Posts Tagged ‘prefix’

Capturing Video from WebCamera in Console and Terminal on Linux with good old ffmpeg

Tuesday, December 18th, 2012


Capturing video from webcamera in Skype and Desktop on Debian Ubuntu Fedora Linux Desktop - tux director webcamera recording from skype and desktop ffmpeg

Two articles, before I've blogged on how one can take pictures from console / terminal with ffmpeg. It was interesting fact, I've stumbled on ffmpeg is able of capturing video executed from terminal or plain console TTY.


The command to do so is:

# ffmpeg -f video4linux2 -r 25 -s 640x480 -i /dev/video0 webcam-movie.avi
FFmpeg version SVN-r25838, Copyright (c) 2000-2010 the FFmpeg developers
  built on Sep 20 2011 17:00:01 with gcc 4.4.5
  configuration: --enable-libdc1394 --prefix=/usr --extra-cflags='-Wall -g ' --cc='ccache cc' --enable-shared --enable-libmp3lame --enable-gpl --enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid --enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libspeex --enable-nonfree --disable-stripping --enable-avfilter --enable-libdirac --disable-decoder=libdirac --enable-libschroedinger --disable-encoder=libschroedinger --enable-version3 --enable-libopenjpeg --enable-libvpx --enable-librtmp --extra-libs=-lgcrypt --disable-altivec --disable-armv5te --disable-armv6 --disable-vis
  libavutil     50.33. 0 / 50.43. 0
  libavcore      0.14. 0 /  0.14. 0
  libavcodec    52.97. 2 / 52.97. 2
  libavformat   52.87. 1 / 52.87. 1
  libavdevice   52. 2. 2 / 52. 2. 2
  libavfilter    1.65. 0 /  1.65. 0
  libswscale     0.12. 0 /  0.14. 1
  libpostproc   51. 2. 0 / 51. 2. 0

Like you can see in accordance with WebCamera maximum supported resolution, one can change 640×480 to higher in case if attached expensive HD webcam.

Note that the webcamera should not be in use when issuing the command, otherwise because /dev is used you will get:

[video4linux2 @ 0x633160] Cannot find a proper format for codec_id 0, pix_fmt -1. /dev/video0: Input/output error

It is another interesting, topic I thought if if i t is possible to somehow caputre the Video streamed currently, whether for example in Skype there is a Skype conference established, but unfortunately it is not possible to do it with ffmpeg, cause /dev/video0 is in use while Skype Video stream flows.

There is another way to record Skype and other Programs recording from the WebCam (i.e. Cheese) by using  a small command line tool recordmydesktop.

To use recordmydesktop to save (record) Skype Video Conference just run it in advance and afterwardsmake your Skype call. To capture input from the WebCam while it is in use there are two other GUI instruments capturing the Active Desktop – e.g. Istanbul and vnc2swf.  If you never used any of those and you want to read short review on them check out my older article – Best Software Available Today for GNU / Linux Desktop capturing on Debian

The The little problem with recording the desktop is that if you want to record the Skype conference and straight use the software you will catch also the rest of the Desktop, however it is possible to set recordmydesktop to record content from a Windows with specific ID, so recording only skype Video  should be possible too.

I was intrigued by the question if after all Video Capturing is possible while Video is Streamed from WebCam with ffmpeg, so did a quick research for the command line freaks, here is how:

ffmpeg -f x11grab -s `xdpyinfo | grep -i dimensions: | sed 's/[^0-9]*pixels.*(.*).*//' | sed 's/[^0-9x]*//'` -r 25 -i :0.0 -sameq recorder-video-from-cam.avi

The only problem with this command line is the video captured from webcamera will be without sound. To take the Video and Sound input with ffmpeg use:

ffmpeg -f alsa -ac 2 -i pulse -f x11grab -r 30 -s 1024x768 -i :0.0 -acodec pcm_s16le -vcodec libx264 -vpre lossless_ultrafast -threads 0


On Debian and Ubuntu Linux, there is also GUI recordmydesktop the package name to install is gtk-recordmydesktop. GTK-RecordMyDesktop, works pretty well, so probably for people looking for convenience and ex-Windows GUI oriented Linux
users it is best choice

To use it on Debian:

# apt-get --yes install gtk-recordmydesktop

and launch it with cmd:

# gtk-recordmydesktop

recording  Skype and Desktop Webcam Video on Windows program allowing capture / record content from webcam from certain Window

As you can see in above, screenshot GTK-Screenshot can select a Certain Window on Desktop to record, so with it it is a piece of cake to:

1. start the Skype Video  conference
2. Launch gtk-recordmydesktop
3. Press Select Window and Select Skype Video Stream

I'm curious if the pointed Skype + gtk-recordmydesktop, method to capture Skype Active videos will be working on FreeBSD. Unfortunately I don't have FreeBSD Desktop with attached WebCam to give it a, try I will be very thankful, if someone using FreeBSD / NetBSD happen to read this article and take few minutes to test if it works and drop a comment below.

That's all, Enjoy, your captured video with sound 😉

How to solve “IPv6 addrconf: prefix with wrong length 48”

Friday, December 9th, 2011

While reading some log files on one of the co-located servers at , I’ve noticed dmesg log was filling in with tons of junk messages like:

[4288245.609762] IPv6 addrconf: prefix with wrong length 48
[4288445.984153] IPv6 addrconf: prefix with wrong length 48
[4288646.296110] IPv6 addrconf: prefix with wrong length 48
[4288846.609119] IPv6 addrconf: prefix with wrong length 48
[4289046.922604] IPv6 addrconf: prefix with wrong length 48
[4289247.267273] IPv6 addrconf: prefix with wrong length 48
[4289447.545800] IPv6 addrconf: prefix with wrong length 48
[4289647.857789] IPv6 addrconf: prefix with wrong length 48
[4289848.169308] IPv6 addrconf: prefix with wrong length 48
[4290048.595104] IPv6 addrconf: prefix with wrong length 48
[4290248.808497] IPv6 addrconf: prefix with wrong length 48
[4290449.103503] IPv6 addrconf: prefix with wrong length 48
[4290649.418747] IPv6 addrconf: prefix with wrong length 48
[4290849.742731] IPv6 addrconf: prefix with wrong length 48

After checking the message to make sure it would not suddeny lead to server hang ups I figured out the message is not dangerous but just an annoying warning that some other (routing) host on the same network as mine is advertising something using IPv6, that doesn’t fit with my IPv6 server config.
Actually the server doesn’t use the IPv6 configuration at all, and the assigned configuration is just some kind of auto set IPv6 IP address.
The server, where this message appeared is powered by 64 bit Debian GNU / Linux Squeeze

To resolve the annoying message, 5 of the kernel sysctl settings needs to be modified with cmds:

debian:~# sysctl net.ipv6.conf.all.accept_ra=0
debian:~# sysctl net.ipv6.conf.all.autoconf=0
debian:~# sysctl net.ipv6.conf.lo.autoconf=0
debian:~# sysctl net.ipv6.conf.eth0.autoconf=0
debian:~# sysctl net.ipv6.conf.eth1.autoconf=0

Furthermore to prevent the IPv6 addrconf: prefix with wrong length 48 to re-appear after future server reboots / boots the two sysctl values of course needs to be included in /etc/sysctl.conf e.g.:

debian:~# echo 'net.ipv6.conf.all.accept_ra = 0' >> /etc/sysctl.conf
debian:~# echo 'net.ipv6.conf.all.autoconf = 0' >> /etc/sysctl.conf
echo 'net.ipv6.conf.lo.autoconf = 0' >> /etc/sysctl.conf
echo 'net.ipv6.conf.eth0.autoconf = 0' >> /etc/sysctl.conf
echo 'net.ipv6.conf.eth1.autoconf = 0' >> /etc/sysctl.conf

My server has 2 etherhet interfaces, eth0 and eth1 that’s the reason I had to set up autoconf kernel the two vars net.ipv6.conf.eth0.autoconf and net.ipv6.conf.eth1.autoconf , for more interfaces more kernel vars (eth2, eth3) etc. needs to be set to “0”

I’ve seen posts online of people complaining about a similar errors to IPv6 addrconf: prefix with wrong length 48, like:

IPv6 addrconf: prefix with wrong length 96
IPv6 addrconf: prefix with wrong length 128

The solution to this messages is also done by setting the above described sysctl kernel vars. Setting the vars will suppress the messages which by the way with time could take up A LOT of disk space and fills /var/log/dmesg with this useless message, hence applying the “fix” is a must 😉

Another thing, I’ve noticed while I was researching about the error and the respective fix is that people on other deb based distributions like Ubuntu as well as on Fedora GNU / Linux had also experienced the issue.