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• avcodec/flac_parser : Use native endianness when possible

  6 octobre 2019, par Andreas Rheinhardt

  avcodec/flac_parser : Use native endianness when possible
  FLAC sync codes contain a byte equal to 0xFF and so the function that
  
  searches for sync codes first searched for this byte. It did this by
  
  checking four bytes at once ; these bytes have been read via AV_RB32, but
  
  the test works just as well with native endianness.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/flac_parser.c

• avcodec/utvideodec : Avoid qsort when creating Huffman tables

  24 septembre 2020, par Andreas Rheinhardt

  avcodec/utvideodec : Avoid qsort when creating Huffman tables
  The Ut video format uses Huffman trees which are only implicitly coded
  
  in the bitstream : Only the lengths of the codes are coded, the rest has
  
  to be inferred by the decoder according to the rule that the longer
  
  codes are to the left of shorter codes in the tree and on each level the
  
  symbols are descending from left to right.
  Because longer codes are to the left of shorter codes, one needs to know
  
  how many non-leaf nodes there are on each level in order to know the
  
  code of the next left-most leaf (which belongs to the highest symbol on
  
  that level). The current code does this by sorting the entries to be
  
  ascending according to length and (for entries with the same length)
  
  ascending according to their symbols. This array is then traversed in
  
  reverse order, so that the lowest level is dealt with first, so that the
  
  number of non-leaf nodes of the next higher level is known when
  
  processing said level.
  But this can also be calculated without sorting : Simply count how many
  
  leaf nodes there are on each level. Then one can calculate the number of
  
  non-leaf nodes on each level iteratively from the lowest level upwards :
  
  It is just half the number of nodes of the level below.
  This improves performance : For the sample from ticket #4044 the amount
  
  of decicycles for one call to build_huff() decreased from 1055489 to
  
  446310 for Clang 10 and from 1080306 to 535155 for GCC 9.
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/utvideo.c
  • [DH] libavcodec/utvideo.h
  • [DH] libavcodec/utvideodec.c

• lavc/jpegtables : Handle multiple mappings to the same value

  29 août 2019, par Nick Renieris

  lavc/jpegtables : Handle multiple mappings to the same value
  Some JPEGs [1] have incorrect DHT entries that map 2 codes to
  
  the same value.
  The second (last) mapping does not ever actually appear in the
  
  code stream, therefore ignoring any mappings after the first one
  
  fixes this.
  Without this, an "mjpeg_decode_dc : bad vlc : 0:0" error is thrown.
  In all known files, the 2 codes are mapped to symbol 0 so only
  
  that case is checked.
  [1] : Embedded JPEGs in "X7 RAW" and "X7 CinemaDNG" samples here :
  
       https://www.dji.com/gr/zenmuse-x7/info#downloads
  Signed-off-by : Nick Renieris <velocityra@gmail.com>
  

  • [DH] libavcodec/jpegtables.c