Archive for the 'screencast' Category

Recording screencasts with ffmpeg

I had Istanbul running on dapper quite happily by building the edgy source package on dapper, but I can’t get Istanbul working reliably on edgy. The audio’s fine but the video flashes horribly. Now I somehow can’t replicate my Istanbul setup on another dapper machine…

So back to the drawing board to try other options… and I took the plunge with the patched ffmpeg. Not elegant as far as starting and stopping, but the quality’s great. It does mean I end up with the result in an avi file rather than ogg, but that’s easy enough to convert.

Then I use the following to get rid of the start and end where I’m operating ffmpeg – ss is the time to crop off the start, and t is the duration I want, cropping the rest off the end:

ffmpeg -i original.avi -sameq -ss 00:00:08.005 -t 00:00:55 the_video.avi

The only issue is that the file size goes through the roof – from 1.8MB to 5.1MB – still have to figure that out without degrading the quality…

Then I can convert to high quality FLV with:

ffmpeg -sameq -i the_video.avi the_video.flv

and compressed ogg with:

ffmpeg2theora cropped.avi

Now to try the patched ffmpeg on edgy…

Istanbul recording with external USB Audio

I’ve finally got decent audio for screencasts. I’m using istanbul on Ubuntu Edgy, and the sound quality for recording through a builtin soundcard is predictably terrible, even with a Shure SM58 hooked up through several adaptors to get from XLR to 3.5mm into the mic jack…

So bring on the M-Audio Duo, a USB mic preamp that we had used previously on a Windows 2000 machine. Will it work? Even on Windows it was a black art configuring recording through this device as it had a task tray thingy that let you choose different driver options – MME, WDM, EASI and ASIO, only one of which I could actually get working.

Switch it on, connected to my laptop, and I get a notification, “New audio device connected – To configure your new audio device Duo and possibly set it as default device, open System -> Preferences -> Sound.” with a helpful “Open audio preferences” to do just that. Cool!

However, the Sound preferences weren’t very helpful. I could select “USB audio” for output – that worked – or for input – impossible to tell… Audacity had a separate configuration, and worked fine recording from this device when I configured the input to “/dev/dsp1″ which appears when the Duo is connected and on.

Istanbul had no obvious way to select an input, so after much searching, I mailed Zaheer Abbas Merali, the primary Istanbul developer who mailed back this advice within half an hour:

Assuming you want to do this with alsa rather than oss. Run:
gstreamer-properties (can also get to it from Desktop, Preferences,
Multimedia Systems Selector) and set your default input plugin for
audio to custom and type: alsasrc device=hw:1.

Then Istanbul will record from the second sound device.

It worked! Now I’ve hooked up my Oktava MK319 which gets phantom power from the Duo, and the sound quality is excellent.

Update: Now if only Istanbul would record the video properly


Get every new post delivered to your Inbox.