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• avformat/matroskaenc : Don't use stream side-data size

  21 mai 2020, par Andreas Rheinhardt

  avformat/matroskaenc : Don't use stream side-data size
  av_stream_get_side_data() tells the caller whether a stream has side
  
  data of a specific type ; if present it can also tell the caller the size
  
  of the side data via an optional argument. The Matroska muxer always
  
  used this optional argument, although it doesn't really need the size,
  
  as the relevant side-data are not buffers, but structures. So change
  
  this.
  Furthermore, relying on the size also made the code susceptible to
  
  a quirk of av_stream_get_side_data() : It only sets the size argument if
  
  it found side data of the desired type. mkv_write_video_color() checks
  
  for side-data twice with the same variable for the size without resetting
  
  the size in between ; if the second type of side-data isn't present, the
  
  size will still be what it was after the first call. This was not
  
  dangerous in practice, as the check for the existence of the second
  
  side-data compared the size with the expected size, so it would only be
  
  problematic if lots of elements were to be added to AVContentLightMetadata.
  Reviewed-by : James Almer <jamrial@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• FFMPEG + Python - skipping unneeded frames on ffmpeg side

  11 mai 2020, par user3518753

  I'm trying to process a live hlsv stream, extract every 100th frame from it, and process it using openCV.

  



  Currently my code looks something like this :

  



  pipe = subprocess.Popen([FFMPEG_BIN, "-i", src, 
                    "-loglevel", "quiet",
                    "-an", 
                    "-f", "image2pipe",
                    "-pix_fmt", "bgr24",
                    "-vcodec", "rawvideo", "-"],
                    stdin=subprocess.PIPE, 
                    stdout=subprocess.PIPE, 
                    stderr=subprocess.DEVNULL)

while True:
    raw_image = pipe.stdout.read(WIDTH * HEIGHT * 3)
    if frame_counter > 100:
        frame_counter = 0
        process_frame(raw_image)
    frame_counter += 1


  



  Reading all the frames and dumping 99% of them seems inefficient, and has led me to pipe buffer issues (at least I suspect that).

  



  Is it possible to skip the frames in FFMPEG, so that every 100th frame will go to the stdout ?

  


• How do I preserve side data when concatenating files in ffmpeg ?

  28 mai 2020, par Mark Kahn

  I have multiple 360 videos that I'm trying to concatenate in ffmpeg. The command it self is pretty straightforward :

  



  ffmpeg -f concat -i 0036_concat.txt -c copy -strict unofficial 36.mp4


  



  where 0036_concat.txt is just a list of the individual files. The issue I'm having is that I can't get ffmpeg to preserve side data. Very simply put, ffprobe on any of the source files includes this :

  



  Side data:
  spherical: equirectangular (0.000000/0.000000/0.000000)


  



  And I can't, for the life of me, get that to propagate to the output file.

  



  this question has a solution that works for single files, but it doesn't work when concatenating multiple files.

  



  I'd be perfectly fine injecting that entire string if anyone knows how.