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看到一个老外的博客上写的。自己没试过。
以前在Linux上用ffmpeg的x11grab选项来录屏。录制过程没有问题，但是后期转码的时候做出来的mp4文件体积非常大。一直没找到好的解决办法（对ffmpeg以及视频的编码解码不太熟悉）。

http://eradman.com/posts/screencasting.html
作者： Eric Radman

Screencasting with OpenBSD

USB Audio
Any USB microphone should appear as a new audio device. Here is the dmesg for my mic by ART:

uaudio0 at uhub0 port 2 configuration 1 interface 0 "M-One USB" rev 1.10/0.01 addr 2
uaudio0: audio rev 1.00, 8 mixer controls
audio1 at uaudio0

audioctl can read off all of the specific characterisitcs of this device Now test the recording from the second audio device using aucat(1) If the device also has a headset audio can be played through the same device. 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 Much better! Now we're up around 20fps. Make a connection to this virtual screen using raw encoding to eliminate time wasted on compression. A test recording with sound then looks like this Note: always stop the recording and playback using q, not Ctrl-C so that audio inputs are shut down properly.

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. Capture works in exactally the same way. This command tries to maintain 12fps. To capture keyboard and mouse input press Ctrl then Shift. This is very handy for using navigating a window manager in the nested X session.

Arranging Windows

I have sometimes found it helpful to launch applications and arrange them in a specific way. This will open up a web browser listing the current directory and position windows using xdotool This will position the window precisely so that it appears to be in a tmux window on the right.

Audio/Video Sync
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 0.5 seconds, writing 12fps 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. Then on the remote side connect on the same socket Taking Screenshots
Grabbing a screenshots on Xvfb server is easily accomplished with ImageMagick's import command Audio Processing and Video Transcoding
The first step is to ensure that the clip begins and ends where you'd like it to. The following will make a copy of the recording starting at time 00:00 and ending at 09:45 Setting the gain correctly is very important with an analog mixer, but if you're using a USB mic there may not be a gain option; simply record using it's built-in settings and then adjust the levels afterwards using a utility such as normalize. First extact the audio as a raw PCM file and then run normalize Next merge the audio back in again The final step is to compress the screencast for distribution. Encoding to VP8/Vorbis is easy: H.264/AAC is tricky. For most video players the color space needs to be set to yuv420p. The -movflags puts the index data at the beginning of the file to enable streaming/partial content requests over HTTP: