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• avformat/mlvdec : Only store dimensions after having validated them

  10 août 2020, par Andreas Rheinhardt

  avformat/mlvdec : Only store dimensions after having validated them
  Otherwise it might happen that invalid dimensions are used when reading
  
  a video packet ; this might lead to undefined overflow.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/mlvdec.c

• avcodec/put_bits : Make skip_put_bits() less dangerous

  31 juillet 2020, par Andreas Rheinhardt

  avcodec/put_bits : Make skip_put_bits() less dangerous
  Before c63c303a1f2b58677d480505ec93a90f77dd25b5 (the commit which
  
  introduced a typedef for the type of the buffer of a PutBitContext)
  
  skip_put_bits() was as follows :
  static inline void skip_put_bits(PutBitContext *s, int n)
  
  
  
      s->bit_left -= n ;
  
      s->buf_ptr  -= 4 * (s->bit_left >> 5) ;
  
      s->bit_left &= 31 ;
  
  
  If s->bit_left was negative after the first subtraction, then the next
  
  line will divide this by 32 with rounding towards -inf and multiply by
  
  four ; the result will be negative, of course.
  The aforementioned commit changed this to :
  static inline void skip_put_bits(PutBitContext *s, int n)
  
  
  
      s->bit_left -= n ;
  
      s->buf_ptr  -= sizeof(BitBuf) * ((unsigned)s->bit_left / BUF_BITS) ;
  
      s->bit_left &= (BUF_BITS - 1) ;
  
  
  Casting s->bit_left to unsigned meant that the rounding is still towards
  
   inf ; yet the right side is now always positive (it transformed the
  
  arithmetic shift into a logical shift), so that s->buf_ptr will always
  
  be decremented (by about UINT_MAX / 8 unless n is huge) which leads to
  
  segfaults on further usage and is already undefined pointer arithmetic
  
  before that. This can be reproduced with the mpeg4 encoder with the
  
  AV_CODEC_FLAG2_NO_OUTPUT flag set.
  Furthermore, the earlier version as well as the new version share
  
  another bug : s->bit_left will be in the range of 0..(BUF_BITS - 1)
  
  afterwards, although the assumption throughout the other PutBitContext
  
  functions is that it is in the range of 1..BUF_BITS. This might lead to
  
  a shift by BUF_BITS in little-endian mode. This has been fixed, too.
  
  The new version is furthermore able to skip zero bits, too.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/put_bits.h

• I'm running a process in Java and am getting stuck when I wait for it to finish

  31 juillet 2020, par nottAbott

  I have a Java program that is supposed to make copies of segments of a video and then stitch them back together, using ffmpeg. My "snip" method, the one that makes the segment files, has a problem, it gets stuck when I call "process.waitfor()". When I take it out, the videos load partly, but cannot be accessed until I close the program. When I try to delete them, while the program is running, it says that they cannot be deleted because they are in use. Could anyone lead me in the right direction ? Here is the method :

  


  //snips out all the clips from the main video
public void snip() throws IOException, InterruptedException {
    
    for(int i = 0; i < snippets.size(); i++) {
        //Future reference: https://stackoverflow.com/questions/9885643/ffmpeg-executed-from-javas-processbuilder-does-not-return-under-windows-7/9885717#9885717
        //Example: ffmpeg -i 20sec.mp4 -ss 0:0:1 -to 0:0:5 -c copy foobar.mp4
        String newFile = "foobar" + String.valueOf(i) + ".mp4";
        ProcessBuilder processBuilder = new ProcessBuilder("ffmpeg", "-i", videoName, "-ss",
                snippets.get(i).getStartTime(), "-to", snippets.get(i).getEndTime(), newFile);
        
        //I tried this first and then added in the process/process.waitfor below
        //processBuilder.start();
        
        Process process = processBuilder.start();
        process.waitFor();
        
        System.out.println("Snip " + i + "\n");
        
        //add to the formatted list of files to be concat later
        if(i == snippets.size() - 1) {
            stitchFiles += newFile + "\"";
        }
        
        else {
            stitchFiles += newFile + "|";
        }
    }
}