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• ffmpeg - Retriving video macroblock info with -debug mb_type command

  14 juin 2018, par fabridigua

  I am trying to get the information about all the macroblocks in the frames of a video (mp4).
  In particular i’m using the ffmpeg command :

  ffmpeg -debug mb_type -i input.mp4 out.mp4 2> macroblocks.txt

  It seams to work fine, but... i don’t understand how to parse the output !

  I see that after many uninteresting writings, starts a group of blocks starting with

  "New frame, type : [FRAME TYPE]"

  so I assume that these are the blocks referring to each frame containing the type of each macroblock.. but what mean the symbols inside ?

  New frame, type : B [h264 @ 000001c0241c1cc0] d < X- < I > > > >
  X d d d d d < < d < d > < d d > d < d d d < > <
  d < > X < d d > d X d < > d X d > > d d+ d

  From the theory I know that there are intra or predicted macroblocks, but i don’t understand how parse this info from the "New frame"-blocks.

  • What mean i,I,A,<,>,X,|,etc.?

  Also often there are sentences like

  nal_unit_type : 1(Coded slice of a non-IDR picture), nal_ref_idc : 2

  or

  cur_dts is invalid (this is harmless if it occurs once at the start
  per stream)

  that i really don’t understand...
  I can’t too find a documentation..
  Can anyone help me ?

• ffmpeg - Retrieving video macroblock info with -debug mb_type command

  18 juin 2018, par fabridigua

  I am trying to get the information about all the macroblocks in the frames of a video (mp4).
  In particular i’m using the ffmpeg command :

  ffmpeg -debug mb_type -i input.mp4 out.mp4 2> macroblocks.txt

  It seems to work fine, but... i don’t understand how to parse the output !

  I see that after many uninteresting writings, starts a group of blocks starting with

  "New frame, type : [FRAME TYPE]"

  so I assume that these are the blocks referring to each frame containing the type of each macroblock.. but what do the symbols inside mean ?

  New frame, type : B [h264 @ 000001c0241c1cc0] d < X- < I > > > >
  X d d d d d < < d < d > < d d > d < d d d < > <
  d < > X < d d > d X d < > d X d > > d d+ d

  From the theory I know that there are intra or predicted macroblocks, but i don’t understand how to parse this info from the "New frame"-blocks.

  • What means i,I,A,<,>,X,|,etc.?

  Also often there are sentences like

  nal_unit_type : 1(Coded slice of a non-IDR picture), nal_ref_idc : 2

  or

  cur_dts is invalid (this is harmless if it occurs once at the start
  per stream)

  that i really don’t understand...
  I can’t too find a documentation..
  Can anyone help me ?

• Python - getting duration of a video with ffprobe and splitting the video into pieces

  22 octobre 2018, par ZelelB

  I am trying to split a video with ffmpeg, implementing a python script.

  I am getting this error :

  Command '['ffprobe', '-i', 'path_to_my_video/MVI_0731.MP4', '-hide_banner']' returned non-zero exit status 1.

  Here is the code I am using to split the video :

  for video_file in video_files:
  
          try:
  
              # Call "ffprobe" to get duration of input video.
  
              ffprobe_process = subprocess.run(args=["ffprobe", "-i", video_file, "-hide_banner"],
  
                                             check=True,
  
                                             stdout=subprocess.PIPE,
  
                                             stderr=subprocess.PIPE,
  
                                             encoding="utf-8",
  
                                             shell=True)
  
  
  
              # "ffprobe" writes to stderr instead of stdout!
  
              duration_string = extract_duration_from_ffprobe_output(ffprobe_process.stderr)            
  
              duration_in_seconds = duration_string_to_seconds(duration_string)
  
  
  
              # Make start_stop_list
  
              start_stop_list = read_start_stop_list(start_stop_lists[nbr_video])
  
              nbr_video += 1
  
              total_pieces = int(len(start_stop_list))

  This is the line causing the problem :

  ffprobe_process = subprocess.run(args=["ffprobe", "-i", video_file, "-hide_banner"],
  
                                             check=True,
  
                                             stdout=subprocess.PIPE,
  
                                             stderr=subprocess.PIPE,
  
                                             encoding="utf-8",
  
                                             shell=True)

  When I change it to this line of code :

  ffprobe_process = subprocess.run(args=['ffprobe', '-i', video_file, '-show_entries', 'format=duration', '-v', 'quiet', '-of', 'csv=%s' % ("p=0")])

  it works, I mean, the script goes after that line, but then throws the following error at the next line :

  470.240000
  
  expected string or bytes-like object

  470.240000 is the right duration of my video. So the new line that I changed it with works better, but still not working with my code somehow.

  Anyone has an idea how I can solve this ?