[FFmpeg-user] Using the "select" filter

Tim Nicholson tim.nicholson at bbc.co.uk
Wed Nov 23 11:19:15 CET 2011

On 22/11/11 20:30, Clément Bœsch wrote:
> On Fri, Nov 18, 2011 at 11:06:12AM +0000, Tim Nicholson wrote:
>> On 17/11/11 19:10, Clément Bœsch wrote:
>>> On Thu, Nov 17, 2011 at 08:09:40PM +0100, Clément Bœsch wrote:


>>> Erh. I meant:
>>>     ffmpeg -i in.mp4 -vf select='eq(pict_type,\I)',showinfo -f ...
>> Actually you meant:-
>> ffmpeg -i in.mp4 -vf select='eq(pict_type\,I)', showinfo -f ...
> Yes, without the space before showinfo since there is no surrounding
> quotes.

AGGGH, its so much easier with quotes....

> The documentation is a bit inconsistent I agree, but I think the examples
> should have the '\' in it: it's more obvious when the failure occurs on
> the '\' instead of the comma: "why does it fails on the comma? I don't see
> why I need to escape it...", while in case of the an extra escape the most
> common thought is something like "herp derp yet another shell escaping
> issue i need to double escape, remove escape, ..." which is more likely to
> lead to a solution.

I think it doesn't help that all examples that give the full command 
line and include quotes around the filtergraph are simple syntax ones 
where the quotes aren't actually needed... A more complex example shown 
in both forms would probably help.

Also some more complex examples showing the development of a graph from 
a simple filter to chains, to chains with branches would, I think, make 
the whole thing more accessible to newcomers. Filter syntax questions do 
seem to come up quite often.

> Also note the shell escaping varies between shells (I know tcsh has for
> instance a totally insane way of escaping).
> I think examples with the full command line should include the " ", or at
> least a command that obviously work out of the box.
> On the other hand, if it's just for the -vf part, I don't think the
> surrounding quotes should appear: it is obvious you have to send that part
> of the command line "verbatim" to FFmpeg, so deal with your shell.

I think I agree with both of those

> Of course the documentation could be improved, but I don't feel like doing
> it :)

> If you want to discuss such topic, you are welcome on ffmpeg-devel.

When I have some space I might propose something there, and even submit 
a patch. I have a growing "cheat sheet" of examples I use myself.

> PS: sorry for the late reply.

no problems


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