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• Revision 1bd69ac57f : Fixing out of bounds access in frame_refs[] array. Change-Id : I08f45573e0b2195c

  30 janvier 2014, par Dmitry Kovalev

  Changed Paths :
   Modify /vp9/encoder/vp9_onyx_int.h

  
  
  Fixing out of bounds access in frame_refs[] array.

  Change-Id : I08f45573e0b2195c09fb6aecacb4c57431a711ea

• libavfilter/scale2ref : Fix out-of-bounds array access

  3 juin 2017, par Kevin Mark

  libavfilter/scale2ref : Fix out-of-bounds array access
  ff_scale_eval_dimensions blindly assumes that two inputs are always
  
  available as of 3385989b98be7940044e4f0a6b431a0a00abf2fa. This is
  
  notably not the case when the function is called for the scale
  
  filter. With the scale filter inputs[1] does not exist.
  ff_scale_eval_dimensions now has an updated scale2ref check that
  
  makes certain two inputs are actually available before attempting to
  
  access the second one.
  Thanks to James Almer for reporting this bug. This should fix the 820
  
  Valgrind tests I single-handedly managed to break.
  Signed-off-by : Kevin Mark <kmark937@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavfilter/scale.c

• CGO : How to access a C pointer array from Golang

  24 avril 2018, par nevernew

  I’m writing an app for the windows platform using FFmpeg and it’s golang wrapper goav, but I’m having trouble understanding how to use the C pointers to gain access to an array.

  I’m trying to get the streams stored in the AVFormatContext class to use in go, and eventually add frames to a texture in OpenGl to make a video player with cool transitions.

  I think understanding how to cast and access the C data will make coding this a lot easier.

  I’ve stripped out all the relevant parts of the C code, the wrapper and my code, shown below :

  C code - libavformat/avformat.h

  typedef struct AVFormatContext { 
  
      unsigned int nb_streams; 
  
      AVStream **streams; 
  
  }

  Golang goav wrapper

  package avutil
  
  
  
  //#cgo pkg-config: libavformat
  
  //#include <libavformat></libavformat>avformat.h>
  
  import "C"
  
  import (
  
      "unsafe"
  
  )
  
  
  
  type Context C.struct_AVFormatContext; 
  
  
  
  func (ctxt *Context) StreamsGet(i uintptr) *Stream {
  
      streams := (**Stream)(unsafe.Pointer(ctxt.streams));
  
      // I think this is where it's going wrong, I'm brand new to this stuff 
  
      return (*Stream)(unsafe.Pointer(uintptr(unsafe.Pointer(streams)) + i*unsafe.Sizeof(*streams)));
  
  }

  My Golang code

  package main
  
  
  
  import "github.com/giorgisio/goav/avformat"
  
  
  
  func main() {
  
      ctx := &avformat.Context{} // the actual function to initiate this does an mallocz for the streams
  
  
  
      stream := ctx.StreamsGet(0)
  
  
  
      //do stuff with stream...
  
  }

  In C it looks like I just have to do just streams[i], but that wont work in go, so I added a function to the wrapper using the technique from my question here.
  However I’m not getting the data ; It looks like I’m getting a pointer to somewhere random in memory. So, how can I access these elements form golang ? Any resources would be helpful too ; I’m going to be investing a fair bit of time into this.