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• the srcSliceY parameter in sws_scale function of ffmpeg library

  12 août 2017, par dafnahaktana

  Almost everywhere I looked, the srcSliceY value is set to 0.
  In the documentation it is wrriten :

  c            the scaling context previously created with sws_getContext()
  
  srcSlice    the array containing the pointers to the planes of the source slice
  
  srcStride   the array containing the strides for each plane of the source image
  
  srcSliceY   the position in the source image of the slice to process, that is the number (counted starting from zero) in the image of the first row of the slice
  
  ...

  It is unclear to me what it means "the source image". Does it mean the source slice ? There is no parameter called "source image".

  I wrote this code :

  SwsContext *ctx = sws_getContext(width, height, AV_PIX_FMT_GRAY8,
  
                                           dwidth, dheight, AV_PIX_FMT_GRAY8,
  
                                           SWS_BILINEAR, NULL, NULL, NULL);
  
  
  
  
  
  const uint8_t* srcSlice[1] = { pSrc};
  
  const int srcStride[1] = { width };
  
  int srcSliceH = height;
  
  const int   dstStride[1] = { dwidth };
  
  
  
  printf("srcStride=%d, height =%d\n",srcStride[0],srcSliceH);
  
  for(int i=0;i<100;i++){
  
    int t = sws_scale(ctx, srcSlice, srcStride, i, srcSliceH, &pDst, dstStride);
  
    if(t != 0)
  
      printf("i=%d t= %d\n",i,t);
  
  }

  I get the output :

  srcStride=384, height =30
  
  [swscaler @ 0x1b0ba60] Warning: data is not aligned! This can lead to a speedloss
  
  i=0 t= 2
  
  i=4 t= 1
  
  i=14 t= 1
  
  i=24 t= 1
  
  i=33 t= 1
  
  i=43 t= 1
  
  i=52 t= 1
  
  i=62 t= 1
  
  i=72 t= 1
  
  i=81 t= 1
  
  i=91 t= 1

  Looking at the source code of sws_scale, it returns 0 upon error or invalid input. So I conclude that for most values of srcSliceY in the iteration the sws_returns error. But it is unclear what is valid.

• utvideodec : Prevent possible signed overflow

  23 février 2016, par Ganesh Ajjanagadde

  utvideodec : Prevent possible signed overflow
  Doing slice_end - slice_start is unsafe and can lead to undefined behavior
  
  until slice_end has been properly sanitized.
  Reviewed-by : Ronald S. Bultje <rsbultje@gmail.com>
  
  Signed-off-by : Ganesh Ajjanagadde <gajjanag@gmail.com>
  
  Signed-off-by : Luca Barbato <lu_zero@gentoo.org>
  

  • [DBH] libavcodec/utvideodec.c

• pthread_frame : fix uninitialized variable read

  27 mars 2017, par wm4

  pthread_frame : fix uninitialized variable read
  Could lead to random behavior. This possibly happened due to commit
  
  32a5b631267. This should/could probably be simplified, but for no apply
  
  a minimal fix to quell the errors.
  Tested-by : Michael Niedermayer <michael@niedermayer.cc>
  
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/pthread_frame.c