Datamoshing step-by-step.

http://ubuntuforums.org/showpost.php?s=72cb530ab96ddb3e8c37f8f987daddfb&p=9310507&postcount=4

it's pretty easy:
you can for example use ffmpeg and avidemux.
first you convert your input file with ffmpeg:

	ffmpeg -i infile.flv -g 500 outfile.avi

the -g option specifies keyframes (which is what he does at around 2.50).
the number he specifies is way too high, and you will get an error if you try this with ffmpeg (999 is still too high but gives no fatal error).
this leaves you with an outfile with very few (for shorter files just a single) i-frames.
you can then make another file with the same procedure.

then loading the first file into avidemux you can append the second one just as the guy with the pandas does and delete its i-frames by manouvring with the double-arrrows.