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• avutil/aes : Don't use misaligned pointers

  21 octobre 2022, par Andreas Rheinhardt

  avutil/aes : Don't use misaligned pointers
  The AES code uses av_aes_block, a union consisting of
  
  uint64_t[2], uint32_t[4], uint8_t[4][4] and uint8_t[16].
  
  subshift() performs byte-wise manipulations of two av_aes_blocks,
  
  but when encrypting, it does so with a shift of two bytes ;
  
  more precisely, it uses
  
  "av_aes_block *s1 = (av_aes_block *) (s0[0].u8 - s)"
  
  and lateron uses the uint8_t[16] member to access s0.
  
  Yet av_aes_block requires to be suitably aligned for
  
  the uint64_t[2] member, which s0[0].u8 - 2 is certainly
  
  not. This is in violation of 6.3.2.3 (7) of C11. UBSan
  
  reports this in the aes_ctr, mov-3elist-encrypted,
  
  mov-frag-encrypted, mov-tenc-only-encrypted and srtp
  
  tests.
  
  Furthermore, there is another issue here : The pointer points
  
  outside of s0 ; this works, because all the accesses lateron
  
  use an index >= 3. (Clang-)UBSan reports this as
  
  "runtime error : index -2 out of bounds for type 'uint8_t[16]'".
  This commit fixes both of these issues : The latter issue
  
  is fixed by applying an offset of "+ 3" during the cast
  
  and subtracting this from the indices used lateron.
  
  The former issue is solved by not casting to av_aes_block*
  
  at all ; instead simply cast to unsigned char*.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavutil/aes.c

• ffmpeg blend multiple files

  7 octobre 2022, par Gregory

  I currently have the following command that allows me to overlay files and apply a blending mode. This works well when I overlay 2 files, however when I try to overlay a third image, then the generated output is incorrect.

  


  

  • Blue

  


  • GroundShadow (softlight)

  


  • FeetShadows (multiply)

  


  


  Command :

  


  ffmpeg \
    -i /Users/me/Downloads/blue.gif \
    -i /Users/me/Downloads/GroundShadow.gif \
    -i /Users/me/Downloads/FeetShadows.gif \
    -y \
    -filter_complex "[0:v][1:v]blend=all_mode='softlight'[v1],[v1][2:v]blend=all_mode='multiply'[v2],[v2]split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" \
    /Users/me/Downloads/preview.gif


  


  





  


  


  


  


  



  


  


  


  


  Expected (ignore that it's animated)	Result

  


  


  The background color is washed for some reason.
I'm not sure if i'm applying the blending filters in the right order or if you should split between the images to then apply the blend ? Or something else ?

  


• Merge commit ’8ddfa5ae5ef64a25dd087d74954ebdb9081f0d67’

  31 mars 2017, par James Almer

  Merge commit ’8ddfa5ae5ef64a25dd087d74954ebdb9081f0d67’
  * commit ’8ddfa5ae5ef64a25dd087d74954ebdb9081f0d67’ :
  
    vf_drawtext : Drop wrong void* cast
  This commit is a noop, see 4c96985af1b8870482b6b6ef9120960633f62cee
  Merged-by : James Almer <jamrial@gmail.com>