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• Can OpenCV decode H264 - MPEG-4 AVC (part 10)

  15 avril 2015, par Sergiy

  I am trying to use OpenCV (python bindings) to connect to a UDP multicast and recover individual received frames for post-processing.

  I can connect to my multicast via VLC, and VLC displays the broadcast with no issues at all. VLC reports that the codec it uses for decoding is H264 - MPEG-4 AVC (part 10).

  When I try to decode using OpenCV, I do see my video stream, but many frames appear fragmented. The frames appear as if the last line of pixels just got repeated to fill in the rest of the image (sometimes 75% or more of the whole image). OpenCV reports decoding errors (error while decoding MB ...., bytestream ).

  Is there any way to force OpenCV to use whatever codec VLC is using ? I tried to specify the specific codec to use in my code for OpenCV but it seems to have no effect.

  The code I am using is below :

  import numpy as np
  
  import cv2
  
  from cv2 import cv
  
  
  
  cap = cv2.VideoCapture()
  
  cap.set(cv.CV_CAP_PROP_FOURCC, cv.CV_FOURCC('A','V','C','1')) 
  
  cwi=cap.open(r'myurlandport')
  
  
  
  counter = 0
  
  
  
  while(cap.isOpened()):
  
  
  
      ret, frame = cap.read()
  
  
  
  
  
      counter += 1
  
  
  
      if counter % 30 == 0:
  
          cv2.imshow('frame', frame)
  
          if cv2.waitKey(1) & 0xFF == ord('q'):
  
              break
  
  
  
  cap.release()
  
  cv2.destroyAllWindows()

• Revision 1ed0e1beb5 : Move SVC per-frame loop from sample app into libvpx proper SVC multiple layer p

  23 octobre 2013, par Ivan Maltz

  Changed Paths :
   Modify /examples.mk

  
   Modify /libs.mk

  
   Add /test/svc_test.cc

  
   Modify /test/test.mk

  
   Modify /vp9/common/vp9_onyx.h

  
   Modify /vp9/encoder/vp9_onyx_if.c

  
   Modify /vp9/vp9_cx_iface.c

  
   Modify /vp9_spatial_scalable_encoder.c

  
   Modify /vpx/exports_enc

  
   Add /vpx/src/svc_encodeframe.c

  
   Add /vpx/svc_context.h

  
   Modify /vpx/vp8cx.h

  
   Modify /vpx/vpx_codec.mk

  
  
  Move SVC per-frame loop from sample app into libvpx proper

  SVC multiple layer per frame encoding is invoked with vpx_svc_init and
  vpx_svc_encode. These interfaces are designed to be invoked from ffmpeg.
  Additional improvements :
   make dummy frame handling a bit more explicit
   fixed bug with single layer encodes
   track individual frame sizes and psnrs instead of averages
   parameterized quantizer, 16th scalefactors, more logging,
   enabled single layer encodes to generate baseline
   include new mode for 3 layer I frame with 5 total layers

  Change-Id : I46cfa600d102e208c6af8acd6132e0cc25cda8d4

• Merging 2 videos with overlay causes async problems

  3 novembre 2014, par Gnagy

  I’m using following FFMPEG command to merge 2 MKV inputs with the overlay parameter.
  The result should be one output with input1 on top of input2.
  In the process, the output should be webm.
  Both inputs are of the same length (with a margin of a second).

  ffmpeg -i input1.mkv -i input2.mkv -y -filter_complex [0:v]select=1, setpts=PTS-STARTPTS, scale=400:300, pad=400:600 [top]; [1:v]select=1, setpts=PTS-STARTPTS, scale=400:300 [bottom]; [top][bottom] overlay=0:300 [out]; [0:a:0][1:a:0] amerge=inputs=2 [a]; [a] asetpts=PTS-STARTPTS [a] -map [a] -c:v libvpx -crf 10 -b:v 360K -q:v 7 -c:a libvorbis -b:a 32k -map [out] output.webm

  This command does what it’s supposed to do.

  However, the 2 videos are not totally in sync.

  The input1 on the top plays decently while the input2 on the bottom has black frames, slows down or speeds up and causes the audio and video to be out of sync.

  To rule out the individual quality of the inputs, we switched the position of the videos and the top video always plays decently.

  How can we fix this ?