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• Naive Sorenson Video 1 Encoder

  12 septembre 2010, par Multimedia Mike — General

  (Yes, the word is “naive” — or rather, “naïve” — not “native”. People always try to correct me when I use the word. Indeed, it should actually be written with 2 dots over the ‘i’ but who has a keyboard that can easily do that ?)

  At the most primitive level, programming a video encoder is about writing out a sequence of bits that the corresponding video decoder will understand. It’s sort of like creating a program — represented as a stream of opcodes — that will run on a given microprocessor or virtual machine. In fact, reading a video codec bitstream specification will reveal a lot of terminology along the lines of “transmitting information to the decoder” or “signaling the decoder to do xyz.”

  Creating a good encoder that will deliver decent quality at a reasonable bitrate is difficult. Creating a naive encoder that produces a technically compliant bitstream, not so much.

  
  
  

  When I wrote an FFmpeg encoder for Sorenson Video 1 (SVQ1), the first step was to just create a minimally compliant bitstream. The coarsest encoding mode that SVQ1 allows is to encode the average (mean) of each 16×16 block of samples. So I created an encoder that just encoded the mean of each block. Apple’s QuickTime Player was able to play the resulting video in all of its blocky glory. The result rather reminds me of the Super Nintendo’s mosaic effect.

  Level 5 blocks (mean-only 16×16 encoding) :
  

  
  
  

  Level 3 blocks (mean-only 8×8 encoding) :
  

  
  
  

  It’s one thing for your own decoder (in this case, FFmpeg’s own decoder) to be able to decode the data. The big test is whether the official decoder (in this case, Apple QuickTime Player) can decode the file.

  
  
  

  Now that’s a good feeling. After establishing that sort of baseline, it’s possible to adapt more and more features of the codec.

• Start/Stop Ffmpeg video capture

  2 novembre 2011, par Dasas

  I'm currently using ffmpeg for recording video from a webcam source.

  At the moment i use java to call for ffmpeg to execute.

  The code is pretty straightforward

  ffmpeg -f dshow -i video="Dualpix HD720p for Notebooks" -s cif -r 20 -f flv TEST.FLV
  
  Runtime.getRuntime().exec("rundll32 SHELL32.DLL,ShellExec_RunDLL " + cmd);

  and it works fine.

  The only real issue occour when when i need to stop the recording process.

  I know that i can press q or even ctrl+c in the CMD but i need to stop the process without keyboard input.

  That would be pretty easy to achive by killing the process but in this case ffmpeg do not finalize the video leaving me with a corrupt, need to fix, output.

  Is there any way to trigger the finalizing process "remotely".

  Thx,
  D.

  *******EDIT**********

  Thx for the prompt answer, i think you're referring to

  Process.getOutputStream()

  As for this case i have tried with this code :

  public Process doCommand(String cmd) throws Exception {
  
  
  
      rt = Runtime.getRuntime();
  
      Process proc = rt.exec(cmd);
  
      recOS= proc.getOutputStream();
  
      regcIS= proc.getInputStream();
  
  
  
      return proc;
  
  
  
  }
  
  
  
     receOS.write(("q/n".getBytes()));
  
     recOS.flush();

  I'm still getting an error, to be more specific, java.io.ioexception The pipe is being closed ...

• Efficient video compression for screen sharing ?

  15 juin 2014, par Maciej Jankowski

  I need to know what would be the most favorable approach for streaming screen content and controlling remote computer (mouse, keyboard). (I would like to build something like "one-click teamviewer")

  So my main question is about picking the video compression method for such requirements :

  1. Most information between subsequent frames stays the same
  2. Color depth can be degraded, but the details (text) must remain sharp
  3. It should work on low-end bandwidths : 512k and below
  4. Frames can be dropped