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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 ! ^^

• Merge pull request #3419 from matthewrhoden1/master

  24 février 2016, par blueimp

  Merge pull request #3419 from matthewrhoden1/master
  Wiki Update
  

• send point to point video stream using ffmpeg with rtsp (c++)

  8 décembre 2015, par seleciii44

  I need to send a h264 encoded video stream to a(only one) specific IP address with RTSP protocol on a windows PC with C++. I’m trying to use the FFMPEG library.

  I used the example in this post and i can play the stream as :

  ffplay -rtsp_flags listen -i rtsp://127.0.0.1:8554/live.sdp

  The problem is, according to the solution of post i need a server. Where -rtsp_flags listen option of ffplay behaves like a server.

  On the other hand, according to StreamingGuide of ffmpeg i can send a point to point stream like :

  ffmpeg -i INPUT -acodec libmp3lame -ar 11025 --f rtp rtp://host:port

  This is fine and works well. But i need to use rtsp. According to StreamingGuide again,

  Another option is to use RTP (which by default uses UDP) but by
  specifying it use TCP :

  ffmpeg -i input -f rtsp -rtsp_transport tcp rtsp://localhost:8888/live.sdp

  which seems to be what i’m looking for. Yet the ffmpeg tool seems to be doing nothing when i try this method (don’t know why i need tcp,but udp does not work neither). Why is that ?

  FFMPEG protocols documentation, says that i need to use a media server to send the video.

  • Why would i need a media server to just send the video stream to another PC or whatever ?
  • If i need a media server, how does the IP Camera sends the stream ?
  • If i have no option but to use a media server, could some one please recommend a server for Windows 7 ?
    • ffserver is only for linux
    • live555mediaServer seems to be used for local files or am i wrong ?
    • ..?

  Best regards,
  Gokhan.