ffserver.conf:
    <Feed stream.ffm>
        File /tmp/stream.ffm
        FileMaxSize 20000K
    </Feed>
    <Stream thumb.jpg>
        Feed stream.ffm
        Format mpjpeg
        NoAudio
        Strict -1
    </Stream>


command line:
    ffmpeg -i socket.mpg http://localhost:8090/stream.ffm

where socket.mpg is a symlink to /dev/video0, which is an mpeg stream


errors:

[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow6kB time=2.0 bitrate= 229.4kbits/s
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow2kB time=4.8 bitrate= 225.3kbits/s
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
[mjpeg @ 0x84118dc]rc buffer underflow
.....