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• ffmpeg video stream output multiply when I modify viedo in OpenCV

  30 mars 2017, par trojek

  I try to implement a proof of concept program which : (1)get video from webcam, (2)do some operations on it, (3)stream modified video on a web page.

  I do it as follows :

  1) In open CV : open webcam stream and output frames as a rawvideo, capture.py looks :

    import cv2
  
    import sys
  
  
  
    cap = cv2.VideoCapture(0)
  
    while(cap.isOpened()):
  
      ret, frame = cap.read()
  
      if(ret):
  
        sys.stdout.write(frame.tostring())
  
      else:
  
        break

  2) Run ffmpeg server by execute : python2 capture.py | ffmpeg -framerate 30 -f rawvideo -pixel_format bgr24 -video_size 640x480 -i - -f mpegts -codec:v mpeg1video -s 640x480 -b:v 2500k -bf 0 http://localhost:8081/supersecret

  3) Run Websocket relay and http-server according to the instruction on page : https://github.com/phoboslab/jsmpeg, in order to stream video in a browser.

  I get the stream in browser, but when I apply any change(e.g. frame = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)) on the frame inside capture.py file I get 9 small stream instead of one.

  The same situation occurs when I change video resolution while starting ffmpeg server. When I stream directly from /dev/video0 insted of pipe I get the proper stream.

  How can I do some operations on the video and get the single image stream ?

• Live Streaming WebM with Wowza Server

  2 décembre 2010, par noreply@blogger.com (John Luther)

  Guest blogger Charlie Good is CTO and co-founder of Wowza Media Systems

  As a company, we at Wowza move fast and like to tinker. When WebM was announced in May, we saw it as a promising new approach to HTML5 video and decided to do an experiment with live WebM streaming over http.

  Adding WebM VP8 video and Vorbis audio to the other encoding formats that our server supported was easy (we designed the Wowza server to be codec-agnostic). We then created a WebMfile and implemented WebM HTTP streaming.

  We originally created the demo as a proof-of-concept for the IBC show in September, 2010 but have made it available to watch on our web site.

  The file is streamed live (more precisely, "pseudo-live") over http using the Wowza server-side publishing API (PDF). The result is very impressive ; playback starts fast and the VP8 image quality is fantastic.

  You will need a WebM-enabled browser or VLC media player 1.1.5 to view the live stream.

  If you’re interested in keeping up with Wowza’s WebM progress, visit Wowza Labs or drop us a note at info@wowzamedia.com.

  

• Color spot in FFmpeg output

  2 juin 2022, par Fabian Garcia

  I work in a company that serves multimedia content to different clients and one of these requests that the videos contain the following specifications :

  


  

  • Codec : H264 High@4.0

  


  • Mode : CBR 1 pass

  


  • Window Buffer : 5 secs

  


  • Frame Rate : 29.97/23.97

  


  • Key Frame Interval : 2 secs

  


  • Bitrate : 4000 Kbps

  


  • Size : 1920x1080

  


  • Window Buffer : 5 secs

  


  • GOP : closed

  


  • GOP size : fixed (no scene change detection)

  


  • Window Buffer : 5 secs

  


  • B Frames : As needed

  


  


  For the above, i build following script :

  


  ffmpeg -hide_banner -nostats -loglevel error -y
-init_hw_device cuda=cuda -hwaccel cuda -hwaccel_device cuda
-i 'video_source.mxf' -filter_hw_device cuda
-filter_complex '[0:v]format=nv12,hwupload,yadif_cuda,scale_cuda=1920:1080[v0]'
-map '[v0]' -c:v h264_nvenc -rc cbr -b:v 4M -bufsize 8M -x264-params "keyint=60:min-keyint=48:no-scenecut" -r '30000/1001' -profile:v high -level:v 4
-map 0:1 -c:a libfdk_aac -b:a 96k -ar 44100 -ac 2 -sample_fmt s16
'output.mp4'


  


  The inconvenience is that the generated output presents some color spots in the scene changes (it's a fade) as can be seen in the attached image.

  


  I could notice that in the output video, the time does not match the input precisely, the output is a few milliseconds ahead, I think that the color spot corresponds to the image that should be shown at that moment in the original video.

  


  Can you see something wrong in script ? Or maybe some concept that i don't know is causing a conflict with the output (This is my first time using ffmpeg).

  


  Thank for your help !