[AR]n900 - Low latency webcam stream? - maemo.org

AndiThebest | # 1 | 2011-01-19, 22:49 | Report

Hi.

I want make a argumented reality car, controled by n900 accelerometer.
So i have a embedded debian board with makes a wlan-accesspoint, controls the car and sends a webcam stream to n900.

I have testet videostream from my laptop webcam to n900 (server and client = vlc) with 3 different ways:

Code:

server rtp:
vlc -vvv v4l2:///dev/video0 --sout '#transcode{vcodec=mp2v,acodec=mpga}:rtp{dst=CLIENTADRESSE,port=5000,sdp=file:///home/andi/sdp.sdp,ttl=10,mux=ts,proto=udp}'

client rtp:
open sdp.sdp file, generated by server
vlc file:///sdp.sdp

Code:

server udp multicast:
vlc -vvv v4l2:///dev/video0 --sout '#transcode{vcodec=mp2v,vb=800,scale=1,acodec=mpga,ab=128,channels=2,samplerate=44100}:std{access=udp,mux=ts,dst=239.255.23.23:1234}'

client:
vlc udp://@239.255.23.23:1234 :udp-caching=0

Code:

server mms stream:
vlc -vvv v4l2:///dev/video0 --sout '#transcode{vcodec=mp2v,vb=64,scale=1,acodec=mpga,ab=8,channels=1}:std{access=mmsh,mux=asfh,dst=:8080}'

client (n900, kmplayer, gstreamer/mplayer):
mms://SERVER:8080
via vlc:
vlc mmsh://SERVER:8080

My problem is, delay between webcam and n900(kmplayer/vlc) is ~2 seconds, thats too long.
Any ideas to decrase this latency?

Regards, Andi

aligatro | # 2 | 2011-01-19, 22:57 | Report

try to send uncompressed video, that should help, but wifi might be too slow for it.

epitaph | # 3 | 2011-01-19, 23:03 | Report

Originally Posted by AndiThebest View Post

Hi.

I want make a argumented reality car, controled by n900 accelerometer.
So i have a embedded debian board with makes a wlan-accesspoint, controls the car and sends a webcam stream to n900.

I have testet videostream from my laptop webcam to n900 (server and client = vlc) with 3 different ways:

Code:

server rtp:
vlc -vvv v4l2:///dev/video0 --sout '#transcode{vcodec=mp2v,acodec=mpga}:rtp{dst=CLIENTADRESSE,port=5000,sdp=file:///home/andi/sdp.sdp,ttl=10,mux=ts,proto=udp}'

client rtp:
open sdp.sdp file, generated by server
vlc file:///sdp.sdp

Code:

server udp multicast:
vlc -vvv v4l2:///dev/video0 --sout '#transcode{vcodec=mp2v,vb=800,scale=1,acodec=mpga,ab=128,channels=2,samplerate=44100}:std{access=udp,mux=ts,dst=239.255.23.23:1234}'

client:
vlc udp://@239.255.23.23:1234 :udp-caching=0

Code:

server mms stream:
vlc -vvv v4l2:///dev/video0 --sout '#transcode{vcodec=mp2v,vb=64,scale=1,acodec=mpga,ab=8,channels=1}:std{access=mmsh,mux=asfh,dst=:8080}'

client (n900, kmplayer, gstreamer/mplayer):
mms://SERVER:8080
via vlc:
vlc mmsh://SERVER:8080

My problem is, delay between webcam and n900(kmplayer/vlc) is ~2 seconds, thats too long.
Any ideas to decrase this latency?

Regards, Andi

u can use my tune-up utilities! it optimize network stack and install iptables and iproute. Other than that reduce color of webcam or compute all data onboard ( do u need a life image anyway ? ).

BTW: do u have fleury or hierholzer algo in php? i really need it!

Last edited by epitaph; 2011-01-19 at 23:23.

AndiThebest | # 4 | 2011-01-19, 23:35 | Report

thanks for fast replys!

Originally Posted by aligatro View Post

try to send uncompressed video, that should help, but wifi might be too slow for it.

Its not possible to stream without transcoding... when i use vlc without the transcode parameter:

Code:

vlc -vvv v4l2:///dev/video0 --sout '#std{access=udp,mux=ts,dst=239.255.23.23:1234}'

I'll get this output:

Code:

[0x29e1f68] main mux debug: adding a new input
[0x29e1f68] mux_ts mux debug: adding input codec=YUY2 pid=68
[0x29e1f68] main mux error: cannot add this stream
[0x29eb958] main packetizer error: cannot create packetizer output (YUY2)

Originally Posted by

u can use my tune-up utilities! it optimize network stack and install iptables and iproute. Other than that reduce color of webcam or compute all data onboard ( do u need a life image anyway ? ).

BTW: do u have fleury or hierholzer algo in php? i really need it!

Do you know how can i reduce quality and colors of the webcam? yes i want to have a life image.
btw: i am a php newbie

epitaph | # 5 | 2011-01-19, 23:45 | Report

i don't know. it should be some sort of freq filter on the server site. can't u just pipe video device through mplayer on server first i.e. preproccesing and then stream it with vlc? i don't have a fast algo here. also if u use my script u can get very low latency ping and upload dunno how much u can increase throughput but if u are really into it u should try it?

Last edited by epitaph; 2011-01-19 at 23:48.

aligatro | # 6 | 2011-01-19, 23:45 | Report

I didn't test this, but it might work.

Modified your server settings to

vlc -vvv v4l2:///dev/video0 --sout '#transcode{vcodec=mp1v,acodec=mpga,fps=10,vb=200} :rtp{dst=CLIENTADRESSE,port=5000,sdp=file:///home/andi/sdp.sdp,ttl=10,mux=ts,proto=udp}'

Frames per second is 10, bitrate is 200 kb/s and changed codec to Mpeg1.