Logitech C920, streaming H.264

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v4l2-ctl --device=/dev/video1 --set-fmt-video=width=800,height=600,pixelformat=1

cvlc v4l2:///dev/video1 --demux h264

cvlc v4l2:///dev/video1:chroma=h264

playback works. we get a H264 stream from the cam. now let's stream it over the network via HTTP:

cvlc v4l2:///dev/video1:chroma=h264:width=800:height=600 --sout '#standard{access=http,mux=ts,dst=localhost:8080,name=stream,mime=video/ts}' -vvv

mplayer http://localhost:8080/

turns out, MPEG-TS enables mplayer to hook into the stream at any time with a slight delay (probably waiting for a keyframe or sth like that)
if you use mux=avi,mime=video/avi instead, you need to start mplayer in the very moment you start vlc, else mplayer will not start playing

if you try ffmpeg instead of vlc for playback, you will probably encounter this problem: https://ffmpeg.org/trac/ffmpeg/ticket/1387
as soon as you start ffmpeg, it will switch back to "Video: rawvideo (YUY2 / 0x32595559)"
while it accepts MJPEG, it won't work with H.264
same apparently happens when using qv4l2: Start capturing in H264 mode actually gives you a YUY2 video window

mplayer is capable of playback on the framebuffer, make sure X is not running and type:

mplayer http://192.168.1.100:8080/ -fs -framedrop -vo fbdev

Xorg -retro &> /dev/zero

there are loads of fbdev error messages coming up, which we silently discard into /dev/zero
play video stream from LAN vlc source (see section above):

DISPLAY=":0" mplayer http://192.168.1.100:8080/ -fs -framedrop

if we do so, we will notice that we do not make use of Xvideo or any kind of hardware acceleration yet
http://linux-sunxi.org/CedarX seems to provide us with a VPU library, which unfortunately is Allwinner's proprietary non-free thing
but a hacked VLC exists, which can make use of it: http://linux-sunxi.org/VLC
compiled successfully: https://github.com/matthiasbock/VideoLAN-for-Allwinner-A10-VPU

In case you experience ugly, choppy artifacts in the picture, while streaming from a Raspberry Pi using

cvlc v4l2:///dev/video0:chroma=h264 ...

you might need to upgrade your firmware:

apt-get install rpi-update raspi-config
rpi-update
reboot

Solved the problem for me.