very lag when dumping JTV HQ live stream

[pc323]

I use rtmpdump to dump the JTV HQ live stream and play it using VLC player with the following command
rtmpdump -r "rtmpurl" --jtv "jtvToken" --swfUrl "swfURL" -o - | "vlcPath" -
It can play the stream actually, but the video is very lag and the VLC is keeping buffering.
I found that rtmpdump doesn't download (XXXkB/ XXsec does not refresh) when the video is lag. Moreover, it shows some debug messages continuously during dumping.

DEBUG: HandleCtrl, received ctrl, type: 31, len: 6
DEBUG: HandleCtrl, Stream BufferEmpty 1

After a few minutes, the connection is closed because of the error.

DEBUG: RTMPSockBuf_Fill, recv returned -1. GetSockError(): 10053 (Unknown error)

ERROR: WriteN, RTMP send error 10053 (42 bytes)
ERROR: RTMP_ReadPacket, failed to read RTMP packet body. len: 12204
46889.657 kB / 322.61 sec
DEBUG: RTMP_Read returned: 0
Download complete
DEBUG: Closing connection.

What should I do? I don't want to use the flash player to play

Sorry for my Bad English skills...