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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()

• Gstreamer preserve timestamp when encoding ts segments

  1er juillet 2021, par Guru Govindan

  I have a series of ts files(h265) which are part of a m3u8 manifest which are fed into the pipeline through fdsrc. I use the following pipeline to transcode them to H264 to be played on a Hlsjs web browser.

  


  cat 2021-06-30T00-55-41Z_2000000.ts | gst-launch-1.0  -q mpegtsmux name=mux ! fdsink fd=1 fdsrc ! tsdemux name=demux demux. ! queue ! h265parse ! nvh265dec ! videoconvert ! videoscale ! video/x-raw,width=640,height=360 ! nvh264enc ! mux.


  


  The individual ts segments are transcoded successfully and can be played.

  


  However the DTS is out of aligment and when these ts segments are played as part of the hls manifest, it is not able to play as DTS is out of order.

  


  [mpegts @ 0x7fb69100a400] DTS 6496420096 < 6496446847 out of order
[hls @ 0x7fb69580ea00] DTS 6496420096 < 6496446847 out of order


  


  In FFMPEG we have copyts to preserve the timestamp.
Is there something similar in gstreamer to preserve the timestamp ? Or atleast generate a timestamp with the current time so that the player doesnt complain ?

  


  I tried fdsrc do-timestamp=true but that didnt work.

  


  I appreciate any help in this.

  


  Best

  


• Can´t convert .mp4 file to .mjpeg file with ffmpeg

  19 février 2018, par Herr HupfDohle

  I use ffmpeg to convert a .mp4 file to a .mjpeg file and I fail doing so.
  What i tried so far :
  Converting directly from .mp4 to .mjpeg with one of these :

      "ffmpeg -i input.mp4 output.mjpeg"
  
      "ffmpeg -i input.mp4 -framerate 25 output.mjpeg"

  Getting all the individual images of my video (which worked fine) and put them together to a .mjpeg file did not work as well.

      "ffmpeg -i input.mp4 image%d.jpeg"
  
      "ffmpeg -f image2 -i image%d.jpeg output.mjpeg", or
  
      "ffmpeg -f image2 -i image%d.jpeg -framerate 25 output.mjpeg"

  "Solutions" like the following one did not work, cause I need a file extension .mjpeg so -c:v mjpeg is not enough cause I end up with sth. like .mov !

  "ffmpeg -i input.mov -c:v mjpeg -q:v 3 -huffman optimal -an output.mov"

  To view my files I use vlc player.

  I always end up with a .mjpeg file which has the length of 10 seconds and only shows the very first image of my 4000 pictures.