Recherche avancée

Sur d’autres sites (9936)

• Revision 79afb5eb41 : Use lrand48 on Android When building x86 assembly use lrand48 instead of the un

  13 juin 2014, par Johann

  Changed Paths :
   Modify /vp8/common/x86/postproc_mmx.asm

  
   Modify /vp8/common/x86/postproc_sse2.asm

  
   Delete /vp8/common/x86/postproc_x86.c

  
   Modify /vp8/vp8_common.mk

  
   Modify /vp9/common/x86/vp9_postproc_mmx.asm

  
   Modify /vp9/common/x86/vp9_postproc_sse2.asm

  
   Modify /vpx_ports/x86_abi_support.asm

  
  
  Use lrand48 on Android

  When building x86 assembly use lrand48 instead of the
  undocumented inlined _rand function.

  Android now supports rand()
  https://android-review.googlesource.com/97731
  but only for new versions. Original workaround :
  https://gerrit.chromium.org/gerrit/15744

  Change-Id : I130566837d5bfc9e54187ebe9807350d1a7dab2a

• How to decide raw h264 using pyav ?

  26 septembre 2016, par Winston Chen

  I am playing pylive555 (Please refer to this article.) against my web cams. I am able to get the bytes of each frame (be it i frame, p frame, or b frame) out using the code listed in the article.

  However, what comes next will be to decode the bytes into an actual frame image or numpy array (just i frame, p frame, or b frame themselves, not applying delta onto the i frames when it comes to p frame or b frame).

  I did some research online and found that a we might be able to use avcodec_decode_video2 function like it’s said in this post. Has anybody done this with pyAv ? Do you mind sharing how you did it ?

• Having trouble obtaining the time from RTP Timestamps obtained through OpenCV

  24 août 2019, par Fr0sty

  I am finding it a bit difficult trying to understand whether or not the hack around with FFmpeg and OpenCV really provided a RTP timestamp. My last post helped a little bit but got me stuck in trying to validate the timestamps obtained through this work around by modifying ffmpeg and opencv.

  FFmpeg version : 4.1.0
  OpenCV version : 3.4.1

  import cv2
  
  import time
  
  from datetime import datetime, date
  
  
  
  uri = 'rtsp://admin:password@192.168.1.66:554/Streaming/Channels/101'
  
  cap = cv2.VideoCapture(uri)
  
  '''One is the offset between the two epochs. Unix uses an epoch located at 1/1/1970-00:00h (UTC) and NTP uses 1/1/1900-00:00h.
  
  This leads to an offset equivalent to 70 years in seconds (there are 17 leap years between the two dates so the offset is'''
  
  time_offset = 2208988800 # (70*365 + 17)*86400 = 2208988800 (in seconds)
  
  # offset = 3775484294
  
  days = 43697
  
  pdat = "1900-01-01 00:00:00:00"
  
  mdat = "2019-08-23 22:02:44:00" # str(datetime.now()) + str(datetime.now().time())
  
  pdate = datetime.strptime(pdat, "%Y-%m-%d %H:%M:%S:%f").date()
  
  mdate = datetime.strptime(mdat, "%Y-%m-%d %H:%M:%S:%f").date()
  
  delta = (mdate - pdate).days
  
  offset = delta * 86400
  
  def time_delta(s):
  
      return (s - time_offset)
  
  
  
  while True:
  
      frame_exists, curr_frame = cap.read()
  
      if frame_exists:
  
          seconds = cap.getRTPTimeStampSeconds()
  
          fraction = cap.getRTPTimeStampFraction()
  
          timestamp = cap.getRTPTimeStampTs()
  
          unix_offset = seconds - time_offset
  
          msec = int((int(fraction) / 0xFFFFFFFF) * 1000.0)
  
          ts = float(str(unix_offset) + "." + str(msec))
  
          # print("Timestamp per Frame:%i" % timestamp)
  
          print((datetime.fromtimestamp(float(ts) + offset)))
  
  cap.release()

  My Output :

  On August 23, 2019 at 22:02

  ...
  
  2019-08-23 13:59:52.781000
  
  2019-08-23 13:59:52.726000
  
  2019-08-23 13:59:52.671000
  
  2019-08-23 13:59:52.616000
  
  2019-08-23 13:59:52.561000
  
  2019-08-23 13:59:52.506000
  
  2019-08-23 13:59:52.451000
  
  2019-08-23 13:59:52.396000
  
  2019-08-23 13:59:52.342000
  
  2019-08-23 13:59:52.287000
  
  2019-08-23 13:59:52.232000
  
  2019-08-23 13:59:52.177000
  
  2019-08-23 13:59:52.122000
  
  2019-08-23 13:59:52.067000
  
  2019-08-23 13:59:52.012000
  
  2019-08-23 13:59:53.570000
  
  2019-08-23 13:59:53.020000
  
  2019-08-23 13:59:53.847000
  
  2019-08-23 13:59:53.792000

  I’ve noticed how the time increments weirdly (that’s not suppose to happen in the real, current time), such as the last two lines and a few others in between in the output. A bit flabbergasted as to what went wrong. Also trying this out on multiple IP cameras, with each showing a different timestamp probably related to when they were turned on.