[FFmpeg-devel] [RFC] AVFilter Parser

[Vitor Sessak]

Michael Niedermayer wrote:
> On Tue, Mar 25, 2008 at 09:41:14PM +0100, Vitor Sessak wrote:
> [...]
>>>> 2- Let the ';' be interpreted like vrmsss's '*'
>>>> Advantages, Disadvantages: Same as (1)
>>> I don't think the choice of a symbol is important, it is the syntactic  
>>> mechanisms to combine streams which are important. I suppose we can  
>>> take everybody agrees on the key elements for that (functional or  
>>> sequential composition of filters --meaning outputs of the preceding  
>>> filter feed into inputs of the following one-- parallel or non- 
>>> sequential composition, rearrangement of streams via appropriate  
>>> namings, and feedback or looping). I don't think we are yet reached  
>>> the perfect way to express these, but we're close.
>> Maybe having both my ';' and your '*'. My ; is the last symbol in 
>> precedence, yours is the first. Mine operates in chains with no unlinked 
>>   pads. Yours operates in chains with one or more.
> 
> I think using () to override precedence is more natural than having 2
> identical operators but with different precedence.

I agree in general. But in this case, I see this operator as two 
different things: '*' means parallel processing, ';' means "end of a 
description block - beginning of an unrelated description block". Note 
also that if we extends the comma to link an arbitrary number of streams 
(including 0), it can replace the semi-colon (but I think it would make 
it more obfuscated).

> Also maybe see eval.c which contains a expression parser with +-*/^()...
> Not sure how usefull such a design would be for filters though ...

I'll have a look. But I made my suggestion based in clarity, not 
easiness to parse.

-Vitor