[FFmpeg-devel] [PATCH] vf_scale: Detecting changes of incoming frame properties and dinamically evaluate width and height expressions

Bodecs Bela bodecsb at vivanet.hu
Tue Jan 19 23:51:33 CET 2016

2016.01.19. 19:00 keltezéssel, Bodecs Bela írta:
> 2016.01.19. 16:53 keltezéssel, Carl Eugen Hoyos írta:
>> Bodecs Bela <bodecsb <at> vivanet.hu> writes:
>>> To retain the current behaviour and not to break any
>>> earlier app, a new config parameter has been introduced.
>> Is the current behaviour useful or do you consider it a bug?
> First I thought that it was a bug, but I borrowed an idea from 
> vf_overlay filter, where there is a very same config parameter causing 
> a very similar behaviour distinction on expression evaluation.
> I will soon post a patch to vf_overlay where there was really a bug in 
> this behaviour.
So I think that the current behaviour is useful in some cases: when you 
use expression but you want to have fixed sized output even when the 
input frame size is changing.
(If anybody wonder why does somebody use expression instead of fix value 
in this case? Well, if you write a script to handle many different sized 
input file.)
For the new behaviour, I gave a usage scenario in my other post. And I 
know that the new behaviour is not important for most of the users.
Additionally, most user do not care either behaviour because dynamically 
sized video content is very rare.
This is the reason why I introduced the eval-mode option. So the user 
may decide which behaviour is good for him/her.
So my patch has no risk for any current user but some of them will be 
happy because of the new feature.

> bb
>> Carl Eugen
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