correct aspect ratio of mp4 file without re-encoding

I wanted to correct the aspect ratio of an mp4 file without re-encoding. Videohelp.com forums had this question answered. In my case, the video was 640x268 pixels, and was supposed to be 4:3.

x * 640 / 268 = 4/3 ; So  (1/x) = 640 * 3 / 268 * 4 = 160 / 89, approximately = 16/9

So, my commandline was

mp4box -add inputfile.mp4#1:par=9:16 -add inputfile.mp4#2 output.mp4

One caution - temp file seems to be created in the default Windows temp folder, or perhaps in the same folder as the input file - did not verify which. Overall operation takes as much time as two copy commands - "importing" and "writing" done separately.

dicom viewers

idoimaging.com lists a whole lot of DICOM and other image format viewers. Searching there for viewers which do 3D volumetric rendering, found 3dimviewer - capable and free. 

testing website before changing DNS

Testing websites before changing the DNS - this is something which I need to do often. I've relied on the Telnet based method in the past. But when the content needs to be checked, it's better to do the hosts file based method. Dreamhost has good documentation on this, and also on flushing DNS.

So, on Windows XP, edit C:\Windows\System32\Drivers\etc\hosts
and run

ipconfig /flushdns

Will need to restart browser after flushing dns cache, too. 

Oculus Rift trials

Finally a post on the Oculus Rift DK2. I had tried out Google Cardboard earlier, and wanted to see how much better the Rift is. Unfortunately the system specs needed are very steep. Smooth 70 fps+ framerates were obtained only on a machine with the following specs, which costs more than Rs. 2 lakhs:

A Mac Mini was not enough - the frame rate was 10 fps for the Tuscany Demo. A few of the Rift demos I sampled were the following:

Short notes:
VRSurgery - view is like a big screen tv with a wide field of view.
3d gallery - interesting and works OK.
HiyoshiJump - a simple demo
bungee - no hmd detected - probably this does not work with DK2
surface of mars - an OK demo
spacewalk - limited?
Malfunction - hmd?
mars walk - field of view not as good as "surface of mars"
chair in a room - an OK demo
earthvr - needs a good internet connection and good specs for the machine
roculus - a lo res demo
vrspacetunnel - wrong registration - probably doesn't work with DK2
Titans of space worked at 15 fps on the Mac Mini
Unity demo - at 10 fps on the Mac Mini
Trying a fisheye movie Cosmic Colors on liveviewrift - not very clear focus, equirec mode
vrplayer not available for Mac, so can't do a head to head comparison with Google Cardboard.
Edit - KolorEyes player is available for both Cardboard (Android) and Oculus. Renders well.

My conclusion of Rift vs Cardboard - Cardboard's strength is affordability -smooth display, no rendering lags on low cost hardware. With a powerful machine, Rift shines due to configurability, input methods, hand tracking possibilities, etc.