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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 commit ’0508faaa11bf7507ffdd655aee57c9dc5a8203f4’

  29 mai 2015, par Michael Niedermayer

  Merge commit ’0508faaa11bf7507ffdd655aee57c9dc5a8203f4’
  * commit ’0508faaa11bf7507ffdd655aee57c9dc5a8203f4’ :
  
    rtmpdh : Pass the actual buffer size of the output secret key
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavformat/rtmpcrypt.c
  • [DH] libavformat/rtmpdh.c
  • [DH] libavformat/rtmpdh.h

• How can I pass chapter data to multiple streams with tee muxer

  11 février 2021, par jonnywishbone

  I'm trying to transcode several videos from their original format into 4K and 1080p HD MKV and/or MP4 containers. The original contains chapter info, but no matter how many incarnations of ffmpeg flags/settings I've tried, the chapter data doesn't wind up in either output stream.

  


  Here's a redacted version of the command I'm using (PowerShell 7.1) :
...

  


     ffmpeg -i "XXXXXxxxx.mkv" `
   -loglevel repeat+warning -stats  -hide_banner -y -benchmark `
   -flags +global_header -filter_complex `
   "[0:v]split=2[s0][s1]; `
   [s0]null[v2160]; [s1]scale=1920:-1[v1080]" `
   -to 00:01:05 -map "[v2160]" -map "[v1080]"  -map 0:1 -map_metadata 0 -map_chapters 0 -movflags use_metadata_tags `
   -c:v libx265  -x265-params  `
   "log-level=error" -pix_fmt yuv420p10le   `
  -b:v:0 3100K -b:v:1 2200K -minrate 400K -bufsize 8M  `
   -c:a:0 aac  -ac:a:0 2   -ar:a:0 48000 -af:a:0 dynaudnorm  -b:a:0 192k -disposition:a:0 default+original `
   -metadata:s:a:0 language=eng -metadata:s:a:0 title="aac-stereo" -metadata:s:a:0 handler="aac-stereo" `
   -metadata comment=" "  -metadata title=""XXXXXxxxx"  `
   -f tee "[select=\'v:0,a\':f=matroska]`""XXXXXxxxx [2160p].mkv`"|[select=\'v:1,a\':f=matroska]`""XXXXXxxxx [1080p].mkv`""


  


  ...

  


  What's the secret sauce for getting chapter info passed to the output streams ? Is it a tee select of some sort ? A different -map_metadata -type setting ?

  


  Please forgive the odd code formatting - the editor really didn't know what to do with PowerShell back-tick escape characters that delimit quotes and other literals in PS scripting !