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• Python Av encode result is empty always

  19 septembre 2023, par Emir evcil

  I'm quite a newbie when it comes to ffmpeg and av, I was trying to do a simple encode - decode example but the encode result always returns an empty list. I don't understand the reason for this, I don't know how it can be solved.

  


  import av
import numpy as np
import cv2 

container = av.open(file = "video=PC Camera",format = "dshow",options = {"video_size":"640x480"},mode = "r")

def getFrame():
    # open camera
    for frame in container.decode(video=0):
        yield frame
        
def encode(frame):
    encoder = av.CodecContext.create('h264', 'w')
    encoder.width = frame.width
    encoder.height = frame.height
    encoder.pix_fmt = frame.format.name
    encoder.bit_rate = 5000000
    encoder.framerate = 30
    encoder.open()
    frames = encoder.encode(frame)
    encoder.close()
    return frames
    
    
if __name__ == "__main__":
    while 1:
        frame = next(getFrame())
        frame_encoded = encode(frame)
        print(frame_encoded) // always empty
        if len(frame_encoded) == 0:
            continue
        #cv2.imshow("frame",frame.to_ndarray(format = "bgr24"))
        #cv2.waitKey(1)


  


• Empty output when extracting frames with FFMPEG at specific timestamps taken from FFPROBE

  9 octobre 2023, par Andrew McDowell

  I am trying to extract frames from a video as close as possible to specific timestamps, but for some timestamps I'm getting no output.

  


  I'm first using ffprobe to get a list of all frames along with their time values :

  


  ffprobe -select_streams v -show_frames -show_entries frame=pts_time,pkt_pts_time,pict_type <input video="video" />

  


  Which gives me an output like :

  


  [FRAME]
pts_time=11.950000
pict_type=I
[/FRAME]
[FRAME]
pts_time=11.966667
pict_type=B
[/FRAME]
[FRAME]
pts_time=11.983333
pict_type=P
[/FRAME]


  


  I'm then parsing this and determining which frame is the closest to the time I want and using FFmpeg to extract frames which match the chosen times like so :

  


  ffmpeg -i <input video="video" /> -filter:v "select=&#x27;eq(t, 11.950000)&#x2B;eq(t, 11.983333)&#x27;" -vsync drop -start_number 0 <output path="path">/frame-%08d.png</output>

  


  This mostly works but I've noticed for some frames I get no output. From some testing it always seems to work for I frames and works occasionally for P or B frames but not always.

  


  I can't see any pattern to which frames it works for or not and would love an insight into whether I'm doing something wrong in the extraction, or whether there's a way to determine which frames can be extracted or not.

  


• avutil/x86/pixelutils : Empty MMX state in ff_pixelutils_sad_8x8_mmxext

  1er novembre 2023, par Andreas Rheinhardt

  avutil/x86/pixelutils : Empty MMX state in ff_pixelutils_sad_8x8_mmxext
  We currently mostly do not empty the MMX state in our MMX
  
  DSP functions ; instead we only do so before code that might
  
  be using x87 code. This is a violation of the System V i386 ABI
  
  (and maybe of other ABIs, too) :
  
  "The CPU shall be in x87 mode upon entry to a function. Therefore,
  
  every function that uses the MMX registers is required to issue an
  
  emms or femms instruction after using MMX registers, before returning
  
  or calling another function." (See 2.2.1 in [1])
  
  This patch does not intend to change all these functions to abide
  
  by the ABI ; it only does so for ff_pixelutils_sad_8x8_mmxext, as this
  
  function can by called by external users, because it is exported
  
  via the pixelutils API. Without this, the following fragment will
  
  assert (on x86/x64) :
  
      uint8_t src1[8 * 8], src2[8 * 8] ;
  
      av_pixelutils_sad_fn fn = av_pixelutils_get_sad_fn(3, 3, 0, NULL) ;
  
      fn(src1, 8, src2, 8) ;
  
      av_assert0_fpu() ;
  [1] : https://raw.githubusercontent.com/wiki/hjl-tools/x86-psABI/intel386-psABI-1.1.pdf
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavutil/x86/pixelutils.asm