FFmpeg 3.0.12
Since* 0.7
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Damages the contents of packets without damaging the container. Can be used for fuzzing or testing error resilience/concealment.

Parameters: A numeral string, whose value is related to how often output bytes will be modified. Therefore, values below or equal to 0 are forbidden, and the lower the more frequent bytes will be modified, with 1 meaning every byte is modified.

ffmpeg -i INPUT -c copy -bsf noise[=1] output.mkv

applies the modification to every byte.