[FFmpeg-soc] expand filter (alternative to pad syntax)

[vmrsss]

Hi everybody

	I attach an improved version of vf_pad.c, thoroughly tested, with a  
few questions for you.

(1)
On 15 May 2008, at 10:30, Víctor Paesa wrote:
> Try sscanf(arg,"%d:%d:%d:%d:%255[^:]:%255[^:]:%d",&a,&b,&c,&d,e,f,&g);

I am having a problem with inputs like

	pad=::::16/9:16

(which should mean "expand to a 16/9 frame mod 16"), because sscanf  
can't find the %d in between the ::, and so the conversion stops.  
Ideally the form above should be allowed, lest one needs to ask users  
to type in clumsy forms with default values as in:

	pad=-1:-1:-1:-1:16/9:16

(which is what the code currently requires). Is there to get sscanf do  
it? I don't think so. One alternative is to use sscanf to read args  
one ":" at a time, as I currently do for two of the parameters which  
can take different forms (aspect and color).

(2) Following up on the above, would a form like

	pad=w=...:h=...:x=...:y=...:a=...:r=...:c=....

be desirable? It'd allow to omit parameters and list them in any  
order, but for filters with few parameters might be a cumbersome  
overkill. Eg

	scale=624:368 against scale=w=624:h=368

(3) I have added the possibility of specifying a color for the  
padding. The structure which lists the colors is taken from  
vf_drawbox.c. If people like the idea, that can easily be factored out  
in some avfilter_common file.

(4) The aspect parameter doesn't work as it should for files with SAR  
different from 1. It's easy to fix, only that the sar information  
seems unavailable at the filter configuration stage (see the code); I  
expect Vitor wll be able to help on this one.

(5) I have not resolved the issue of removing memcpy. There is only  
one call to memcpy in the code; to get rid of it is likely to require  
some significant change to the avfilter API, that will have to involve  
Vitor. In these circumstances, I wonder whether it would make sense to  
commit the code to SOC anyway, and then remove the one call to memcpy  
when we'll know how. (Observe that this situation is common to several  
filters.)

Regards,
-vmrsss

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