RTSP Streaming. How to create Gst.Buffer

General Discussion
1

Hi,

I’m using Gstreamer to write EmguCv UMat frames to rtspclientsink to create RTSP streaming with Mediamtx server.

I want to know what is the best way to write frames to Gst.Buffer. I want to have the best performance and avoid as possible temporal memory copies. Here are my results using two different ways to create the Gst.Buffer.

This is my pipeline.


var command = new StringBuilder();
command.Append("appsrc name=appSource is-live=true do-timestamp=true");
command.Append(" ! videoconvert");
command.Append(" ! qsvh264enc bitrate=10000 low-latency=true target-usage=7");
command.Append(" ! h264parse ");
command.AppendFormat(" ! rtspclientsink location={0}", _streamUrl);
 
_pipeline = Parse.Launch(command.ToString()) as Pipeline;
_pipeline.Bus.AddWatch(OnBusMessage);

var appSrcElement = _pipeline.GetByName("appSource");
_appSrc = new AppSrc(appSrcElement.Handle);
_appSrc.StreamType = AppStreamType.Stream;
_appSrc.Block = true;
_appSrc.Format = Format.Time;
 
var caps = Caps.FromString("video/x-raw, format=BGR, width=640, height=480, framerate=30/1");
_appSrc.Caps = caps;

Creating the Gst.Buffer using byte[] seems to be working well.

public FlowReturn WriteFrame(UMat img)
{
    FlowReturn res;
    CvInvoke.Resize(img, img, new System.Drawing.Size(640, 480));
    using (var mat = img.GetMat(Emgu.CV.CvEnum.AccessType.Read))
    {
        var length = mat.Rows * mat.Cols * mat.NumberOfChannels;
        var data = new byte[length];
        Marshal.Copy(mat.DataPointer, data, 0, length);
        var buffer = new Gst.Buffer(data);
        res = _appSrc.PushBuffer(buffer);
    }
}

But before I have try to use Map, with that the stream works and there is no error but the streaming shows black image.

var buffer = new Gst.Buffer(null, (ulong)length, AllocationParams.Zero);
if (buffer.Map(out var mapInfo, MapFlags.Write))
{
    try
    {
        Marshal.Copy(mat.DataPointer, mapInfo.Data, 0, length);
    }
    finally
    {
        buffer.Unmap(mapInfo);
    }
}

With regards,