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• 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 ?

• 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 ?

• http: fix potentially dangerous whitespace skipping code

  8 mars 2018, par wm4

  http: fix potentially dangerous whitespace skipping code
  If the string consists entirely of whitespace, this could in theory
  
  continue to write '\0' before the start of the memory allocation. In
  
  practice, it didn't really happen : the generic HTTP header parsing code
  
  already skips leading whitespaces, so the string is either empty, or
  
  consists a non-whitespace. (The generic code and the cookie code
  
  actually have different ideas about what bytes are whitespace : the
  
  former uses av_isspace(), the latter uses WHITESPACES. Fortunately,
  
  av_isspace() is a super set of the http.c specific WHITESPACES, so
  
  there's probably no case where the above assumption could have been
  
  broken.)
  

  • [DH] libavformat/http.c