[FFmpeg-devel] [PATCH] documentation: Fix several documentation bugs in trac ticket #2413

[littlebat]

On Sat, 6 Apr 2013 01:59:19 +0200
Stefano Sabatini <stefasab at gmail.com> wrote:

> On date Friday 2013-04-05 21:58:09 +0800, littlebat encoded:
> > On Fri, 5 Apr 2013 12:40:40 +0200
> > Stefano Sabatini <stefasab at gmail.com> wrote:
> [...] 
> > /opt/ffmpeggit/bin/ffmpeg -i in.avi -vf \
> >   "movie=logo.png [logo]; [out] [logo] overlay [in_0]" out.avi
> > 
> > It seems the input video stream linked [out] automatically, and the
> > command line works well! I suppose these two special links "[in]"
> > and "[out]" have been dropped in the current ffmpeg, or they don't
> > function properly if they are still designed as special labels. 
> 
> Interesting:
> ffmpeg -i INPUT -vf  "movie=ffmpeg-logo.png [logo]; [foo][logo]
> overlay [bar]" -y OUTPUT
> 
> Looks like if there is an unconnected filter input it is connected to
> the default filter output, and the unconnected filter output is
> connected to the default filter input. This was the result of some
> relatively recent work on -filter_complex, but seems more like an
> (undocumented) glitch rather than a feature.
> 
> The equivalent command fails with ffplay:
> ffplay INPUT -vf  "movie=ffmpeg-logo.png [logo]; [foo][logo] overlay
> [bar]" [...]
> Output pad "default" with type video of the filter instance
> "ffplay_buffer" of buffer not connected to any destination

I see, "[in]" and "[out]" are still designed as the special labels in
the entire ffmpeg system. Using them is not harmful, but, lacking 
them, some times, will cause problem, as your ffplay example above. My
understanding is ok? 

>diff --git a/doc/filters.texi b/doc/filters.texi
>index 483d8a1..773657f 100644
>--- a/doc/filters.texi
>+++ b/doc/filters.texi
>@@ -5,8 +5,8 @@ Filtering in FFmpeg is enabled through the libavfilter
>library. 
> In libavfilter, it is possible for filters to have multiple inputs and
> multiple outputs.
>-To illustrate the sorts of things that are possible, we can
>-use a complex filtergraph. For example, the following one:
>+To illustrate the sorts of things that are possible, we consider
>+the following filtergraph.

I found you still reserve the sentense "
 In libavfilter, it is possible for filters to have multiple inputs and
 multiple outputs.", but, the example here is just one video stream in
and out, so, is this sentense a harmful influence on your
example? Is it better to delete this redundant sentense? Or, add some
thing to indicate this? for example, like below:
 In libavfilter, it is possible for filters to have multiple inputs and
 multiple outputs.
 To illustrate the sorts of things that are possible, we consider
 the following filtergraph(this filtergraph has only one input and
output stream).