[FFmpeg-devel] [PATCH 2/3] Add section describing the filtergraph.

Stefano Sabatini stefano.sabatini-lala
Sat Nov 13 10:35:59 CET 2010

On date Friday 2010-11-12 20:42:31 -0500, Mike Scheutzow encoded:
> Stefano Sabatini wrote:
> >On date Friday 2010-11-12 15:14:15 -0500, Mike Scheutzow encoded:
> >>Michael Niedermayer wrote:
> >>>On Fri, Nov 12, 2010 at 01:32:55AM +0100, Stefano Sabatini wrote:
> >>>>---
> >>>>doc/filters.texi |   86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>>>1 files changed, 86 insertions(+), 0 deletions(-)
> >[...]
> >>Stefano:
> >>
> >>Why do you want to have two such similar concepts: a FILTERCHAIN and
> >>a FILTERGRAPH? Having both adds complexity and will increase user
> >>confusion. I don't understand the benefit this gives us.
> >[...] It's not something which I did invented myself, I just took
> >the
> >implemented syntax and described it. Also what do you want to remove?
> >
> >A graph is not a list, so for describing it you need to specify each
> >connected sequence (aka filterchain), the current syntax seems quite
> >convenient to me, the alternative would be to label every link in each
> >filternode.
> If this is meant to answer my first question, I didn't understand
> your response.
> Let me try a more concrete question:
> Example 1. -vf "hflip, vflip"
> Example 2. -vf "hflip; vflip"
> Is there a functional difference between example 1 and example 2?
> From reading your filter description, I believe the output of both
> examples
> is exactly the same.

In a filterchain:
|If an output pad is not labelled, it is linked by default to the first
|non-labelled input pad of the next filter in the filterchain.

Example 1 is a filterchain, so output pad of hflip (unlabelled), is
linked to the first unlabelled input pad of the following filternode
in the filterchain, that is of vflip.
This is equivalent to:
hflip[L], [L]vflip

or to:
hflip[L]; [L]vflip

but not to:
hflip; vflip

since hflip and vflip belong to different filterchains so they are not
automatically linked.

If you have suggestions for improving the description they're welcome.
FFmpeg = Fancy Fantastic Marvellous Portentous Emblematic Game

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