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• fftools/cmdutils: Use avfilter_pad_count() for AVFilter's number of pads

  12 August 2021, by Andreas Rheinhardt

  fftools/cmdutils: Use avfilter_pad_count() for AVFilter's number of pads
  Besides being nicer code this also has the advantage of not making
  
  assumptions about the internal implementation: While it is documented
  
  that the AVFilter.inputs and AVFilter.outputs arrays are terminated
  
  by a zeroed sentinel, one is not allowed to infer that one can just
  
  check avfilter_pad_get_name(padarray, i) to see whether one has reached
  
  the sentinel:
  
  It could be that the pointer to the string is contained
  
  in a different structure than AVFilterPad that needs to be accessed
  
  first: return pad->struct->string.
  
  It could be that for small strings an internal buffer in
  
  AVFilterPad is used (to avoid a relocation) whereas for longer strings
  
  an external string is used; this is useful to avoid relocations:
  
  return pad->string_ptr ? pad->string_ptr : pad->interal_string
  
  Or it could be that the name has a default value:
  
  return pad->name ? pad->name : "default"
  
  (This actually made sense for us because the name of most of our
  
  AVFilterPads is just "default"; doing so would save lots of relocations.)
  The only thing one is allowed to infer from the existence of the
  
  sentinel is that one is allowed to use avfilter_pad_count() to get
  
  the number of pads. Therefore it is used.
  Reviewed-by: Nicolas George <george@nsup.org>
  
  Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] fftools/cmdutils.c

• FFmpeg av_guess_format returns NULL

  12 September 2014, by Kage

  I’m following the example code here: http://cekirdek.pardus.org.tr/ ismail/ffmpeg-docs/output-example_8c-source.html

  My code is as follows:

  fmt = av_guess_format(NULL, filename, NULL);
  
  if (!fmt) {
  
          LOGE(1,"Could not deduce output format from file extension: using MPEG.\n");
  
          fmt = av_guess_format("mp4", NULL, NULL);
  
  }
  
      if (!fmt) {
  
          LOGE(1, "Could not find suitable output format\n");
  
          exit(1);
  
  }

  The two times that I call av_guess_format, it is returning NULL both times.
  I am calling both av_register_all() and avcodec_register_all() beforehand.

  Any ideas as to why this is returning NULL?

  Thanks in advance.

• avutil/opt: Avoid av_strdup(NULL)

  25 March 2024, by Andreas Rheinhardt

  avutil/opt: Avoid av_strdup(NULL)
  It is not documented to be safe and in any case it is nonsense:
  
  Currently av_strdup(NULL) returns NULL and in order to distinguish
  
  this from a genuine allocation failure, opt_copy_elem()
  
  checked afterwards whether src was actually NULL. But then one
  
  can simply check in advance whether one should call av_strdup()
  
  at all.
  
  set_string() was even worse and returned ENOMEM in case the value
  
  to be duplicated is NULL; this only worked because
  
  av_opt_set_defaults2() does not check the return value at all
  
  (given that it can't propagate it).
  These two places account for 389114 of 390356 av_strdup(NULL)
  
  calls during one FATE run.
  Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavutil/opt.c