[drbmn]

This is because librtmp is sending pause/unpause when Stream BufferEmpty.
You can see this by turn on debug message "-V", and you will see,

DEBUG: HandleCtrl, received ctrl. type: 31, len: 6
DEBUG: HandleCtrl, Stream BufferEmpty 1
DEBUG: RTMP_SendPause, 1, pauseTime=0
DEBUG: Invoking pause

I try disable sending pause by comment out the following line in librtmp/rtmp.c,

if (!(r->Link.lFlags & RTMP_LF_BUFX))
break;

Only comment the first line, and let the break command uncommented,

// if (!(r->Link.lFlags & RTMP_LF_BUFX))
break;

It works!