Recording QEMU’s VNC output to a flash file

First off it doesn’t do sound… I’ll have to search further for something that will let me do something more.. involved, but for now, this works well enough.

First I’m going to use Qemu 0.14.0 for this, earlier ones will work, but if it’s too old, there isn’t any support for VNC output. I figured I’d start with something simple, Lemmings, from the Win32s demo a while back. Now VNC doesn’t like it when you change resolutions, so I find it’s best to start out in the video mode you plan on recording. So once the VM is fired up I go ahead and load Windows. Qemu can support multiple outputs so I’m going to specify that it listens on the default VNC port (TCP 5900), and bind it to my IPv4 loopback. I’m also going to open up the SDL Window, because I like to see what I’m doing. If you want to get more sophisticated, you can even use a multiplexer program like VNC Reflector which will allow multiple people (or programs) to connect to the VNC port.

qemu -L pc-bios -m 32 -hda win31.qcow2 -vnc -sdl -soundhw sb16,adlib

Now a minor word about audio.. I am currently having issues aligning this up.. no doubt I’m doing something wrong, or I should just break down and use some proper editing tools but it kind of works for now. Also to get a ‘clean’ capture of the audio from the VM, I use Virtual Audio Cable. By simply changing my default sound device to a VAC, and my default Mic to the same VAC I don’t have to worry about background noises, or anything else. Not to mention in Vista or Windows 7, you can mute other programs so you won’t have instant pestering bleeding into it.

I’m using the awesome program vnc2flv to record this. Now it is a python program, but thankfully us windows users don’t have to go through too much hell to run this, I just downloaded it from ‘RT’s Free Software‘.

I just kick it off like this:

flvrec -C 640×480+0+0 -o video.flv

And it’ll start recording. I then kicked off sox to record the audio like this:

sox -4 -b 16 -d audio.wav

Then once I’m done doing what I’m going to record, kill both programs.

While sox can record mp3’s if you find libmad, or build it yourself, I found it was just easier to use lame.

lame -r -x -s 44.1 –bitwidth 16 audio.wav

And yes, you *DO* need to output at 44100Hz or 44.1Khz for the audio. Any other level and you can’t combine the flv & audio. Yes I tried and tried, but don’t fight it, and thank me for finding the flags to pass to lame.

Then use flvaddmp3 to combine the audio and the flv video into a final.flv.

flvaddmp3.exe video.flv audio.wav.mp3 final.flv

Now you can upload it to youtube, and from there embed or share it as you wish.

I had originally used pyvnc2swf, which will create a flash file directly, however it doesn’t deal that well with screen refreshes. But if anyone wants to use it, remember the default VNC port is 5900, and you must pick a file to ‘save as’ first then you can start the recording. Also in things like windows, I found having notepad open to full screen then minimizing it was a good way to force a screen redraw.

2 thoughts on “Recording QEMU’s VNC output to a flash file

  1. I usually use VirtualDub's screen capture mode to record Qemu sessions (and VMWare with 3D acceleration enabled). With the ZMBV codec from DosBox getting 60FPS 1280×720 video with less than 1 dropped frame per minute works really nicely (just remember to set the video format to RGBA, otherwise ZMBV won't work).

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