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• Merge commit ’6509012398435252979e149ea4a73438d2107600’

  9 mars 2014, par Michael Niedermayer

  Merge commit ’6509012398435252979e149ea4a73438d2107600’
  * commit ’6509012398435252979e149ea4a73438d2107600’ :
  
    isom : add Radius DV YUV FourCCs
  See : a489db6cde48ed03c370a2f71b1be1e3485bc5db
  
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

• Using OpenCV 2.4.4 with FFmpeg in Windows

  22 décembre 2015, par aardvarkk

  I know there are other questions dealing with FFmpeg usage in OpenCV, but most of them appear to be outdated.

  By opening up the makefiles in CMake, I can verify that I’ve got the WITH_FFMPEG flag on. My output folder for the OpenCV build contains a bin folder, within which are Debug and Release folders, each containing a copy of a .dll file entitled opencv_ffmpeg244.dll. I can step into the source code of OpenCV when I create a VideoWriter and verify that the function pointers to the .dll get filled correctly. That much appears to be working.

  If I use the FOURCC code of CV_FOURCC_PROMPT, the following codecs work properly :

  • Microsoft Video 1
  • Intel IYUV codec
  • Logitech Video (I420)
  • Cinepak Codec by Radius
  • Full Frames (Uncompressed)

  The following codecs do not work properly (ie. produce a 0kb video file) :

  • Microsoft RLE

  If my understanding is correct, using FFMPEG should allow for encoding video using a whole bunch of new codecs (x264, DIVX, XVID, and so on). However, none of these appear in the prompt. Manually setting them by their FOURCC codes using the macro CV_FOURCC(...) also doesn’t work. For instance, using this : CV_FOURCC('X','2','6','4') produces the message :

  Could not find encoder for codec id 28: Encoder not found

  and makes a video file of size 0kb.

  Using this : CV_FOURCC('X','V','I','D') produces no error message, and makes a video file of 6kb that will not play in Windows Media Player or VLC.

  I tried manually downloaded the Xvid codec from Xvid.org. Once that was installed, it appeared under the VFW selection in the prompt, and the encoding worked properly. So it’s close to a solution, but if I try to set the FOURCC code directly, it still fails as above ! I have to pick it from the prompt every time. Isn’t FFmpeg supposed to include a whole bunch of codecs ? If so, why am I manually downloading the codec instead of using the one built into FFmpeg ?

  What am I missing here ? Is there a way to check that FFMPEG is "enabled" ? It seems like the only codecs available in the prompt are VFW codecs, not the FFMPEG ones. The .dll has been built and is sitting in the same folder as the executable, but it appears it’s not being used in any way.

  Lots of related questions here. Hoping to find somebody knowledgeable about the FFmpeg implementation in OpenCV and with some knowledge of how all of these pieces fit together.

• The Fastest Way To Learn Assembly Language

  4 septembre 2011, par Multimedia Mike — Programming

  I saw an old StackOverflow thread linked from Hacker News asking how to whether it’s worthwhile to learn assembly language and how to go about doing so. I’d like to take a stab at the last question.

  The fastest way to learn an assembly language is to reverse engineer something. Seriously, start with something that you know (like a C program that you wrote yourself) and take it apart. The good news is that assembly language is very simple and you will get a lot of practice in a short amount of time with RE.

  So here’s how you do it :

  • Take a simple program in C and build it with your tool chain, whether GNU gcc on Linux, Xcode on Mac, or MSVC on Windows. Also, make sure to turn on debugging symbols during compilation (this will help annotate the disassembly).
  • On Linux, use objdump : objdump -d program_binary
  • On Mac, use otool : otool -tV program_binary
  • On Windows : I admit, I’m a bit fuzzy on this one– I’m quite certain there’s a standard MSVC tool that prints the assembly listing.

  Anyway, look at the disassembled code and find the main() function. Work from there. Whatever the first instruction is, look it up on Google. You’ll likely find various CPU manuals that will explain the simple operation of the instruction. Look up the next unfamiliar instruction, then the next. Trust me, you’ll become an ASM expert in no time.

  Good luck !