPEGStream();
        private bool frameAvailable = false;
        private Bitmap frame = null;
        private string BOUNDARY = "frame";

        /// <summary>
        /// Initializer for the MJPEGstream
        /// </summary>
        CameraController()
        {
            mjpegStream.Source = @"{{INSERT STREAM URL}}";
            mjpegStream.NewFrame += new NewFrameEventHandler(showFrameEvent);
        }

        [HttpGet]
        public HttpResponseMessage GetVideoContent()
        {   
            mjpegStream.Start();
            var response = Request.CreateResponse();
            response.Content = new PushStreamContent((Action<Stream, HttpContent, TransportContext>)StartStream);
            response.Content.Headers.ContentType = System.Net.Http.Headers.MediaTypeHeaderValue.Parse("multipart/x-mixed-replace; boundary=" + BOUNDARY);
            return response;
        }

        /// <summary>
        /// Craete an appropriate header.
        /// </summary>
        /// <param name="length"></param>
        /// <returns></returns>
        private byte[] CreateHeader(int length)
        {
            string header =
                "--" + BOUNDARY + "\r\n" +
                "Content-Type:image/jpeg\r\n" +
                "Content-Length:" + length + "\r\n\r\n";

            return Encoding.ASCII.GetBytes(header);
        }

        public byte[] CreateFooter()
        {
            return Encoding.ASCII.GetBytes("\r\n");
        }

        /// <summary>
        /// Write the given frame to the stream
        /// </summary>
        /// <param name="stream">Stream</param>
        /// <param name="frame">Bitmap format frame</param>
        private void WriteFrame(Stream stream, Bitmap frame)
        {
            // prepare image data
            byte[] imageData = null;

            // this is to make sure memory stream is disposed after using
            using (MemoryStream ms = new MemoryStream())
            {
                frame.Save(ms, ImageFormat.Jpeg);
                imageData = ms.ToArray();
            }

            // prepare header
            byte[] header = CreateHeader(imageData.Length);
            // prepare footer
            byte[] footer = CreateFooter();

            // Start writing data
            stream.Write(header, 0, header.Length);
            stream.Write(imageData, 0, imageData.Length);
            stream.Write(footer, 0, footer.Length);
        }

        /// <summary>
        /// While the MJPEGStream is running and clients are connected,
        /// continue sending frames.
        /// </summary>
        /// <param name="stream">Stream to write to.</param>
        /// <param name="httpContent">The content information</param>
        /// <param name="transportContext"></param>
        private void StartStream(Stream stream, HttpContent httpContent, TransportContext transportContext)
        {
            while (mjpegStream.IsRunning && HttpContext.Current.Response.IsClientConnected)
            {
                if (frameAvailable)
                {
                    try
                    {
                        WriteFrame(stream, frame);
                        frameAvailable = false;
                    } catch (Exception e)
                    {
                        System.Diagnostics.Debug.WriteLine(e);
                    }
                }else
                {
                    Thread.Sleep(30);
                }
            }
            stopStream();
        }

        /// <summary>
        /// This event is thrown when a new frame is detected by the MJPEGStream
        /// </summary>
        /// <param name="sender">Object that is sending the event</param>
        /// <param name="eventArgs">Data from the event, including the frame</param>
        private void showFrameEvent(object sender, NewFrameEventArgs eventArgs)
        {
            frame = new Bitmap(eventArgs.Frame);
            frameAvailable = true;
        }

        /// <summary>
        /// Stop the stream.
        /// </summary>
        private void stopStream()
        {
            System.Diagnostics.Debug.WriteLine("Stop stream");
            mjpegStream.Stop();
        }
    }
}

- Arastelion

---

如果你想改进这段程序并去掉无尽循环: 使用showFrameEvent。每当接收到帧时，其中的任何代码都会被执行。 - Arastelion

因此，上面的代码似乎非常好用 - 如果是这样，谢谢。 - Richard Housham

Answer 2

Arastelion 的回答很好，但我注意到如果您离开应用程序，则仍然会在后台进行请求，这可能会消耗资源。 在 stopStream 之后添加 stream.FlushAsync();、stream.Close(); 和 stream.Dispose(); 似乎可以解决这个问题。

using System;
using System.IO;
using System.Net;
using System.Web;
using System.Net.Http;
using System.Web.Http;
using AForge.Video;
using System.Drawing;
using System.Text;
using System.Drawing.Imaging;
using System.Threading;

namespace VideoPrototypeMVC.Controllers
{
    public class CameraController : ApiController
    {
        private MJPEGStream mjpegStream = new MJPEGStream();
        private bool frameAvailable = false;
        private Bitmap frame = null;
        private string BOUNDARY = "frame";

        /// <summary>
        /// Initializer for the MJPEGstream
        /// </summary>
        CameraController()
        {
            mjpegStream.Source = @"{{INSERT STREAM URL}}";
            mjpegStream.NewFrame += new NewFrameEventHandler(showFrameEvent);
        }

        [HttpGet]
        public HttpResponseMessage GetVideoContent()
        {   
            mjpegStream.Start();
            var response = Request.CreateResponse();
            response.Content = new PushStreamContent((Action<Stream, HttpContent, TransportContext>)StartStream);
            response.Content.Headers.ContentType = System.Net.Http.Headers.MediaTypeHeaderValue.Parse("multipart/x-mixed-replace; boundary=" + BOUNDARY);
            return response;
        }

        /// <summary>
        /// Craete an appropriate header.
        /// </summary>
        /// <param name="length"></param>
        /// <returns></returns>
        private byte[] CreateHeader(int length)
        {
            string header =
                "--" + BOUNDARY + "\r\n" +
                "Content-Type:image/jpeg\r\n" +
                "Content-Length:" + length + "\r\n\r\n";

            return Encoding.ASCII.GetBytes(header);
        }

        public byte[] CreateFooter()
        {
            return Encoding.ASCII.GetBytes("\r\n");
        }

        /// <summary>
        /// Write the given frame to the stream
        /// </summary>
        /// <param name="stream">Stream</param>
        /// <param name="frame">Bitmap format frame</param>
        private void WriteFrame(Stream stream, Bitmap frame)
        {
            // prepare image data
            byte[] imageData = null;

            // this is to make sure memory stream is disposed after using
            using (MemoryStream ms = new MemoryStream())
            {
                frame.Save(ms, ImageFormat.Jpeg);
                imageData = ms.ToArray();
            }

            // prepare header
            byte[] header = CreateHeader(imageData.Length);
            // prepare footer
            byte[] footer = CreateFooter();

            // Start writing data
            stream.Write(header, 0, header.Length);
            stream.Write(imageData, 0, imageData.Length);
            stream.Write(footer, 0, footer.Length);
        }

        /// <summary>
        /// While the MJPEGStream is running and clients are connected,
        /// continue sending frames.
        /// </summary>
        /// <param name="stream">Stream to write to.</param>
        /// <param name="httpContent">The content information</param>
        /// <param name="transportContext"></param>
        private void StartStream(Stream stream, HttpContent httpContent, TransportContext transportContext)
        {
            while (mjpegStream.IsRunning && HttpContext.Current.Response.IsClientConnected)
            {
                if (frameAvailable)
                {
                    try
                    {
                        WriteFrame(stream, frame);
                        frameAvailable = false;
                    } catch (Exception e)
                    {
                        System.Diagnostics.Debug.WriteLine(e);
                    }
                }else
                {
                    Thread.Sleep(30);
                }
            }
            stopStream();
            stream.FlushAsync();
            stream.Close();
            stream.Dispose();
        }

        /// <summary>
        /// This event is thrown when a new frame is detected by the MJPEGStream
        /// </summary>
        /// <param name="sender">Object that is sending the event</param>
        /// <param name="eventArgs">Data from the event, including the frame</param>
        private void showFrameEvent(object sender, NewFrameEventArgs eventArgs)
        {
            frame = new Bitmap(eventArgs.Frame);
            frameAvailable = true;
        }

        /// <summary>
        /// Stop the stream.
        /// </summary>
        private void stopStream()
        {
            System.Diagnostics.Debug.WriteLine("Stop stream");
            mjpegStream.Stop();
        }

         protected override void Dispose(bool disposing)
         {
            if (disposing)
             {
                 stopStream();
             }

             base.Dispose(disposing);
           } 


    }
}

- Richard Housham