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• Rolling screen capture with ffmpeg on windows

  11 décembre 2020, par gap210

  I have the following code to capture a video stream from my webcam. I use ffmpeg to write to named windows pipe, then read it with python and display with opencv. The thing is that the opencv stream is 'rolling' as shown here https://www.youtube.com/watch?v=H78TRo3DZIo

  


  If I capture the output to a video instead of a pipe, with the command :

  


  ffmpeg -f dshow -video_size 1920x1080 -framerate 60 -i video="USB Video" -c:v copy out.avi

  


  everything looks fine. What should I change to achieve the desired effect ? (non-rolling stream)

  


  My code below :

  


  import cv2
import time
import subprocess
import numpy as np

w, h = 800, 600

# Get frame generator
gen = ffmpegGrab()

# Get start time
start = time.time()

# Read video frames from ffmpeg in loop
nFrames = 0
cmd = 'C:/Users/......./Downloads/ffmpeg-4.3.1-2020-11-19-full_build/bin/ffmpeg.exe -f dshow -framerate 60 -video_size 800x600 -i video="USB Video" -pix_fmt bgr24 -vcodec rawvideo -f image2pipe -'

proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, shell=True, bufsize=10**9)
while True:
    # Read next frame from ffmpeg

    frame = proc.stdout.read(w * h * 3)
    frame = np.frombuffer(frame, dtype=np.uint8).reshape((h, w, 3))
    cv2.imshow('screenshot', frame)

    if cv2.waitKey(1) == ord("q"):
        break

    fps = nFrames / (time.time() - start)
    print(f'FPS: {fps}')

cv2.destroyAllWindows()


  


• Live streaming video on multiple platforms [closed]

  4 mars 2019, par Nikolay Nikolov

  I want to build an application similar to Twitch/YouTube, which mainly offers two things (and a couple of other, but they are not related to the question) - to record and send live streams and to watch other people’s live streams. Basically, if I wanted to build Twitch, where would I start in terms of protocols and back-end libraries for the processing and sending/receiving of video segments (more detailed questions follow) ? I am new to the video streaming software development and need a bit of guidance on where/how to start.

  Here are the details/requirements :

  • Video and audio
  • Scalability and low latency are more important than supreme quality
  • Adaptive bit-rate
  • No services like Wowza and such (I am willing to build the whole structure)
  • Has to work on iOS and Android (Desktop support is not as important)
  • The users should be able to watch every stream and every user should be able to stream through his camera
  • VOD is not as important
  • Going back in the stream is not as important

  If I have it right, this is how the whole process should work :

  • Android/iOS camera records video
  • Simultaneously the app saves every x seconds as a single segment and sends it to the server
  • Server processes the video in different bit rates and saves them
  • Another user requests stream based on the bandwidth of its internet connection
  • Server responds with a playlist of segments and sends each new chunk of video to the user

  Questions :

  • What protocols should I be using (HLS, MPEG-DASH, WebRTC, RTSP, etc.) and do these protocols have implementations on Android/iOS or do I have to implement them myself ?
  • What books/other resources would you recommend ?

  Thank you very much for reading my question and I look forward to reading your answers !

• avformat/movenccenc : Fix memory leak for muxing CENC-encrypted files

  31 janvier 2021, par Vadym Bezdushnyi

  avformat/movenccenc : Fix memory leak for muxing CENC-encrypted files
  Memory for auxillary_info was not freed after usage.
  Leak can be reproduced with following commands :
  Optionally, generate input video :
  
  ffmpeg -f lavfi -i testsrc=duration=10:size=1280x720:rate=30 input.mp4
  Run ffmpeg with valgrind :
  
  valgrind —leak-check=full —show-leak-kinds=all \
  
  ffmpeg -y -i input.mp4 -vcodec copy -acodec copy \
  
   encryption_scheme cenc-aes-ctr \
  
   encryption_key 00000000000000000000000000000000 \
  
   encryption_kid 00000000000000000000000000000000 \
  
  ffmpeg_encrypted.mp4
  For test video which has duration of 10 sec, leak is 4 Kb.
  
  For 100 sec video, leak will be 33 Kb. Most likely,
  
  leaked memory will grow linearly to the number of input frames.
  Signed-off-by : Vadym Bezdushnyi <vadim.bezdush@gmail.com>
  
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavformat/movenccenc.c