Low-Latency Live Streaming your Desktop using ffmpeg

I recently bought myself a projector, which I installed in one corner of the room. Unfortunately I didn’t buy a long enough HDMI cable with it, so I could not connect it to my desktop computer and instead used my loyal ThinkPad T60 for playback. But I also wanted to be able to play some games using the projector, for which my laptop wasn’t beefy enough. So I thought, why not just stream the games from my desktop computer to the laptop?

In this post I will explore how to stream 720p (or any quality for that matter) from one computer to another using ffmpeg and netcat, with a latency below 100ms, which is good enough for many games. TL;DR; If you don’t care about the technical details, just jump to the end of the post to try it out yourself.

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QCAD – Symbols, special characters and font styles in dimension labels

Cover - QCAD with Alpha and l_ABz dimensions

QCAD is a great free and open source CAD software. Although limited to 2D design, it is my favorite tool for drafting, construction and simple sketches. It is well documented overall, but one issue I could not find a solution for, was how to label dimensions with symbols, special characters or certain font styles (bold, italic, super-/subscript).

This blog post provides a simple trick to get it done.

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Maxima (software) and gnuplot – plot functions using lines with symbols on it (workaround)

maxima-title-workaround

I am recently working on some scientific papers for which I have to visualize a lot of mathematical functions. In a good scientific paper the graphs (and visualizations in general) should be colorless and utilize dotted/dashed lines or lines with symbols on it instead of colors. This has several advantages: A colorless plot is more neutral to the reader, he/she does not get distracted by the different colors. A reader may also have a (subliminal) preference in color, so he/she pays more attention to e.g. the red curve than the yellow one, that is hardly readable on the white background anyway. This also helps to distinguish functions, if they are plotted in one diagram and printed in gray scale mode or read by color blind people. Also, if two identical functions are plotted in one diagram, using just colors will probably only show one of the functions and hide the other.

I am using the CAS software Maxima to do the calculations, which in turn uses gnuplot to plot the functions. Gnuplot alone does the job perfectly. However, when plotting functions (and not discrete data points) using lines with symbols on it from within Maxima (which also uses gnuplot to plot the graphs), the results are quite ugly. There seems to be no proper solution to this problem.

This blog post suggests a workaround that is rather ugly, but which produces very nice graphics, that meet the above-mentioned requirements.

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Samsung SSD 840 EVO 2.5 Zoll SATA – Firmware update under GNU/Linux

I recently bought a Samsung SSD to replace my HDD in my Arch Linux notebook. It is a “Samsung SSD 840 EVO 2.5 Zoll SATA”. One of the first things I do when I get new hardware is to make sure the latest firmware is installed. Mine did not have the latest firmware update and – as it was to expect – Samsung SSD firmware updates under GNU/Linux are not (officially) supported. Samsung ships only Microsoft Windows software, called “Magician”, which can directly update the firmware or create a live USB-Stick to do the update. Additionally, they provide *.iso image files (one for Microsoft Windows systems and one for Apple computer, respectively) to update the firmware from a live CD. The *.iso image file intended for Microsoft Windows would also work under GNU/Linux, only that my notebook does not have a CD Drive anymore. Obvioulsy, the only option left was to create my own live USB-Stick under GNU/Linux – without using Microsoft Windows and that crappy Samsung “Magician” software. A simple “dd” comand to “burn” the *.iso file on an USB-Stick did not do the trick, as the Isolinux version Samsung uses is over 10 years (!) old.

This article shows how to update the firmware of a “Samsung SSD 840 EVO 2.5 Zoll SATA” under GNU/Linux using a bootable live USB-Stick.

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Create a GNU/Linux multiboot USB-Stick (Live USB) with Syslinux chainloading

Since USB-Sticks, that are fast and have a high capacity, are finally affordable, I decided to buy a new one. I usually install a GNU/Linux live CD (more precisely live USB) distribution on my USB-Sticks: either SystemRescueCd or Kali Linux (former Backtrack). The left over space is used for the classical purpose of an USB-Stick – data exchange. Todays USB-Sticks have enough capacity to easily fit several GNU/Linux live distributions on them, while still leaving enough space for other data. So my plan was to create a multiboot USB-Stick, that would boot my favourite GNU/Linux live distributions mentioned above. Unfortunately, searching the internet for implementing this did not give me any satisfactory results. There are a ton of guides that explain how to create an USB-Stick that boots GNU/Linux, but there are almost no multiboot solutions. The few howto’s about multiboot USB-Sticks are either about booting *.iso files (which only works with some GNU/Linux distributions) with GRUB 2 (which is designed for static boot setups anyway) or require further customized modifications of the GNU/Linux live distributions. I wanted a simpler solution that – once created – allows for easy updating of the installed GNU/Linux live distributions.

This guide will explain how to create a multiboot USB-Stick that can boot several GNU/Linux live dirstibutions via Syslinux chainloading. It will have several partitions (one for each OS and one for the main Syslinux bootloader) and a separate data partition, that can be formated independently in any way you like, so that your data is seperated from the operation system data. This guide installs SystemRescueCD and Kali Linux on your multiboot USB-Stick, but any other GNU/Linux live distribution should work as well. Adding more than two OS should also be no problem.

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How to install and configure CherryMusic on a Debian Wheezy (headless) server

cherry_music_web_notextplusopenlogo

This guide explains how to correctly — and more importantly cleanly — install CherryMusic on a (headless) server running Debian Wheezy — without polluting the operating system in any way. For Arch Linux or a more generic installation see the CherryMusic Arch Linux wiki page and CherryMusic’s own wiki on GitHub.

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The “Matrix Code” in your linux terminal using python and curses

Everybody knows the code on the screens in the movie the matrix. You can see it for example when the character “cypher” talks to “neo” somewhen in the night, and the green letters fall down on those second-hand dell screens behind them. Funky. I want that too.

cypher_neo_code

I’ve written a python program that uses curses to create a similar looking animation and just now cleaned up the code a bit and made sure it runs in python 2 and 3. You can get the source code on github and there’s a screenshot and a short explaination after the break…

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PyLint and Pep8 validation in geany

If you’re into python, but don’t know about PEP8 or PyLint, you should find out right now. And because pep8 and pylint are great, but it’s hard to force yourself to use them all the time, lets integrate them into geany, a fast and lightweight IDE.

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Indexing large tar files for fast access using python

I recently needed to get some data out of a large tar file, about 5gb in size, that I didn’t want to extract, as it contained many thousands of small files. Unfortunately the tar format was not designed to be indexed, since it was meant for backups on magnetic tapes (tar stands for tape archive). The gnu tar has a command for retrieving single files, but it needs to go through the whole tar each time, which was just too slow.

So I decided to write a little tool, that would index all files inside the archive and write that index to another file. Now I can access each file within the tar in just a second, instead of 15 minutes. Introducing the tarindexer!

UPDATE: The project is now up on github under GPL v3
https://github.com/devsnd/tarindexer

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Android ADB over Bluetooth

Today I had no WiFi. And no USB cable. So I figured out a way to use ADB over bluetooth, because no one can stop me from developing an App. It is a rather simple hack, which should work on any rooted phone (or tablet).

All you need is a terminal emulator for android, and a bluetooth capable linux computer, of course.
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