I want to transcode MJPEG stream that comes from IP camera (http://xx.yy.zz.tt:8080/video.cgi) to FLV or MP4 stream under Linux OS so that users can play the file using a we
appears VLC can do HTTP authentication. http://www.videolan.org/doc/play-howto/en/ch04.html and I believe it can output to flv. Typically I start things going by using the GUI to see what it is using as parameters, then go from there. There's no magic formula there, mate.
Appears you can output to flv by something similar to:
:sout=#transcode{vcodec=h264,vb=0,scale=0,acodec=mp3,ab=128,channels=2,samplerate=44100}:http{mux=ffmpeg{mux=flv},dst=:8080/}
http://forum.videolan.org/viewtopic.php?f=14&t=80722
Also might work FFmpeg with url like http://user:password@host:port/address
ref: https://ffmpeg.zeranoe.com/forum/viewtopic.php?t=1139