[FFmpeg-devel] [PATCH] Change default behaviour of scale filter from 'progressive' to 'auto'
mark at mdsh.com
Wed Apr 4 23:13:39 CEST 2012
On 02/04/2012 22:11, Mark Himsley wrote:
> I'll demonstrate in another email (when I get my act together) the
> issues you can get if you scale progressive material with an interlaced
> scaler (it's not criticism of the scaler!).
Got my act together. I throw this out as observation and as a discussion
point, and not as criticism.
I've knocked up a couple of images that demonstrate the "problem" with
doing interlaced scaling with progressive media. If I recall I can't
attach image files to this list so I've put them onto a web page.
The first image, http://mdsh.com/ffmpeg/lines.png, is made up of some
over-sharp diagonal lines.
I converted that to a video file, which looks ok.
ffmpeg -loop 1 -r 25 -i lines.png -vframes 100 -vcodec libx264 -crf 21
-top 1 -an lines-1920.mov
I scaled that to an SD video file in interlaced mode
ffmpeg -i lines-1920.mov -vf
scale=704:576:interl=1,pad=720:576:8:0:black -aspect 16:9 -vcodec
libx264 -crf 21 -top 1 -an lines-720.mov
And exported that to a picture again.
ffmpeg -i lines-720.mov -vframes 1 lines-720.png
You should see from the exported image
http://mdsh.com/ffmpeg/lines-720.png that the diagonal lines are not
diagonal. That demonstrates how PSNR figures of progressive material can
be knackered by interlaced scaling.
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