video rescaling

[Patrick Welche]

On Sun, Jun 07, 2020 at 02:53:05PM +0100, Ian Davidson wrote:
> 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?

A typo in the testing :-/ Thank you!

The question about ratios still stands though:

video/x-raw,width=400,height=300,pixel-aspect-ratio=1/1  -> 400x300
video/x-raw,width=401,height=300,pixel-aspect-ratio=1/1  -> FAIL

(original = 560x320)

How do you know what is allowed?  (500x320 OK, 501x320 fail)

Cheers,

Patrick

> 
> 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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> > gstreamer-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
> 
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