James Hensman’s Weblog

May 15, 2009

Making and Breaking Videos into pngs

Filed under: Uncategorized — jameshensman @ 10:59 am

I’ve got some videos that I’d like to do a little bit of processing on. nothing spectacular, I just want to track a black blob.

Luckily numpy/Scipy has all the tools I need to get started… on images. I need to break the (avi) video file into a series of png files (i could use jpeg, I suppose, but it’s not like hdd space is limited here…). The tool I’ve been using for this is ffmpeg.

Now, ffmpeg is a phenomenal beast. It can re-scale videos, re-encode them, crop them, and all kinds of other things that I’m not interested in. The command I’ve used to break a avi file into pngs is:

ffmpeg -i ./tmp/%03d.png

It’s nice that ffmpeg recognises the %03d format string, huh? Now that I’ve got some images, I can load them into numpy and process them (future blog post!)

After doing said processing, ffmpeg should be able to re-code my processed images into a video file for convenience. However, I’m really lazy, and can’t be bothered to read the whole of the ffmpeg doc. So I’m copying Mike here and using:

mencoder ‘mf://tmp/*.png’ -mf type=png:fps=10 -ovc lavc -lavcopts vcodec=wmv2 -oac copy -o <whatever>.mpg

I’m sure ffmpeg can do the job too, but it just isn’t working for me.

In fact, I’m wrapping both of those commands up in python, using the os module.


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