## How to Modify Video Speed with ffmpeg?

For Faster video speeds use: ffmpeg -i input.mov -filter:v “setpts=0.5*PTS” output.mov For Slower video speeds use: ffmpeg -i input.mov -filter:v “setpts=2*PTS” output.mov Note the factor multiplying PTS. If that factor is less than 1, then you get a faster video. The opposite otherwise. Thanks to: Modify Video Speed with ffmpeg

May all the best that time and chance have to offer be yours – Jeff Bendock: friend, mentor, and role model. Today (Aug 10) my wife and I went through an extraordinary experience. But what we experienced was not unique. We’re not the first or last people to experience it by any means. There was …

## Vector Graphics Plots using Matplotlib in Jupyter

Here’s a neat trick I learned today to display all matplotlib plots as vector format rather than raster in Jupyter notebooks:

## nbviewer and gitlab

You can view your (public) jupyter notebooks hosted by gitlab using nbviewer by changing the “blob” work in the hyperlink to raw.

## Convert IPython Notebook to Slides

Convert and display in place: jupyter-nbconvert –to slides mynotebook.ipynb –reveal-prefix=reveal.js –post serve Convert to html: jupyter-nbconvert –to slides mynotebook.ipynb –reveal-prefix=reveal.js as always, try: jupyter-nbconvert –help

## Jupyter Notebook doesn’t Automatically Open a Browser on OS X

This issue appears to have showed up on Sierra. Here’s a simple fix: Edit your bash profile (emacs ~/.bash_profile) Add export BROWSER=open Close your shell or source it (source ~/.bash_profile) Things should get back to normal now. Ref: https://github.com/conda/conda/issues/5408

## Copying Lists in Python

make sure you don’t fall into the trap of copying pointers in Python: import numpy as np a = np.zeros(2) print(“a = “, a) b = np.zeros(2) print(“b = “, b) b = a # this assignment is simply a pointer copy – b points to the same data pointed to by a a[0]=33.33 # …

## How to Highlight Code in Keynote

First install a utility called highlight. It is available through macports and homebrew. sudo port install highlight Now that highlight is installed, you can “apply” it to a file and pipe it to the clipboard: highlight -O rtf MyCode.cpp | pbcopy Now go to Kenote and simply paste from clipboard (or command + v). Highlight …

## C++ – Calling Overloaded Operator () from Pointer

Here are three ways to call a C++ classes’ operator () using a pointer: Say you have a C++ class name MyClass that overloads the operator “()”, something along the lines: I use method 2.

## Convert Movie or Animation to Animated Gif

mkdir frames ffmpeg -i input -vf scale=320:-1:flags=lanczos,fps=10 frames/ffout%03d.png convert -loop 0 frames/ffout*.png -fuzz 20% -layers OptimizePlus output.gif Thanks to: http://superuser.com/questions/556029/how-do-i-convert-a-video-to-gif-using-ffmpeg-with-reasonable-quality

## Unbounded Kinetic Energy in Forward-Euler Inviscid Flows

Observation When using a forward-Euler method for the time integration of the momentum equation for an inviscid-flow, it appears that the kinetic energy of the flow grows unbounded in time, regardless of the timestep size. Problem Statement Estimate the change in total kinetic energy when using forward-Euler to integrate the Euler momentum equations in a periodic box. Approach To …

## List and Sort Files by Size

Find and sort all files > 1Mb in size, in current directory and subdirectories find . -size +1M -exec du -h {} \; | sort -nr

## Some Regex Notes

I happened to be dealing with a bunch of mallocs that look like this double* f =  (double*)malloc(sizeof(double)*nx*ny*nz); double* g = (double*)malloc(sizeof(double)*nx); double* h = (double*)malloc(sizeof(double)*nx*nz); I wanted to convert all of those those to use new, i.e. double* f = new double[nx*ny*nz] Using regex made all this possible search for: $$double\*$$malloc$$sizeof\(double$$\*(.*)\) replace with: new …