video rescaling

[Ian Davidson]

Is the use of

pixel-aspect-ration

in your examples (with 'n' at the end) a typo in your posting or a typo 
in your testing?

On 07/06/2020 14:34, Patrick Welche wrote:
> On Sat, Jun 06, 2020 at 12:54:25PM -0400, Nicolas Dufresne wrote:
>> Le sam. 6 juin 2020 11 h 15, Patrick Welche <prlw1 at cam.ac.uk> a écrit :
>>
>>> Given a sample video, e.g.,
>>> http://techslides.com/demos/sample-videos/small.ogv
>>> and following the videoscale documentation,
>>>
>>> gst-launch-1.0 -e \
>>> filesrc location=small.ogv ! decodebin ! video/x-raw ! videoconvert \
>>> ! videoscale ! video/x-raw,width=50 ! ximagesink
>>>
>>> does exactly what one expects. If I channel the output to a file
>>>
>>> gst-launch-1.0 -e \
>>> filesrc location=small.ogv ! decodebin ! video/x-raw ! videoconvert \
>>> ! videoscale ! video/x-raw,width=50 ! x264enc ! filesink location=out.mp4
>>>
>> Unlike ximagesink, x264enc supports non square pixels. As it's zero copy,
>> videoscale will prefer scaling the pixel-aspect-ratio field instead.
>>
>> Set pixel-aspect-ratio=1/1 in your filter if you want to force scaling.
> Thanks! It seems there is more to it though...
>
>  From the videoscale documentation, I had the impression that I
> could throw any old height & width in and hope that what came out
> was whatever is specified in the filter after the videoscale element,
> and if it is ridiculous, I may get a black border (add-borders=true),
> but it would still be the desired size.
>
>
> AFAICT that sample small.ogv is 560x320. If I try            I get
>
> video/x-raw,width=400,height=300,pixel-aspect-ration=1/1    525x300
> video/x-raw,height=300,width=400,pixel-aspect-ration=1/1    525x300
> video/x-raw,height=300,width=400                            525x300
> video/x-raw,height=300                                      525x300
>
> which suggests height wins, and 560*300/320 = 525
>
> If I try
>
> video/x-raw,height=301
>
> I get "Can not initialize x264 encoder"
>
> Does this mean videoscale only scales integer ratios of height, or
> is there more to it?
>
>
> Cheers,
>
> Patrick
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