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• ffmpeg-python extracting frames from camera in batches

  28 juin 2021, par Alter

  When I read frames from my camera using ffmpeg-python, the frames appear to come in batches of 4- why is this, and how can I change it ?

  


  I would like to get one frame at a time... I'm also hoping to avoid faking the frame times using the -r option

  


  

  


  In the image above, I'm recording at 30fps. The 120ms pause followed by 3 quick frames suggests that the frames are coming in batches of 4.

  


  Partial code

  


  reader = (ffmpeg
    .input('/dev/video0', framerate=fps)
    .output('pipe:', format='rawvideo', pix_fmt='rgb24')
    .run_async(pipe_stdout=True))
    
while True:
    start = time.time_ns()
    frame = reader.stdout.read(width * height * 3)
    logger.debug(f'frame read time: {(time.time_ns() - start)/1e6}ms')
    # Do something else
    logger.debug(f'frame capture loop: {(time.time_ns() - start)/1e6}ms')


  


• Merge commit ’f046c3b5ac36848cce824b008e0347c621523041’

  3 juillet 2015, par Michael Niedermayer

  Merge commit ’f046c3b5ac36848cce824b008e0347c621523041’
  * commit ’f046c3b5ac36848cce824b008e0347c621523041’ :
  
    lavc : Move deprecation warning disabling to files including the table
  
    lavc : Disable deprectation warnings coming from options table
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/options.c
  • [DH] libavformat/options.c

• RGB to YUV422 conversion with ffmpeg, incorrect colors

  22 janvier 2016, par user3578571

  I’m trying to convert an 8bit RGB uncompressed to an mpeg2 mxf file (xdcam 422 HD 1080 50i) which is YUV422. With info from the FFMpeg docs and various websites i made the following command :

  ./ffmpeg -y -i test_lines.mov  -pix_fmt yuv422p -vcodec mpeg2video -non_linear_quant 1 -flags +ildct+ilme -top 1 -dc 10 -intra_vlc 1 -qmax 2 -vtag xd5c -rc_max_vbv_use 1 -rc_min_vbv_use 1 -g 12 -b:v 50000k -minrate 50000k -maxrate 50000k -bufsize 8000k -acodec pcm_s24le -ar 48000 -bf 2 -ac 2 lines_HD.mxf

  This gave me a result with the colors much brighter than the original.

  So i tried adding the options -color_range 1 -colorspace 1 -color_primaries 1 -color_trc 1 but this didn’t seem to do anything.

  After adding colormatrix=bt601:bt709 i got a way better image, but slightly darker than the original and it also feels weird specifying this option cause the source is also in the REC709 colorspace, so why specify it differently ?

  Next i regenerated my source image to an YUV codec (prores) and rerun FFMpeg on it with the colors coming out just fine. Therefore i think it has to be an RGB -> YUV problem.
  Does somebody have an idea how to this properly ? I can provide screenshots of the different results on a videoscope as soon as i’m back at the office, if anybody is interested.

  Last, i know there are various topics touching this subject but either they go way over my head FFmpeg wise or bring me to the stage where i already am.