[FFmpeg-user] Changing the crop filter's output width over time?

[Gyan Doshi]

On 26-04-2020 10:51 am, John Hawkinson wrote:
> I wanted to execute zoom-and-pan out over a few seconds by parametrizing the width and height of the crop filter via sendcmd (the result of which would then be handed to a scale filter), and when I try to do this, I get errors that I don't understand.
>
> When I use:
>
>    sendcmd=c='0-1 crop w 1146+t*(1920-1146), crop h 1080'
>
> I get:
>
>    Error when evaluating the expression '1146+t*(1920-1146)'
>
> When I use
>
>    sendcmd=c='0-1 crop w 1146+T*(1920-1146), crop h 1080'
>
> I get:
>
>    Unknown function in 'T*(1920-1146)'
>    Error when evaluating the expression '1146+T*(1920-1146)'
>
> Neither of these seem to make sense to me. The crop filter docs indicate it takes the parameter 't', and the general eval api docs refer to 'T'. I'm not sure which (or both?) applies, but both fail in odd ways.
>
> Same problem with a simpler exmpression like '1146+T'.
>
> What am I doing wrong? Console output below.

The temporal parameters t, n and pos are only applicable for x and y 
expressions. At present, the only way to vary w and h over time is by 
sending commands with varying constants for w/h. Not very convenient, I 
know. Open a ticket if you want an enhancement for the crop filter.

Gyan