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• Learn Multimedia Programming By Writing A JPEG Decoder

  6 janvier 2011, par Multimedia Mike — Programming

  For those of you who hack on multimedia tech, how did you get started ? Did you begin by studying the mathematical underpinnings of multimedia codec algorithms ? Or did you find a practical problem and jump right in by writing code ? (Personally, I was always more of a nuts & bolts hacker than a math guy.) I ask because I occasionally get emails from aspiring multimedia hackers who want to know where to begin. Invariably, they want to go the math-first route. I heavily discourage this approach.

  I have a crazy idea for anyone who wants a crash course on multimedia hacking : write a JPEG decoder. In doing so, you will be exposed to a lot of key domain concepts such as bitstream parsing, Huffman decoding, dequantization, zigzagging, the dreaded (inverse) discrete cosine transform, YUV vs. RGB colorspaces, macroblock organization, delta coding, and run length coding.

  Sure, JPEG decoding is a solved problem. But that’s hardly the point. Why would you enter an unfamiliar field and hope to come up to speed on the basics by leaping straight into the domain’s unsolved problems ? If you are successful in this exercise, no one will ever use the fruits of your labor, but that doesn’t really matter.

  So, do you want to learn multimedia hacking quickly ? Then grab a JPEG file (maybe create a few contrived ones that are small, have friendly dimensions, and feature predictable patterns), grab a good JPEG reference, and implement the decoding algorithm in the language and platform of your choice.

  On the matter of the reference, my personal favorite reference has always been A note about the JPEG decoding algorithm by Cristi Cuturicu. The English grammar is a bit dodgy but overall, it might be the best reference you’ll find on the matter— as simple as it needs to be, but no simpler.

  Good luck !

• Not able to generate video using ffmpeg

  27 janvier 2014, par user3239425

  I need to generate a vedio from a web page by capturing the screen. I tried in several ways but not able to find the solution. Any help can be appreciated. I am using phantomJS and FFmpeg

  Thanks
  Jaya

• Videoediting SDK C#

  10 avril 2013, par user2265112

  I'm currently working on a project were i have to collect a videostream from a videoserver. This is done by the videoservers SDK where i get a videoclip output.
  From this point i want to be able to cut at specific places in the videoclip or more specifically : trim out a specific part in the video.
  This will be done for three videoclips and then i want to combine these videos into one wide-screen split-screen videoclip. You should be able to see clip1,clip2,clip3 simultaneously in one frame.

  As of now i have a solution for this where i pass arguments to ffmpeg. This works but are relatively slow and i don't get errormessages if something goes wrong. Well, i use a streamreader to get some info.

  My question is : Is there a good well-documented library for C# i could use instead ? That ofcourse can provide the same functionality.
  I have looked at directshow but that didn't help me to much. And avisynth has the problem that it doesn't generate its own videoclip, if im not mistaken ?

  Kind Regards.