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• How to add arbitrary or custom metadata in MP4 ?

  13 avril 2021, par 大大大大萝卜凉

  The MP4 muxer in ffmpeg only allows certain metadata by default. I would like to add :

  


  com.android.model: Mi 10 Pro
xyz: +22.9835+113.3621/
com.android.version: 1
com.android.manufacturer: Xiaomi


  


  How can I add this with ffmpeg ?

  


• How would I assign multiple MMAP's from single file descriptor ?

  9 juin 2011, par Alex Stevens

  So, for my final year project, I'm using Video4Linux2 to pull YUV420 images from a camera, parse them through to x264 (which uses these images natively), and then send the encoded stream via Live555 to an RTP/RTCP compliant video player on a client over a wireless network. All of this I'm trying to do in real-time, so there'll be a control algorithm, but that's not the scope of this question. All of this - except Live555 - is being written in C. Currently, I'm near the end of encoding the video, but want to improve performance.

  To say the least, I've hit a snag... I'm trying to avoid User Space Pointers for V4L2 and use mmap(). I'm encoding video, but since it's YUV420, I've been malloc'ing new memory to hold the Y', U and V planes in three different variables for x264 to read upon. I would like to keep these variables as pointers to an mmap'ed piece of memory.

  However, the V4L2 device has one single file descriptor for the buffered stream, and I need to split the stream into three mmap'ed variables adhering to the YUV420 standard, like so...

  buffers[n_buffers].y_plane = mmap(NULL, (2 * width * height) / 3,
  
                                      PROT_READ | PROT_WRITE, MAP_SHARED,
  
                                      fd, buf.m.offset);
  
  buffers[n_buffers].u_plane = mmap(NULL, width * height / 6,
  
                                      PROT_READ | PROT_WRITE, MAP_SHARED,
  
                                      fd, buf.m.offset +
  
                                      ((2 * width * height) / 3 + 1) /
  
                                      sysconf(_SC_PAGE_SIZE));
  
  buffers[n_buffers].v_plane = mmap(NULL, width * height / 6,
  
                                      PROT_READ | PROT_WRITE, MAP_SHARED,
  
                                      fd, buf.m.offset +
  
                                      ((2 * width * height) / 3 + 
  
                                      width * height / 6 + 1) / 
  
                                      sysconf(_SC_PAGE_SIZE));

  Where "width" and "height" is the resolution of the video (eg. 640x480).

  From what I understand... MMAP seeks through a file, kind of like this (pseudoish-code) :

  fd = v4l2_open(...);
  
  lseek(fd, buf.m.offset + (2 * width * height) / 3);
  
  read(fd, buffers[n_buffers].u_plane, width * height / 6);

  My code is located in a Launchpad Repo here (for more background) :
  http://bazaar.launchpad.net/ alex-stevens/+junk/spyPanda/files (Revision 11)

  And the YUV420 format can be seen clearly from this Wiki illustration : http://en.wikipedia.org/wiki/File:Yuv420.svg (I essentially want to split up the Y, U, and V bytes into each mmap'ed memory)

  Anyone care to explain a way to mmap three variables to memory from the one file descriptor, or why I went wrong ? Or even hint at a better idea to parse the YUV420 buffer to x264 ? :P

  Cheers ! ^^

• Can't link FFmpeg in Visual Studio 2013

  22 février 2016, par Sir DrinksCoffeeALot

  I’m struggling with this for past 3-4 days with barely any progress. I’ve downloaded "dev" and "shared" archives and extracted them. "Dev" archive has .lib and .h files and "Shared" has .dll files needed for running app. These are the steps that i’ve done linking-wise :

  Project -> Properties -> Configuration Properties -> VC++ Directories -> Include Directories -> ...\ dev\ include

  Project -> Properties -> Configuration Properties -> VC++ Directories -> Library Directories -> ...\ dev\ lib

  Project -> Properties -> Configuration Properties -> C/C++ -> General -> Additional Include Directories -> ...\ dev\ include

  Project -> Properties -> Configuration Properties -> Linker -> General -> Additional Library Directories -> ...\ dev\ lib

  Project -> Properties -> Configuration Properties -> Linker -> Input -> Additional Dependencies -> avcodec.lib ... swscale.lib

  And when i try to build it i get following error :

  Error 1 error LNK2019: unresolved external symbol _avcodec_register_all referenced in function _main...

  I have no idea why,somehow .lib are not getting linked or something or i’ve done something wrong. It’s getting really frustrating and ffmpeg is crucial in project that i’m working on, basicly i can’t do anything without it. So please if someone could point me in right direction i would aprreciate it very much.

  This is the example that im trying to build.

  #include 
  
  extern "C"
  
  {
  
  
  
  #include "libavcodec\avcodec.h"
  
  }
  
  
  
  
  
  #pragma comment(lib, "avcodec.lib")
  
  
  
  int main()
  
  {
  
      printf("Trying avcodec_register_all... ");
  
      avcodec_register_all();
  
      printf("Done.\n");
  
      return 0;
  
  }

  Thank you in advance.