问如何导入直播流并截取一帧

EN

private Capture capture = null;

private void btnStart_Click(object sender, System.EventArgs e)
        {
            try
            {
                if ( capture == null )
                    throw new ApplicationException( "Please select a video and/or audio device." );
                if ( !capture.Cued )
                    capture.Filename = txtFilename.Text;
                capture.Start();
                btnCue.Enabled = false;
                btnStart.Enabled = false;
            }
            catch (Exception ex)
            {
                MessageBox.Show( ex.Message + "\n\n" + ex.ToString() );
            }
        }