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• avformat/matroskaenc : Avoid unnecessary seek

  2 mai 2020, par Andreas Rheinhardt

  avformat/matroskaenc : Avoid unnecessary seek
  The Matroska muxer has a pair of functions designed to write master
  
  elements whose exact length is not known in advance : start_ebml_master()
  
  and end_ebml_master(). The first one of these would write the EBML ID of
  
  the master element that is about to be started, reserve some bytes for
  
  the length field and record the current position as well as how many
  
  bytes were used for the length field. When writing the master's contents
  
  is finished, end_ebml_master() gets the current position (at the end of
  
  the master element), seeks to the length field using the recorded
  
  position, writes the length field and seeks back to the end of the
  
  master element so that one can continue writing other elements.
  But if one wants to modify the content of the master element itself,
  
  then the seek back is superfluous. This is the scenario that presents
  
  itself when writing the trailer : One wants to update several elements
  
  contained in the Segment master element (this is the main/root master
  
  element of a Matroska file) that were already written when writing the
  
  header. The current approach is to seek to the beginning of the file
  
  to update the elements, then seek to the end, call end_ebml_master()
  
  which immediately seeks to the beginning to write the length and seeks
  
  back. The seek to the end (which has only been performed because
  
  end_ebml_master() uses the initial position to determine the length
  
  of the master element) and the seek back are of course superfluous.
  This commit avoids these seeks by no longer using start/end_ebml_master()
  
  to write the segment's length field. Instead, it is now written
  
  manually. The new approach is : Seek to the beginning to write the length
  
  field, then update the elements (in the order they appear in the file)
  
  and seek back to the end.
  This reduces the ordinary amount of seeks of the Matroska muxer to two
  
  (ordinary excludes scenarios where one has big Chapters or Attachments
  
  or where one writes the Cues at the front).
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• avformat/matroskaenc : Simplify writing Void elements

  12 janvier 2020, par Andreas Rheinhardt

  avformat/matroskaenc : Simplify writing Void elements
  Reserving space in Matroska works by writing a Void element. And until
  
  now this worked as follows : The current position was recorded and the
  
  EBML ID as well as the length field written ; then the new position was
  
  recorded to know how much more to write. Afterwards the actual writing
  
  has been performed via ffio_fill().
  But it is unnecessary to explicitly use the positions (obtained via
  
  avio_tell()) to find out how much still needs to be written, because the
  
  length of the ID and the length field are known. So rewrite the function
  
  to no longer use them.
  Also, given that ffio_fill() uses an int parameter and given that no
  
  current caller (and no sane future caller) will want to reserve several
  
  GB of space, make the size parameter of put_ebml_void() itself an int.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• Révision 116004 : Extension des filtres |image_xx a SVG :

  18 juillet 2019, par cedric@yterium.com

  |image_reduire
  |image_passe_partout
  |image_recadre
  |image_aplatir (conserve un svg mais applique le background)
  |image_format (conserve un svg mais applique le background)
  |image_alpha
  |image_flip_vertical
  |image_flip_horizontal
  |image_flou
  |image_nb
  |image_sepia
  |image_gamma
  |image_rotation
  |couleur_extraire (extrait une moyenne des couleurs referencees dans le SVG, sans notion de leur importance visuelle)

  avec la réserve que pour certains filtres (flou, sepia, nb) il faut que le navigateur supporte bien les CSS filters dans les SVG :seul FF le supporte actuellement - dans les navigateurs qui ne le supportent pas l’effet est juste ignoré.
  (Il semble être possible d’utiliser des features filter avancées des SVG qui sont mieux supportées mais je n’ai pas creusé dans cette voie)

  les filtres qui ne supportent pas le SVG (et sont donc sans effet) sont :

  |image_masque (on devrait pouvoir porter une partie des fonctionnalités mais c’est plus compliqué)
  |image_renforcement (sans objet ?)
  |image_fond_transparent (sans objet)
  |image_imagick (sans objet)
  |image_recadre_mini (sans objet)