datamoshing-mp4.rb

#!/usr/bin/env ruby
# Usage: ruby datamoshing-mp4.rb input.mp4 > output.mp4

def uint32 s
  s.unpack("C4").reverse.each_with_index.inject(0) { |r, v| r += v[0] << (v[1] * 8) }
end

input = ARGV.shift
data = File.open(input).read

s = data.split(/([\s\S]{4}stss[\s\S]{8})/)
points = uint32(s[1].slice(12, 4)).times.collect do |i|
  uint32(s[2].slice(i * 4, 4))
end

s = data.split(/([\s\S]{4}stco[\s\S]{8})/)
offsets = uint32(s[1].slice(12, 4)).times.collect do |i|
  uint32(s[2].slice(i * 4, 4))
end

points.slice!(0) # save the first keyframe
points.each do |p|
  b = offsets[p - 1]
  e = offsets[p]
  head = data.slice(0, b)
  body = "\000" * (e - b)
  tail = data.slice(e, data.size)
  data = head + body + tail
end

print data