Thursday, August 19, 2010

Video Time Compression with VirtualDub

If you are like me you have probably wanted to do some video time compression of some video in the past but have never been able to justify the cost of the fancier programs that were set up to do. I have found the answer for both of us and it is free.

I had used Virtualdub in the past but could never figure out quite how to do it correctly until tonight. I took a simple HD video that was laying around that I had shot back in July with my Pentax K-7 hoping to get some good lightning strikes and tossed it in Virtualdub and got some pretty good results. The video was originally 3:14 long and was cut to :24.

Grab you a copy of Virtualdub if you don't have it and lets get started. Open up Virtualdub and drag your file into the window and drop it in and you should see something like this:

Then click on video in the menu and select "Frame Rate" like so:

Now here is the part you will have to consider but myself I went with an 8 to 1 ratio. If you want to speed up your video then multiply your frame rate by the rate of speed you want to compress it by (30 times your desired ratio) and enter it in the "change frame rate to (fps)" box and then enter the same multiplication factor in the "decimate by" box. Make sure you clicked the correct selections as shown below and click OK.

Some people will do a 4X rate and in that case you would have a "120" frame rate and a decimation factor of "4". In my case I wanted an 8x speed and so I ran a "240" frame rate and a decimation factor of "8" as shown in the next screen:

At this point you can go ahead and save the AVI file but it will be huge and need compressed. With the right codecs installed you can also do that under the video option as well by clicking
the appropriate codecs before saving the file.

Click File / Save as AVI and let it run out your new time compressed video.

It is that easy. Just remember that if you don't use some kind of compression codecs in Virtualdub that the file will be huge and will need to be compressed with another program after the fact.

Jim Saueressig -

1 comment:

  1. This isn't correct. Not at all. Most computers cannot process the frame rate you're using, even if you decimate it by 8. What you'll end up with, especially with people using WMP is a lot of dropped frames or video that skips. The trick to time lapse is to lower the converted frame rate to something low like 10 or 15fps, and the playback frame rate to a max of 60 or 120. Then save, and then reprocess the video back to 30 frames per sec so that its playable on all machines. HD Video especially. You simply cannot to time lapse you method with HD video.