video rescaling

[Patrick Welche]

On Sun, Jun 07, 2020 at 04:05:36PM +0100, Ian Davidson wrote:
> Many formats like multiples of 4 - so maybe a width of 401 could throw it. 
> Try 404.

Thanks! Even (n%2=0) works!

Patrick

> 
> On 07/06/2020 15:29, Patrick Welche wrote:
> > 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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