Apply low pass and high pass frequency filter using ffmpeg

Just a quick example that applies both a high pass and a low pass frequency filter to a video file using ffmpeg

ffmpeg -i input.mp4 -filter:a "highpass=f=200, lowpass=f=3000" output.mp4;

The frequency is set in Hz so in this example we are filtering out all frequencies that are out of [200, 3000].

Remove all non digit characters from String

The following Java snippet removes all non-digit characters from a String.
Non-digit characters are any characters that are not in the following set [0, 1, 2, 3, 4 ,5 ,6 ,7 ,8, 9].

myString.replaceAll("\\D", "");

For a summary of regular-expression constructs and information on the character classes supported by Java pattern visit the following link.

The \\D pattern that we used in our code is a predefined character class for non-digit characters. It is equivalent to [^0-9]that negates the predefined character class for digit characters [0-9].


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The blue filter observed in this picture is the Electric filter from the Prisma application of Prisma Labs.

Prisma is a photo-editing application that utilizes a neural network and artificial intelligence to transform the image into an artistic effect.
— From Wikipedia:

The scary looking creature photographed is a fictional character from the Warcraft franchise and it is called a Murloc:

The murlocs are amphibious bipedal fish-like creatures, which dwell along the coastlines of the Eastern Kingdoms, and few other locations. Little is known about this species, although they seemingly have enough intellect to form societies and tribes, even having their own faith system. They have their own spoken language, although it is unpronounceable in the common tongue.
— From Wikipedia:

Useful links:

In this gallery we added along with the original and the filtered pictures some more that use half of the original picture and half of the filtered picture to better show how the effect altered the original picture.


  • Prisma only accepts square images and it will resize the produced result to 1080px if the input image is larger than that.
  • The creation of the mixed images was done manually using Gimp.
  • We added the text at the end of the images using the following set of commands on a GNU/Linux environment (specifically Fedora) using bash shell and the imagemagick suite:
mkdir "$folder";
for img in *.jpg;
  width=`identify -format %w "$img"`;
  convert -background '#0008' -fill white -gravity center -size ${width}x30 caption:"©" "$img" +swap -gravity south -composite "./$folder/$img";

The filtered images were added to the sub-folder called “modified” while the original images were not changed at all.