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• lavc/vvc : Use a bitfield to store MIP information

  3 décembre 2024, par Frank Plowman

  lavc/vvc : Use a bitfield to store MIP information
  Reduces memory consumption by 4MB for 1080p video with a maximum delay
  
  of 16 frames by packing various information related to MIP :
  
  * intra_mip_flag, 1 bit
  
  * intra_mip_transposed_flag, 1 bit
  
  * intra_mip_mode, 4 bits
  
  Into a single byte.
  Co-authored-by : Nuo Mi <nuomi2021@gmail.com>
  
  Signed-off-by : Frank Plowman <post@frankplowman.com>
  

  • [DH] libavcodec/vvc/cabac.c
  • [DH] libavcodec/vvc/ctu.c
  • [DH] libavcodec/vvc/dec.c
  • [DH] libavcodec/vvc/dec.h
  • [DH] libavcodec/vvc/dsp.c
  • [DH] libavcodec/vvc/intra_template.c

• lavc/vvc : Fix emulation prevention byte handling

  26 janvier 2024, par Frank Plowman

  lavc/vvc : Fix emulation prevention byte handling
  nal->skipped_bytes_pos contains the positions of errors relative to the
  
  start of the slice header, whereas the position they were tested against
  
  is relative to the start of the slice data, i.e. one byte after the end
  
  of the slice header.
  Patch fixes this by storing the size of the slice header in H266RawSlice
  
  and adding it to the position given by the GetBitContext before
  
  comparing to skipped_bytes_pos.  This fixes AVERROR_INVALIDDATAs for
  
  various valid bitstreams, such as the LMCS_B_Dolby_2 conformance
  
  bitstream.
  Signed-off-by : Frank Plowman <post@frankplowman.com>
  

  • [DH] libavcodec/cbs_h2645.c
  • [DH] libavcodec/cbs_h266.h
  • [DH] libavcodec/vvc/vvcdec.c

• lavc/vvc : Check slice structure

  10 janvier, par Frank Plowman

  lavc/vvc : Check slice structure
  The criteria for slice structure validity is similar to that of
  
  subpicture structure validity that we saw not too long ago [1].
  
  The relationship between tiles and slices must satisfy the following
  
  properties :
  * Exhaustivity.  All tiles in a picture must belong to a slice.  The
  
    tiles cover the picture, so this implies the slices must cover the
  
    picture.
  
  * Mutual exclusivity.  No tile may belong to more than one slice, i.e.
  
    slices may not overlap.
  In most cases these properties are guaranteed by the syntax.  There is
  
  one noticable exception however : when pps_tile_idx_delta_present_flag is
  
  equal to one, each slice is associated with a syntax element
  
  pps_tile_idx_delta_val[i] which "specifies the difference between the
  
  tile index of the tile containing the first CTU in the ( i + 1 )-th
  
  rectangular slice and the tile index of the tile containing the first
  
  CTU in the i-th rectangular slice" [2].  When these syntax elements are
  
  present, the i-th slice can begin anywhere and the usual guarantees
  
  provided by the syntax are lost.
  The patch detects slice structures which violate either of the two
  
  properties above, and are therefore invalid, while building the
  
  slice map.  Should the slice map be determined to be invalid, an
  
  AVERROR_INVALIDDATA is returned.  This prevents issues including
  
  segmentation faults when trying to decode,  invalid bitstreams.
  [1] : https://ffmpeg.org//pipermail/ffmpeg-devel/2024-October/334470.html
  
  [2] : H.266 (V3) Section 7.4.3.5, Picture parameter set RBSP semantics
  Signed-off-by : Frank Plowman <post@frankplowman.com>
  

  • [DH] libavcodec/vvc/ps.c