[FFmpeg-user] Using expressions in "FADE" filter

[Shlomo Morosow]

Sorry email was sent before complete:

https://www.ffmpeg.org/ffmpeg-utils.html#Expression-Evaluation

I regularly use this in many filters and it works just as expected, it's
just that I ran into an issue with the fade filter.

Thanks,
Shlomo

On Thu, Apr 30, 2015 at 12:31 PM, Shlomo Morosow <smorosow at jemedia.org>
wrote:

> Thanks Moritz,
> The reason I need to use mathematical values is because I'd like to make a
> preset command to fade out the last second of any given video and since the
> fade filter needs to be instructed on when to begin in relation to the
> start of the video I need to be able to tell it to start at duration minus
> one second.
>
> Regarding the documentation on using expressions in filters, this can be
> found in the the text-expansion section of the ffmpeg filters documentation:
>
> https://www.ffmpeg.org/ffmpeg-utils.html#Expression-Evaluation
>
>
> To which can be applied the the expressions-evaluation found in the ffmpeg
> expression-evaluation documentation:
>
>
>
> On Thu, Apr 30, 2015 at 3:50 AM, Moritz Barsnick <barsnick at gmx.net> wrote:
>
>> On Wed, Apr 29, 2015 at 17:57:43 -0400, Shlomo Morosow wrote:
>> > I need the ability to input mathematical values for setting the start
>> time
>> > (st)  on the "fade" filter, I've attempted to use an expression and this
>> > particular filter does not seem to work with expressions, nor simple
>> math
>> > as "10*1".
>>
>> As far as I can tell, you are right in saying that this filter (or at
>> least the "st" argument) does not support expressions.
>>
>> For "st", it also doesn't make much sense. Expressions are used not for
>> convenient calculation, but rather for expressing something which
>> changes over the course of a media stream, i.e. depending on frame
>> count, timestamp or the likes. "st" can only ever express a constant
>> value.
>>
>> If you need to do math, you can let your interpreter (on Unix: the
>> shell) do the math for you. I'm not sure how to do this on Windows (and
>> usually avoid it, even professionally). ;-)
>>
>> > ffmpeg.exe -y -ss "0:00:20" -t "0:00:10" -i input.avi -filter_complex
>> > "fade=out:st=%{expr\\\: (10-1)}:d=1" -f dvd -target ntsc-dvd -r 29.97
>> > -aspect 4:3 -b:v 4500k -mbd rd -trellis 1 -flags +mv0 -cmp 0 -subcmp 2
>> -b:a
>> > 128k output.vob
>>
>> Where is it documented that an expression is expressed as such?
>>
>> Moritz
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>>
>
>
>
> --
>
> *Shlomo Morosow*
>
> *The Living Archive · Archive Manager*
>
> 781 East New York Ave, Brooklyn, NY 11203
> *t *718.774.1800 x1450 *c *347.693.7196
>



-- 

*Shlomo Morosow*

*The Living Archive · Archive Manager*

781 East New York Ave, Brooklyn, NY 11203
*t *718.774.1800 x1450 *c *347.693.7196