[FFmpeg-devel] [PATCH] Stream specifier enhancement

[Marton Balint]

On Thu, 15 Oct 2015, Bodecs Bela wrote:

[...]

>>> My enhancement does not alter the current behaviour in any way.
>>
>> Are you sure? What if somebody matched a semicolon, or a string which 
>> contained a semicolon in a metadata value? E.g.: m:timecode:00:00:00:00
>>

This question still stands. Will the m:timecode:00:00:00:00 specifier work 
the same way as it did after your patch? I think it will not.

[...]

> I do not understand this. My patch only gives an opportunity to use 
> multiple specifiers in the same expression, it is not mandatory to use 
> it. The patch does not affect any existing command line in any way.

I don't agree, I think your patch changes existing behaviour and the 
proposed syntax limits future extensibility.

> I also accept your concern about the future, but double semicilon always 
> will works for optional parameters. But may I ask: would it be better to 
> introduce a "special character" for separating specifiers in the same 
> expression?

IMHO yes. You also have to know from the start that you are dealing with a 
complex specifier, in order not to break existing simple specifiers.

> I accept it if you suggest one. I only need the functionality to be able 
> to give more criteria to select a stream as opposed to current 
> oppurtunities. I am not stuck to my suggestion.
> Anyway, You may see my enhancement as you get many optional parameters 
> for the existing type, metadata and program_id specifiers. :)

It can be anything if it does not change existing behaviour, a complex 
specifier can be split to basic specifiers without worrying about the 
syntax of the basic specifier and if there is a well defined rule for 
escaping special characters. Also if it is readable to the user, that is a 
plus.

The exact solution can be a bit about personal taste as well, but maybe 
something like

(specifier)(specifier)

or

+specifier+specifier

can work and is readable. Knowing that you are dealing with a complex 
expression also means that the special characters separating the basic 
specifiers needs escaping, I guess av_get_token can be used to get the 
proper unescaped basic specifiers when parsing the complex one.

Regards,
Marton