Well, in this post I’d like to review the equipment that’s in this lab. I’ve started to put together some documentation on how to assemble, use, and process the data out of the usability lab. This is really just an excerpt of the Assembly Instructions document I started writing in the Fedora wiki:

1. Carrying case – it’s an Opteka equipment case, with foam padding on the inside, cut out to create various fitted components for the parts. Here’s a photo showing all the parts in the case.
2. Microphone and microphone plate – it’s a crown omnidirectional mic. The pickup really isn’t that great, so I’m going to be looking to either get some phantom power for it or maybe replace it with a better one at some point.
3. D-SUB connector video cable (for scan converter) – this connects the input of the scan converter to the output of the computer you’re running the tests on, so that the DVR can record the desktop. This means all desktop recording is done externally from the computer, so your usability tester won’t notice any lag or sluggishness due to recording.
4. Scan converter USB power cable – this whole lab requires 6 power outlets, so thankfully the scan converter doesn’t require one more. It simply powers off of a USB port on your testing computer.
5. Scan converter box – the scan converter takes the video out of your testing computer (up to 1024×768) and turns it into a signal the DVR can record.
6. Camera AC power supplies (3) – the cameras are externally-powered by these.
7. Camera stands (3) – these screw into the bottom of the camera cylinders and are directionally adjustable.
8. Cameras (3) – these are Sony color security cameras and have very good pickup in dark conditions.
9. Camera BNC & power cables (3) – these are 10 feet long – a bit too long to be honest – but they get the job done, connecting the cameras to the back of the DVR.
10. Video cable for scan converter (RCA / BNC) – this allows the scan converter to send signal to the DVR. One end has a BNC converter to go into the DVR end.
11. DVR / video mixer – this is an AverMedia AverDigi SATA+ embedded Linux security DVR unit. It takes the signal from the three cameras and scan converter as well as the microphone and handles the recording of those into video files. As discussed previously, the file formats output by this little beastie are a bit of a pain, but GStreamer comes to the rescue and transforms this box into a workable solution. (By the way, here’s what the ports on back look like.)
12. DVR power supply – power for the DVR.

• DVR Remote (missing from image above)

For a fuller run-down of the equipment as well as a listing of additional needed equipment see: https://fedoraproject.org/wiki/Design/UsabilityLab/Assembly_Instructions. By the way, the specs and pricing for the parts listed above are also available on the Fedora wiki now, but I do intend to clean up that page to be a little more useful / readable in the future.

Thanks to all the folks who responded so quickly to help out on my last blog post! Because of your help, a bug got filed and fixed upstream in gstreamer, and a new build of gstreamer containing the fix for Fedora is on the way.

So I bet you were wondering why I was so interested in getting AVF videos into gstreamer, right? Well, I’m going to tell you anyway.

I’m in the process of putting together a portable usability testing lab. The key component to this usability testing lab is a quad-video-input video mixer / DVR unit. It can be hooked up to 3 cameras and one scan converter so you can have 3 panels of the user / testing environment and one panel showing the screen of the system they’re using. The particular unit I decided to get is the AVer Media AVerDiGi EB1304NET SATA+.

Now, there are a couple quirks to the EB1304. The first I noticed was that its audio input/output jacks are, well, a little unique:

Yes. It takes bare wires with little metal clips. I haven’t tested it yet, but the fine technical support folks at CCTV Wholesalers (who, by the way, I highly recommend for price, shipping speed, and speedy & helpful support) assure me it’ll work, so that’s something I’ll be testing out soon.

The second quirk, of course, is more crucial to the usefulness of the unit – the video files it outputs. While this little unit is an embedded Linux product (woo!), the file formats it produces unfortunately are not so open & standard. As I mentioned in my previous blog post about AVF files, it provides you with both an AVF (which is really just an AVI file with a slightly tainted header) and a TBL file for each of the four input videos. Now, these play fine in mplayer, vlc, and very soon gstreamer-backed players, but, one of the reasons I want to capture four videos at once is to produce usability testing videos that show both what the user is working on and their reaction, ideally a single video with all four inputs in a quad-split screen. AVer Media provides a CD-ROM with a bunch of Windows-only programs to do this in software – and they don’t even run in Wine. So, I wanted to try to get the AVFs working in gstreamer so that I could use gstreamer pipelines to achieve this quad-split video.

Well, since the updated gstreamer for Fedora wasn’t yet available this morning, I took Nicu’s advice and used mencoder to convert the AVF files to AVI:


mencoder -oac copy -ovc copy -o ch1.avi 2009_08_25_21_07_59_ch1.avf


Next, the ever-amazing Ray Strode hacked on putting together the gstreamer pipeline necessary to stitch them together into one video:


gst-launch -v filesrc location=ch2.avi ! decodebin ! videoscale ! video/x-raw-yuv,width=720,height=480 ! videobox left=-720 top=-480 border-alpha=0 ! videomixer name=right ! videomixer name=three ! videomixer name=all ! alpha ! ffmpegcolorspace ! theoraenc ! oggmux ! filesink location=all.ogv filesrc location=ch1.avi ! decodebin ! videoscale ! video/x-raw-yuv,width=720,height=480 ! videobox border-alpha=0.0 left=-720 ! alpha ! ffmpegcolorspace ! all. filesrc location=ch4.avi ! decodebin ! videoscale ! video/x-raw-yuv,width=720,height=480 ! videobox border-alpha=0.0 top=-480 ! alpha ! ffmpegcolorspace ! three. filesrc location=ch3.avi ! decodebin ! videoscale ! video/x-raw-yuv,width=720,height=480 ! alpha ! ffmpegcolorspace ! right.


AWESOME, right? Here’s the result, although I took the video of me out and replaced it with another copy of the screen video because I’m shy :

Download in OGV format

As we go through this process, I’m making sure to document everything so anybody else who wanted to put together a similar kit without having to run proprietary software to do so can learn from this experience. One of my next blog posts is going to be a rundown of all of the equipment I ordered for our kit with photos and writeups of how to use it all so if you are interested in this, you can look forward to that.

Next up is figuring out that little beastie of an audio input and then updating the pipeline to handle the audio. Wish me luck!