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• Howto merge two avi files using ffmpeg ?

  24 juillet 2014, par teslasimus

  I’m unable to merge two avi videos together.
  google is full of below examples :

  cat file1.avi file2.avi file3.avi > video_draft.avi
  
  after appending the data together using cat above, you need to re-index the draft movie like this:
  
  
  
  mencoder video_draft.avi -o video_final.avi -forceidx -ovc copy -oac copy
  
  Now you're video_final.avi file will be right to go.

  but it doesn’t work for me, the first video is converted and that’s it.

• Investigating Steam for Linux

  1er mars 2013, par Multimedia Mike — Game Hacking

  Valve recently released the final, public version of their Steam client for Linux, and the Linux world rejoiced. At least, it probably did. The announcement was 2 weeks ago on Valentine’s Day and I had other things on my mind, so I missed any fanfare. When framed in this manner, the announcement timing becomes suspect– it’s as though Linux enthusiasts would have plenty of time that day or something.

  
  
  

  Taming the Frontier
  Speculation about a Linux Steam client had been kicking around for nearly as long as Steam has existed. However, sometime last year, the rumors became more substantive.

  I naturally wondered how to port something like Steam to Linux. I have some experience with trying to make a necessarily binary-only program that runs on Linux. I’m fairly well-versed in the assorted technical challenges that one might face when attempting such a feat. Because of this, whenever I hear rumors that a company might be entertaining the notion of porting a major piece of proprietary software to Linux, my instinctive reflex is, “What ?! Why, you fools ?! Save yourselves !”

  At least, that’s how it used to be. The proposal of developing a proprietary binary for Linux has been rendered considerably less insane by a few developments, for example :

  1. The rise of Ubuntu Linux as a quasi de facto standard for desktop Linux computing
  2. The increasing homogeneity in personal desktop computing technology

  What I would like to know is how the Steam client runs on Linux. Does it rely on any libraries being present on the system ? Or does it bring its own ? The latter is a trick that proprietary programs can use– transport all of the shared libraries that the main program binary depends upon, install them someplace out of the way on the filesystem, probably in /opt, and then make the main program a shell script which sets a preload path to rely on the known quantity libraries instead of the copies already on the system.

  Downloading and Installing the Client
  For this exercise, I installed x86_64 desktop Ubuntu 12.04 Linux on a l33t gaming rig that was totally top of the line about 5 years ago, and that someone didn’t want anymore and handed down to me recently. So it should be ideal for this project.

  At first, I was blown away– the Linux client is in a .deb package that is less than 2 MB large. I unpacked the steam.deb file and found a bunch of support libraries — mostly X11 and standard C/C++ runtimes. Just as I suspected. Still, I can’t believe how small the thing is. However, my amazement quickly abated when I actually ran Steam and saw this :

  
  
  

  So it turns out steam.db is just the installer program which immediately proceeds to download an additional 160+ MB of data. So there’s actually a lot more information to possibly sift through.
  
  Another component of the installation is to basically run a big ‘apt-get install’ command to make sure a bunch of required packages are installed :

  
  
  

  After all these installation steps, the client was ready to run. However, whenever I tried to do so, I got this dialog which would cause Steam to close when the dialog was dismissed.

  
  
  

  Not a huge deal ; later NVIDIA drivers are fairly straightforward to install on Ubuntu Linux. After a few minutes of downloading, installing and restarting X, Steam ran with minimal complaint (it still had some issue regarding the video drivers but didn’t seem to consider it a deal-breaker).

  Using Steam on Linux

  So here’s Steam running on Linux :

  
  
  

  If you have experience with using Steam on Windows or Mac, you might observe that it looks exactly the same. I don’t have a very expansive library of games (I only started using Steam because purchasing a few computer components a few years ago entitled me to some free Steam downloads of some of the games on the list in the screenshot). I didn’t really expect any of the games to have Linux versions yet, but it turns out that the indie darling FTL : Faster Than Light has been ported to Linux. FTL was a much-heralded Kickstarter success story and sounded like something I wanted to support. I purchased this from Steam shortly after its release last year and was able to download the Linux version at no additional cost with a single click.

  It runs natively on Linux (note the Ubuntu desktop window decorations) :

  
  
  

  You might notice from the main Steam client that, despite purchasing FTL about a 1/2 year ago and starting it up at least a 1/2 dozen times, I haven’t really invested a whole lot of time into it. I only managed to get about 2 minutes further this time :

  
  
  

  What can I say ? This game just bores me to tears. It’s frustrating because I know that this is one of the cool games that all real gamers are supposed to like, but I practically catch myself nodding off every time I try to run through the tutorial. It’s strange to think that I’ve invested far more time into games that offer considerably less stimulation. That’s probably because I had far more free time compared to gaming options during those times.

  But that’s neither here nor there. We’ll file this under “games that aren’t for me.” I’m glad that people like FTL and a little indie underdog has met with such success. And I’m pleased that Steam on Linux works. It’s native and the games are also native, which is all quite laudable (there was speculation that everything would just be running on top of a Wine layer).

  Deeper Analysis
  So I set out wondering how Steam was able to create a proprietary program that would satisfy a large enough cross-section of Linux users (i.e., on different platforms and distros). Answer : well, they didn’t, per the stated requirements. The installation is only tuned to work on Ubuntu 12.04. However, it works on both 32- and 64-bit platforms, the only 2 desktop CPU platforms that matter these days (unless ARM somehow makes inroads on the desktop). The Steam client is quite clearly an x86_32 binary– look at the terminal screenshot above and observe that it’s downloading all :i386 support libraries.

  The file /usr/bin/steam isn’t a binary but a launcher shell script (something you’ll also see if you investigate /usr/bin/firefox on a Linux system). Here’s an interesting tidbit :

  function detect_platform()
  
    # Maybe be smarter someday
    # Right now this is the only platform we have a bootstrap for, so hard-code it.
    echo ubuntu12_32
  
  

  I wager that it’s possible to get Steam running on other distributions, it probably just takes a little more effort (assuming that Steam doesn’t put too much effort into thwarting such attempts).

  As for the FTL game, it comes with binaries and libraries for both x86_32 and x86_64. So, good work to the dev team for creating and testing both versions. FTL also distributes versions of the libraries it expects to work with.

  I suspect that the Steam client overall is largely a WWW rendering engine underneath the covers. That would help explain how Valve is able to achieve such a consistent look and feel, not only across OS platforms, but also through a web browser. When I browse the Steam store through Google Chrome, it looks and feels exactly like the native desktop client. When I first thought of how someone could port Steam to Linux, I immediately wondered about how they would do the UI.

  A little Googling for “steam uses webkit” (just a hunch) confirms my hypothesis.

• Deobfuscation Redux : JavaScript

  20 juin 2011, par Multimedia Mike — Reverse Engineering, deobfuscation, javascript, programming

  Google recently released version 12 of their Chrome browser. This version adds a new feature that automatically allows deobfuscating obfuscated JavaScript source code.

  Before :

  
  
  

  After :

  
  
  

  As a reverse engineering purist, I was a bit annoyed. Not at the feature, just the naming. This is clearly code beautification but not necessarily deobfuscation. The real obfuscation comes not from removing whitespace but from renaming variable and function names to terse 1- and 2-letter identifiers. True automated deobfuscation — which entails recovering the original variable and function identifiers as well as source code comments — is basically impossible.

  Still, it makes me wonder if there is any interest in a JavaScript deobfuscator that operates similar to my Java deobfuscator which was one of the first things I published on this blog. The general idea is automatically replace function names with random English verbs (since functions correspond to actions) and variable names with random animal names (I decided "English nouns" encompassed too broad a category of words). I suspect the day that someone releases a proprietary multimedia codec in a pure (though obfuscated) JavaScript format is that day that I will try to accomplish this, if it hasn’t been done already.

  See also :

  • Success on the Java De-obfuscation Front