[FFmpeg-user] Docs, filtering introduction example

[Michael Ludwig]

Carl Eugen Hoyos schrieb am 04.04.2013 um 20:30 (+0000):
> Michael Ludwig <milu71 <at> gmx.de> writes:

> > (Okay, no error with N-51511-g599866f from 2013-04-01, 
> > but not the desired result either.)
> 
> This is ticket #2413, a patch is currently discussed 
> on ffmpeg-devel.
> Further improvements are of course welcome!

Okay, I agree with the #2413 author.
Will see if I can improve the docs.

By the way, the reason the original example on the doc page
is wrong is because (a) it crops the bottom half of the
image which isn't supposed to appear in the output at all,
and (b) it uses the cropped part as the main input for the
overlay, so the resulting output ends up too small.

The #2413 author posted a correct example, at the end of
the ticket description, where he uses a fifo filter, which
could be removed, I think (although I don't understand its
purpose), and which has been removed recently.

http://ffmpeg.org/trac/ffmpeg/ticket/2413

[FFmpeg-devel] [PATCH] doc: remove mention of fifo filter in the introduction.
http://ffmpeg.org/pipermail/ffmpeg-devel/2012-December/135982.html

I think the following examples are clear, in decreasing
order of explicitness:

-vf "[in] split [S1][S2]; [S2] crop=iw:ih/2:0:0, vflip [Mir]; [S1][Mir] overlay=0:H/2 [out]"
-vf "[in] split [Whole], crop=iw:ih/2:0:0, vflip [Mir]; [Whole][Mir] overlay=0:H/2 [out]"
-vf "[in] split [Whole], crop=iw:ih/2:0:0, vflip, [Whole] overlay=0:H/2 [out]"

Michael