对于个人项目,我试图从IP摄像机的MPEG流中读取数据,并在收到的各个帧上执行一些计算机视觉任务(使用.NET Core 2.2)。
我向摄像机的MPEG端点执行GET
请求,并且返回了multipart/x-mixed-replace
响应,该响应不断将看起来像是单个帧的内容作为JPEG图像流传输。
我无法理解的是从多部分响应中解析出帧的正确方法-如何对于我来说,获取帧并不重要,如果有更好的方法来解析这种流,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:)
供参考:
MPEG端点:
GET http://192.168.0.14/mjpeg.cgi
示例响应标题:
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--
到目前为止我所拥有的:
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;
}
上面的代码似乎让我还了每一帧的单独[有效负载],但是如果我将字符串转换为字节并写入磁盘时,该图像不是有效的jpeg:
var bytes = Encoding.UTF8.GetBytes(frame);
using (var fs = new FileStream("test.jpeg", FileMode.Create, FileAccess.Write)) {
fs.Write(bytes, 0, bytes.Length);
}
您可以在一行中使用ffmpeg:
ffmpeg -i http://192.168.0.14/mjpeg.cgi -vcodec copy frame%d.jpg
这将提取所有带有编号名称的帧。
如果安装ffmpeg,则可以使用System.Diagnostics.Process这样从应用程序中调用它:
var process = new Process()
{
StartInfo = new ProcessStartInfo()
{
FileName = "ffmpeg",
Arguments = "-i http://192.168.0.14/mjpeg.cgi -vcodec copy frame%d.jpg",
UseShellExecute = false,
CreateNoWindow = true,
RedirectStandardOutput = true,
RedirectStandardError = true
},
EnableRaisingEvents = true
};
process.ErrorDataReceived += (sender, data) => Console.WriteLine(data.Data);
process.Start();
process.BeginErrorReadLine();