[Libav-user] What exactly is AVFilterPad and AVFilterInOut within libavfilter?

Nicolas George nicolas.george at normalesup.org
Sat Aug 10 13:00:41 CEST 2013

Le duodi 12 thermidor, an CCXXI, sunswang a écrit :
> I am currently trying to figure out how to resolve the "output pad .... no
> source found" error from a modification of the ffmpeg audio filter example
> because I am using a filter that requires 2 or more inputs.

Please do not trim error messages.

> However, I am having trouble understanding exactly what "AVFilterPad",

AVFilterPad is used to describe an input or output of a filter: its type,
its name, pointers to functions used to handle incoming or outgoing frames
and a few more technical details. It is part of the filter.

> "AVFilterInOut" are in playing a roll towards filtering.

AVFilterInOut is mostly a way of encoding the information "the 4th input of
the concat filter": a pointer to the filter context, and the index of the
designated input or output. Plus a next pointer to build a linked list, and
possibly a name if the structure comes from parsing a graph description.

For example, if you parse a graph that says "[0:a] [ex] amerge", you get
two AVFilterInOut for the input:
- one pointing to the context for amerge, index #0, name "0:a";
- one pointing to the context for amerge, index #1, name "ex";
and one AVFilterInOut for the output:
- pointing to the context for amerge, index #0 (it has only one output),
  name NULL.


  Nicolas George
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