[FFmpeg-devel] [RFC] AVFilter Parser

[Vitor Sessak]

Michael Niedermayer wrote:
> On Tue, Mar 25, 2008 at 10:57:34PM +0100, Vitor Sessak wrote:
>> 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).
> 
> how do you plan to do parallel processing of filter chains then?
> 
> example:
> (scale,crop,brightness)*(contrast,rotate,flip)*(gray,scale,rotate,saturation) , picinpic*nop , picinpic
> 
> vs.
> 
> scale*contract*gray , crop*rotate*scale , brightness*flip*rotate, nop*nop*saturation , picinpic*nop , picinpic
> 
> I think its clear which is more readable ...

Yes. But this is about implementing parenthesis or not, not about the 
semi-colon. Another example

(in1) --> split        --> scale --> crop ----------> picinPic -->(out1)
             \--> split --> vflip --> rotate --> picInpic--/
                    \-----> gray  --> scale ------/

(in2) --> crop --> vflip --> (out2)

(in3) --> scale --> crop --> (out3)

(in1) split,nop*split, (scale,crop)*(vflip,rotate)*(gray,scale) , 
picinpic*nop , picinpic (out1);
(in2) crop, vflip (out2);
(in3) scale,crop (out3);

vs

(split,nop*split, (scale,crop)*(vflip,rotate)*(gray,scale) , 
picinpic*nop , picinpic)*(crop,vflip)*(scale,crop)

This example could be worse, I was just too lazy to draw more 
complicated graphs for the other inputs.

-Vitor