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• avformat/matroskadec : Allow to count the number of element occurences

  16 février 2021, par Andreas Rheinhardt

  avformat/matroskadec : Allow to count the number of element occurences
  Up until now, the generic EBML reader used by the Matroska demuxer did
  
  not have the capability to record whether an element was actually
  
  present or not ; instead, in cases where it mattered one typically added
  
  an invalid default value and checked whether the value is valid (in
  
  which case it is guaranteed to be present). This worked pretty well so
  
  far, yet the EBML specifications have evolved : It is now legal to use
  
  zero-length elements for floats, ints, uints and strings (both ASCII and
  
  UTF-8) ; the value of these elements is the default value of the element
  
  (if it has one) or zero for scalar types and an empty string for
  
  strings. Furthermore, having a default value does no longer imply that
  
  the element may be presumed to be present (with its default value) if it
  
  is absent ; this is only true if the element is mandatory, too.
  These rules are designed to allow size savings as follows : Consider the
  
  newly added FlagOriginal : It being zero means the track is not in its
  
  original language, it being one means it is. For backward compatibility
  
  reasons, neither of the two values may be inferred automatically in the
  
  absence of the element. But one can still save a byte when one wants to
  
  write the element with a value of zero, as one can write the integer with
  
  a length of zero : 0x55AE 80 instead of 0x55AE 81 00. In the former case,
  
  a parser has to infer the value of the element to be zero (which is the
  
  element's default value).
  When encountering an element with length zero, our parser always infers
  
  a value of zero (or an empty string) ; this is wrong for values with
  
  a different default value. It needs to infer the default value (or zero
  
  in its absence) and this precludes using an invalid default value for
  
  elements like FlagOriginal. Ergo one needs to be able to record whether
  
  an element is present or not by other means. This patch allows to use a
  
  simple counter for this. While just at it, some invalid and unnecessary
  
  default values have been removed (mastering metadata elements used
  
  default values of -1.0, despite these elements only being used if they
  
  are > 0).
  Reviewed-by : Ridley Combs <rcombs@rcombs.me>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskadec.c

• Revision 28201 : - chaine le langue manquante

  28 avril 2009, par marcimat@… — Log

   chaine le langue manquante

• Revision 36889 : Le début d’une page d’info concernant la configuration de FFMPEG sur le ...

  3 avril 2010, par kent1@… — Log

  Le début d’une page d’info concernant la configuration de FFMPEG sur le serveur.
  On vire le PHP du squelette du formulaire de configuration
  On prépare le passage aux pressets