Category Archives: Linux

Creating animated gifs in Ubuntu

Something that I do for a lot of my posts is create animated gifs, and usually I forget the whole process and have to re-look up everything. So here I will consolidate the process. There are four steps: 1) record video; 2) convert to images; 3) trim down image set; 4) convert to gif.

First, I’ve had luck recording the original video using the SimpleScreenRecorder program. Installation instructions are on their homepage, it’s very simple. I had been using RecordMyDesktop and tried Kazam, but prefer SimpleScreenRecorder.
Once you have your video, create a folder to store all your images in.
I called mine ‘images’.

To convert the video to a set of images we’ll need mplayer. In linux to install this it’s just

sudo apt-get install mplayer2

Once you have mplayer installed, change directories into your images folder and run

mplayer -ao _ ../movie_name.mp4 -vo png:z=9

This will fill up the folder with a bunch of screenshots from the video.

At this point you can go ahead and convert these images into an animated gif, but I always trim down the set to reduce the gif size. This just entails me going through and deleting every other image until I get a file that’s less than a megabyte. Once you’ve got the image set that you want to convert, you’re going to need ImageMagick installed. If you don’t have it, just run

sudo apt-get install imagemagick

Once you have that you’re going to use the convert function:

convert -delay 10 -loop 0 -deconstruct -quantize transparent -layers optimize -resize 400x400 *.png animation.gif 

with a bunch of extra options attached to control the play speed (that’s the delay parameter), the looping, some optimization parameters, and then what size it comes out (I’ve chosen 400×400 pixels here).

And there you go! You can now create your own fancy gifs.

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Getting function run time in C++ on Linux

I wanted to time how long it took for one of my functions to run yesterday and it ended up taking me a little bit of time to track down how to do this in C++ on a Linux box, so I thought I’d throw up the code here.

#include <sys/time.h>
#include <iostream>
using namespace std; 

int main() { 

    struct timeval start_time; 
    struct timeval end_time; 
    gettimeofday(&start_time, NULL);
    aFunction(someParams); // function to be timed
    gettimeofday(&end_time, NULL); 

    // get difference, multiply by 1E-6 to convert to seconds
    float duration = (end_t.tv_sec - start_t.tv_sec) + (end_time.tv_usec - start_time.tv_usec) * 1E-6; 
    cout << "duration: " << duration << "s" << endl;

And that’s it! Not too much to it, but was a little difficult to track down.

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