Screencasting with OpenBSD
Any USB microphone should appear as a new audio device
uaudio0 at uhub3 port 4 configuration 1 interface 0 "Logitech USB Headset" uaudio0: audio rev 1.00, 6 mixer controls audio1 at uaudio0
audioctl can read off all of the specific characterisitcs of this device.
$ audioctl -f /dev/audio1 | grep record record.rate=44100 record.sample_rate=44100 record.channels=1 record.precision=16 record.bps=2 record.msb=1 record.encoding=slinear_le record.gain=127 record.balance=32 record.port=0x0 record.avail_ports=0x0 record.seek=0 record.samples=0 record.eof=0 record.pause=0 record.error=0 record.waiting=0 record.open=1 record.active=0 record.buffer_size=65536 record.block_size=4400 record.errors=0
Now test the recording using the sun:1 to specify audio device 1 using aucat(1)
aucat -m rec -f sun:1 -o file.wav
If the device also has a headset audio can be played through the same ddevice.
aucat -f sun:1 -i file.wav
Screen Capture using Xvfb
The rate at which a framebuffer for your video card is a feature of the hardware and software your using, and it's often very slow. x11vnc will print an estimate of the banwidth for the system your running.
x11vnc ... 09/05/2012 22:23:45 fb read rate: 7 MB/sec
This is about 4fps. We can do much better by using a virtual framebuffer. Here I'm setting up a new screen, setting the background color, starting cwm and an instance of xterm
Xvfb :2 -screen 0 800x600x16 & DISPLAY=:2 xsetroot -solid steelblue & DISPLAY=:2 cwm & DISPLAY=:2 xterm +sb -fa "Inconsolata" -fs 12 &
Much better! Now we're up around 20fps.
x11vnc -display :2 & ... 11/05/2012 18:04:07 fb read rate: 168 MB/sec
Make a connection to this virtual screen using raw encoding to eliminate time wasted on compression.
vncviewer localhost -encodings raw
A test recording with sound then looks like this
ffmpeg -f s16le -i /dev/audio1 -f x11grab -s 800x600 -i :2.0 -vcodec ffv1 out.avi
Screen Capture using Xephyr
Xephyr is perhaps the easiest way to run X with a shadow framebuffer. This solution also avoids reading from the video card's RAM, so it's reasonably fast.
Xephyr -ac -br -noreset -screen 800x600 :1 & DISPLAY=:1 xsetroot -solid steelblue & DISPLAY=:1 cwm & DISPLAY=:1 xterm +sb -fa "Inconsolata" -fs 12 &
Capture works in exactally the same way. This command tries to maintain 15fps.
ffmpeg -y -f x11grab -s 800x600 -i :1.0 -vcodec ffv1 ~/out.avi
If you find that the audio is way out of sync with the video, you can ajust the start using the -ss before the audio input to specify the number of seconds to delay. My final recording command line, that delays the audio by 4.3 seconds, writing 10fps
ffmpeg -ss 4.3 -f s16le -i /dev/audio1 -y -f x11grab -r 10 -s 800x600 -i :2.0 -vcodec ffv1 ~/out.avi
Sharring a Terminal with tmux
If you're trying to record a terminal session, tmux is able to share a session. In this way a recording of an X framebuffer can be taken without even using the screen. Start by creating the session.
tmux -2 -S /tmp/tmux0
Then on the remote side connect on the same socket
tmux -2 -S /tmp/tmux0 attach