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• 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 ! ^^

• How do I make FFMPEG use localized strftime with drawtext ?

  3 décembre 2022, par Randy Michnovicz

  I'm trying to write a script to use FFMPEG to draw localized timestamps on a video, but I'm not having much luck.

  


  I can confirm I have the locale fr_FR.UTF-8 installed on my system by running the following command : LC_ALL=fr_FR.UTF-8 date

  


  However, the following command produces a 4 second video beginning with the string "Monday 28 November 2022 19:00:47 PST" on both my Mac and an Alpine Linux docker container :

  


  LC_ALL=fr_FR.UTF-8 ffmpeg -hide_banner -f lavfi -i color=size=1024x768:rate=25:color=black -c:v libx264 -c:a aac -filter_complex drawtext=expansion=normal:fontsize=18:fontcolor=white:box=1:boxcolor=black@0.5:text='%{pts\\:localtime\\:1669690847\\:%A %-d %B %Y %X %Z}' -t 4 -y out.mp4

  


  Does anyone know how to make it create strings with non-English text ?

  


• creating video from selected images using FFMPEG through command Line Android

  7 septembre 2016, par Raheel Mushtaq

  i am trying to make a video from selected images from command line using ffmpeg in android

  using this project as my source i m trying to make video

  this is the command i m trying to create video

     String[] ffmpegCommand = {ffmpegBin,
  
              "-y",
  
              "-qscale",
  
              "1",
  
              "-r", "" + frameRate,
  
              "-i", image1.getAbsolutePath(),
  
              "-t", "" + (((4) * 30) + 4), //"-s",heightwidth,
  
              "-i", image2.getAbsolutePath(),
  
              "-t", "" + (((4) * 30) + 4), //"-s",heightwidth,
  
              "-i", image3.getAbsolutePath(),
  
              "-t", "" + (((4) * 30) + 4), //"-s",heightwidth,
  
              "-i", image4.getAbsolutePath(),
  
              "-t", "" + (((4) * 30) + 4), //"-s",heightwidth,
  
              "-vcodec",
  
              "libx264",
  
              "-s",
  
              "640x480",
  
              outputFile.getAbsolutePath()};

  but the video created shows only 1st image and video is created of less than a second

  what is the problem in this statement ? and why only 1 image is shown in video ?

  sorry about my bad english