如何使用 .NET Core 解析 MPEG 视频流 [英] How to Parse an MPEG Video Stream using .NET Core

问题描述

对于个人项目，我试图从 IP 摄像机的 MPEG 流中读取数据，并对接收到的各个帧执行一些计算机视觉任务(使用 .NET Core 2.2).

For a personal project, I am attempting to read from a IP Camera's MPEG stream and perform some computer-vision tasks on the individual frames I receive (Using .NET Core 2.2).

我向摄像机的 MPEG 端点执行 GET 请求，然后返回一个 multipart/x-mixed-replace 响应，该响应连续流式传输看似单个帧的内容作为 JPEG 图像.

I perform a GET request to the Camera's MPEG endpoint and I'm returned a multipart/x-mixed-replace response that continually streams what appear to be individual frames as JPEG images.

我无法理解的是从多部分响应中解析出帧的正确方法 - 如何检索帧对我来说并不重要，如果有更好的解析方法这种流，我当然愿意改变 - 视频检索/处理对我来说是一个全新的世界:)

What I'm having trouble understanding is the correct way to parse out the frames from the multi-part response - how the frames are retrieved is unimportant to me, if there's a better way to parse this kind of stream, I'm certainly open to change - video retrieval/processing is a whole new world for me :)

供参考:

MPEG 端点:

GET http://192.168.0.14/mjpeg.cgi

示例响应头:

Content-Type: multipart/x-mixed-replace;boundary=--video boundary--

示例响应正文:

Content-length: 41142
Date: 02-02-2019 12:43:19 AM
Content-type: image/jpeg

[payload]

--video boundary--
Content-length: 41220
Date: 02-02-2019 12:43:19 AM
Content-type: image/jpeg

[payload]

--video boundary--

我目前所拥有的:

var client = new HttpClient() {
    BaseAddress = new Uri(streamUrl)
};

var stream = await client.GetStreamAsync(resource);

using (var streamReader = new StreamReader(stream)) {                
    while(true) {
        await GetFrameStart(streamReader);
        var frame = await ReadFrame(streamReader);

        // Get byte[] from returned frame above and construct image
    };
}

// ---

// Fast forward to the start of the Frame's bytes
static async Task GetFrameStart(StreamReader reader) {
    string buffer = null;
    while (buffer != string.Empty) {
        buffer = await reader.ReadLineAsync();
    }
}

// Read entire byte array until the video boundary is met
static async Task<String> ReadFrame(StreamReader reader) {
    string result = string.Empty;
    string line = null;

    while(!isBoundary(line)) {
        line = await reader.ReadLineAsync();
        if (!isBoundary(line)) result += line;
    };

    return result;
}

上面似乎给了我每个帧的单独 [payload]，但是如果我将字符串转换为字节并写入磁盘时，图像不是有效的 jpeg:

The above seems to be giving me back the individual [payload] of each frame, however if I when I convert the string to bytes and write to disk, the image is not a valid jpeg:

var bytes = Encoding.UTF8.GetBytes(frame);

using (var fs = new FileStream("test.jpeg", FileMode.Create, FileAccess.Write)) {
    fs.Write(bytes, 0, bytes.Length);
}

推荐答案

您可以使用 Microsoft.AspNetCore.WebUtilities.MultipartReader

 var boundary = GetBoundary(context.Request.ContentType);
 var reader = new MultipartReader(boundary, context.Request.Body);
 var section = await reader.ReadNextSectionAsync();

有关详细信息，请参阅此答案:

See this Answer for more info:

希望这会有所帮助.

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