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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 ! ^^

• SharedArrayBuffer not defined when using Cypress

  15 janvier 2023, par unloco

  I'm using Vite and Cypress for dev and testing

  


  I'm loading ffmpeg, it loads fine on Chrome but on Cypress, it gives this error

  


  ReferenceError: SharedArrayBuffer is not defined


  


  Apparently, it's caused by cross origin isolation.

  


  I tried disabling web security in Cypress.json but it didn't help

  


  Sample code

  


  import { createFFmpeg } from "@ffmpeg/ffmpeg"

const ffmpeg = createFFmpeg({ log: true })
ffmpeg.load()



  


  Is there a workaround ?

  


  Minimal Repro
https://github.com/unlocomqx/cypress-ffmpeg

  


• retransmit incoming vp8-rtp-udp stream as the same rtp

  9 janvier 2014, par rub

  S'cuse the title.. I find it hard even to write up the question :

  I am trying to use ffmpeg to channel an incoming realtime video stream (Android VoIP call) into a local-network PC. I have compiled FFMPEG to android using the most recent NDK/FFMPEG git sources, but I find it hard to get all the configuration right.

  Now, I understand that FFMPEG has retransmission functionality - I found a number of command line examples, similar to what I need :

  **ffmpeg -re -i udp://1.2.3.4:1234  http://127.0.0.1:8090/feed1.ffm**

  What I don't understand :

  1. Which process to use : ffmpeg / ffserver / ffplay ??
  2. Do I have to use a ffserver.conf file (IP security right ?)
  3. Can I use sdp for incoming udp channel (I have the SDP from the VoIP/SIP call)

  Thanks