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• Variable fps (frame per second) in cv2

  17 octobre 2022, par Sepide

  I use cv2 for creating videos from different frames that I have. When I create the video, I cannot change the fps (frame per second). I want the video be slow at the beginning but fast towards the end, meaning small fps at the beginning but large ones towards the end. However, when I instantiate cv2.VideoWriter I cannot change the fps anymore. What should I do ?

  


  Replicable code

  


  import numpy as np
import cv2, os
import matplotlib

image_size = 200
def create_image_array(image_size):
  image_array = np.random.randn(image_size, image_size)
  row = np.random.randint(0, image_size)
  image_array[row, :] = 100
  return image_array

frame_numbers = 200
for i in range(frame_numbers):
  image_array = create_image_array(image_size)
  matplotlib.image.imsave(f'./shots/frame_{i:03d}.png', image_array)

def make_a_video(shots_folder, video_path):

    shots_folder = 'shots'
    fps = 25
    images = [img for img in os.listdir(shots_folder) if img.endswith(".png")]

    images = sorted(images)[:]
    frame = cv2.imread(os.path.join(shots_folder, images[0]))
    height, width, layers = frame.shape

    video = cv2.VideoWriter(video_path, cv2.VideoWriter_fourcc(*'mp4v'), fps, (width, height))

    for image in images:
        video.write(cv2.imread(os.path.join(shots_folder, image)))

    cv2.destroyAllWindows()
    video.release()

shots_folder = 'shots'
video_path = 'video.mp4'  
make_a_video(shots_folder, video_path)


  


• x86 : Remove inline MMX assembly that clobbers the FPU state

  26 janvier 2024, par Martin Storsjö

  x86 : Remove inline MMX assembly that clobbers the FPU state
  These inline implementations of AV_COPY64, AV_SWAP64 and AV_ZERO64
  
  are known to clobber the FPU state - which has to be restored
  
  with the 'emms' instruction afterwards.
  This was known and signaled with the FF_COPY_SWAP_ZERO_USES_MMX
  
  define, which calling code seems to have been supposed to check,
  
  in order to call emms_c() after using them. See
  
  0b1972d4096df5879038f0af776f87f41e90ebd4,
  
  29c4c0886d143790fcbeddbe40a23dfc6f56345c and
  
  df215e575850e41b19aeb1fd99e53372a6b3d537 for history on earlier
  
  fixes in the same area.
  However, new code can use these AV_*64() macros without knowing
  
  about the need to call emms_c().
  Just get rid of these dangerous inline assembly snippets ; this
  
  doesn't make any difference for 64 bit architectures anyway.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] libavcodec/dca_core.c
  • [DH] libavutil/x86/intreadwrite.h

• How to create a local audio livestream server with ffmpeg and python ? [closed]

  10 novembre 2024, par Fenekhu

  Simply put, this is what I'm trying to accomplish :
  
I navigate to something like http://localhost:8080/ in my browser and the browser shows a built-in audio player playing whatever the ffmpeg process is streaming. (Not just serving a local audio file.) (Built-in here meaning the page looks the same as if you had opened an mp3 file with your browser.)

  


  At first I thought it would be easy, as ffmpeg has the ability to stream through different protocols. I seem to have misunderstood though, because while I can stream something over rtp with it, I can't access that from my browser. Some stackoverflow questions I found seem to imply that you can do this with the output options -f mpegts http://localhost:8080, but when I try this, ffmpeg freezes for a second, then I get these errors :

  


  [tcp @ 00000210f70b0700] Connection to tcp://localhost:8080 failed: Error number -138 occurred
[out#0/mpegts @ 00000210f7080ec0] Error opening output http://localhost:8080: Error number -138 occurred
Error opening output file http://localhost:8080.
Error opening output files: Error number -138 occurred


  


  but I have no problem with -f rtp rtp://localhost:8080. (Like I said though, I can't access that through the browser).

  


  So I suspect I need something else to "pick up" the rtp stream and put it on an http server, but I haven't been able to find anything on that, probably because I just don't know the right thing to search. It seems like something that should be easily doable in Python, and that would be my preferred language to do it in over javascript, if possible.

  


  Can anyone point me in the right direction ? Or let me know if I'm misunderstanding something ? Thanks.