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• avcodec/pgxdec : Fix issue with negative linesizes

  15 avril 2022, par Andreas Rheinhardt

  avcodec/pgxdec : Fix issue with negative linesizes
  The PGX decoder accesses the lines via code like
  
  (PIXEL*)frame->data[0] + i*frame->linesize[0]/sizeof(PIXEL)
  
  where PIXEL is a macro parameter. This code has issues with negative
  
  linesizes, because the type of sizeof(PIXEL) is size_t, so
  
  that on common systems i*linesize/sizeof(PIXEL) will
  
  always be an unsigned type that is very large in case linesize is
  
  negative. This happens to work*, but it is undefined behaviour
  
  and e.g. leads to "src/libavcodec/pgxdec.c:114:1 : runtime error :
  
  addition of unsigned offset to 0x7efe9c2b7040 overflowed to 0x7efe9c2b6040"
  
  errors from UBSAN.
  
  Fix this by using (PIXEL*)(frame->data[0] + i*frame->linesize[0]).
  
  This is allowed because linesize has to be suitably aligned.
  * : Converting a negative int to size_t works by adding SIZE_MAX + 1
  
  to the number, so that the result is off by (SIZE_MAX + 1) /
  
  sizeof(PIXEL). Converting the pointer arithmetic (performed on PIXELs)
  
  back to ordinary pointers is tantamount to multiplying by sizeof(PIXEL),
  
  so that the result is off by SIZE_MAX + 1 ; but SIZE_MAX + 1 == 0
  
  for the underlying pointers.
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/pgxdec.c

• webM files shows green and purple effects on mobile

  11 octobre 2015, par Naveen Gamage

  I have converted several GIFs to webM files using ffmpeg on my Ubuntu 14.04 server.

  Heres the code I used for conversation.

  ffmpeg -i your_gif.gif -c:v libvpx -crf 12 -b:v 500K output.webm

  source https://gist.github.com/ndarville/10010916

  The problem is converted webM files shows perfectly fine on PCs but on my mobile it shows with green and purple shadows.

  PC

  

  Mobile

  

  I tried changing -crf and -b:v values to their max but nothing happens.

  webM file : http://d1pnsuxwa0it39.cloudfront.net/uploads/comments/webm/4673555.webm

  edit :

  also I can see webM files on some other sites fine. I think this has to do something with the way I convert files.

  edit :

  I have tried another code I found on stackoverflow but still the same.

  ffmpeg -f gif -i infile.gif outfile.mp4

  EDIT :

  If anyone think this has something to do with the way I installed FFMPEG, I followed the steps on FFMPEG official docs.

  https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu

  EDIT :

  Input file :

  http://d1pnsuxwa0it39.cloudfront.net/test/1.gif

  Output file :

  http://d1pnsuxwa0it39.cloudfront.net/test/output.webm

  FFMPEG CLI output

   /home/naveencg/bin/ffmpeg -i 1.gif -c:v libvpx -crf 12 -b:v 500K output.webm
  
  ffmpeg version 2.5.git Copyright (c) 2000-2014 the FFmpeg developers
  
    built on Dec 31 2014 14:37:15 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
  
    configuration: --prefix=/home/naveencg/ffmpeg_build --extra-cflags=-I/home/naveencg/ffmpeg_build/include --extra-ldflags=-L/home/naveencg/ffmpeg_build/lib --bindir=/home/naveencg/bin --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree
  
    libavutil      54. 15.100 / 54. 15.100
  
    libavcodec     56. 19.100 / 56. 19.100
  
    libavformat    56. 16.102 / 56. 16.102
  
    libavdevice    56.  3.100 / 56.  3.100
  
    libavfilter     5.  6.100 /  5.  6.100
  
    libswscale      3.  1.101 /  3.  1.101
  
    libswresample   1.  1.100 /  1.  1.100
  
    libpostproc    53.  3.100 / 53.  3.100
  
  Input #0, gif, from '1.gif':
  
    Duration: N/A, bitrate: N/A
  
      Stream #0:0: Video: gif, bgra, 350x169, 25 fps, 25 tbr, 100 tbn, 100 tbc
  
  [libvpx @ 0x1e2bf60] v1.3.0
  
  Output #0, webm, to 'output.webm':
  
    Metadata:
  
      encoder         : Lavf56.16.102
  
      Stream #0:0: Video: vp8 (libvpx), yuva420p, 350x169, q=-1--1, 500 kb/s, 25 fps, 1k tbn, 25 tbc
  
      Metadata:
  
        encoder         : Lavc56.19.100 libvpx
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (gif (native) -> vp8 (libvpx))
  
  Press [q] to stop, [?] for help
  
  frame=   21 fps=0.0 q=0.0 size=      58kB time=00:00:00.84 bitrate= 569.7kbits/sframe=   44 fps= 41 q=0.0 size=     110kB time=00:00:01.76 bitrate= 512.4kbits/sframe=   62 fps= 39 q=0.0 size=     153kB time=00:00:02.48 bitrate= 505.9kbits/sframe=   84 fps= 40 q=0.0 size=     210kB time=00:00:03.36 bitrate= 510.8kbits/sframe=   88 fps= 41 q=0.0 Lsize=     218kB time=00:00:03.52 bitrate= 508.3kbits/s
  
  video:216kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.971527%

• mlpdec : Fix a undefined left shift of negative number

  26 septembre 2015, par Ganesh Ajjanagadde

  mlpdec : Fix a undefined left shift of negative number
  This fixes a -Wshift-negative-value warning reported with clang 3.7+.
  Signed-off-by : Ganesh Ajjanagadde <gajjanagadde@gmail.com>
  

  • [DBH] libavcodec/mlpdec.c