Shivam ShivamJoker

FFmpeg cheat sheet

A list of useful commands for the FFmpeg command line tool.

Download FFmpeg: https://www.ffmpeg.org/download.html

Full documentation: https://www.ffmpeg.org/ffmpeg.html

Basic conversion

Install and use pip on macOS without sudo / admin access

Most recently tested on macOS Sierra (10.12.6)

Download the installation script; curl https://bootstrap.pypa.io/get-pip.py -o ~/Downloads/get-pip.py
Run the installation, appending the --user flag; python ~/Downloads/get-pip.py --user. pip will be installed to ~/Library/Python/2.7/bin/pip
Make sure ~/Library/Python/2.7/bin is in your $PATH. For bash users, edit the PATH= line in ~/.bashrc to append the local Python path; ie. PATH=$PATH:~/Library/Python/2.7/bin. Apply the changes, source ~/.bashrc.
Use pip! Remember to append --user when installing modules; ie. pip install <package_name> --user

Note

How to add a collapsible section in markdown

1. Example

Click me

Heading

Foo
Bar
- Baz

Qux

While a lot of Node.js guides recommend using JWT as an alternative to session cookies (sometimes even mistakenly calling it "more secure than cookies"), this is a terrible idea. JWTs are absolutely not a secure way to deal with user authentication/sessions, and this article goes into more detail about that.

Secure user authentication requires the use of session cookies.

Cookies are small key/value pairs that are usually sent by a server, and stored on the client (often a browser). The client then sends this key/value pair back with every request, in a HTTP header. This way, unique clients can be identified between requests, and client-side settings can be stored and used by the server.

Session cookies are cookies containing a unique session ID that is generated by the server. This session ID is used by the server to identify the client whenever it makes a request, and to associate session data with that request.

*S

Install mosquitto with websockets

This is a guide how to install mosquitto on Ubuntu with websockets enabled.

It is more or less the same as explained in the article "Six Steps to install mosquitto 1.4.2 with websockets on debian whezy" http://www.xappsoftware.com/wordpress/2015/05/18/six-steps-to-install-mosquitto-1-4-2-with-websockets-on-debian-wheezy/comment-page-1/

Exceptions:

mosquitto version 1.4.10 is used.

	<html>
	<body>
	<h4>websocket</h4>
	<h5>Group: <span id="group">darwin</span></h5>
	<!-- a hardoced group name -->
	<button onclick="bjoin();">join group</button><br>
	<input id="text" type="text"/>
	<span id="out"></span>
	<script>
	var group=document.getElementById("group").textContent;

	#!/bin/bash

	TABLE_NAME=TableName
	KEY=id

	aws dynamodb scan --table-name $TABLE_NAME --attributes-to-get "$KEY" --query "Items[].id.S" --output text \| tr "\t" "\n" \| xargs -t -I keyvalue aws dynamodb delete-item --table-name $TABLE_NAME --key '{"id": {"S": "keyvalue"}}'

	/**
	* Encrypts plaintext using AES-GCM with supplied password, for decryption with aesGcmDecrypt().
	* (c) Chris Veness MIT Licence
	*
	* @param {String} plaintext - Plaintext to be encrypted.
	* @param {String} password - Password to use to encrypt plaintext.
	* @returns {String} Encrypted ciphertext.
	*
	* @example
	* const ciphertext = await aesGcmEncrypt('my secret text', 'pw');

	#!/bin/bash

	USER=${1:-sebble}

	STARS=$(curl -sI https://api.github.com/users/$USER/starred?per_page=1\|egrep '^Link'\|egrep -o 'page=[0-9]+'\|tail -1\|cut -c6-)
	PAGES=$((658/100+1))

	echo You have $STARS starred repositories.
	echo

	#!/usr/bin/env python3

	"""
	Get reading from Nova PM Sensor SDS011
	(dust sensor, air quality sensor, PM10, PM2,5)

	Designed to run from cron and append CSV file.

	Script tested using Python3.4 on Ubuntu 14.04.