Resizing in avidemux

donfrenchiano · 17th May 2011, 14:00

Ive been using gordian knot and autogk to encode dvds to avis for years and recently i began looking at avidemux. I was wondering how AutoGK determines how it resizes a video. autogk picks a resolution for you automatically and its different every time. In avidemux you have to specify it manually as far as i can tell. Is there some way to determine what would be the best resolution to resize a video to based on size, bitrate or something else?

LoRd_MuldeR · 17th May 2011, 16:21

There is no such thing as a "best" resolution, except for the original video's "native" resolution!

Generally it is highly recommended to not resize at all. If you do resize, you should know why you need a resize. And then you also know what your target resolution is.

If you do not have a good reason to resize, then simply do not resize

Be aware: Some applications use "bits per pixel" (aka "bpp") as a metric to predict the quality of the re-encoded video.

So maybe (I don't know, I just speculate) AutoGK will lower the resolution based on the target average bitrate (target file size) until a certain minimum "bits per pixel" value has been reached.

It should be obvious that using "bits per pixel" as a quality indicator is complete nonsense, because it completely leaves out the "complexity" or "compressibility" of the individual video!

Having said that, in extreme cases, such as ultra-low bitrate encodes, it may indeed make sense to downsize the video prior to encoding. Generally that's not the case though.

detmek · 18th May 2011, 14:49

I didn't use AutoGK since 2007. but AFAIK it does compressability test using CQ2 to calculate resolution.

17th May 2011, 14:00	#1 \| Link
donfrenchiano Registered User Join Date: Aug 2010 Posts: 35	Resizing in avidemux Ive been using gordian knot and autogk to encode dvds to avis for years and recently i began looking at avidemux. I was wondering how AutoGK determines how it resizes a video. autogk picks a resolution for you automatically and its different every time. In avidemux you have to specify it manually as far as i can tell. Is there some way to determine what would be the best resolution to resize a video to based on size, bitrate or something else?

17th May 2011, 16:21	#2 \| Link
LoRd_MuldeR Software Developer Join Date: Jun 2005 Location: Last House on Slunk Street Posts: 13,244	There is no such thing as a "best" resolution, except for the original video's "native" resolution! Generally it is highly recommended to not resize at all. If you do resize, you should know why you need a resize. And then you also know what your target resolution is. If you do not have a good reason to resize, then simply do not resize Be aware: Some applications use "bits per pixel" (aka "bpp") as a metric to predict the quality of the re-encoded video. So maybe (I don't know, I just speculate) AutoGK will lower the resolution based on the target average bitrate (target file size) until a certain minimum "bits per pixel" value has been reached. It should be obvious that using "bits per pixel" as a quality indicator is complete nonsense, because it completely leaves out the "complexity" or "compressibility" of the individual video! Having said that, in extreme cases, such as ultra-low bitrate encodes, it may indeed make sense to downsize the video prior to encoding. Generally that's not the case though. __________________ Go to https://standforukraine.com/ to find legitimate Ukrainian Charities 🇺🇦✊ Last edited by LoRd_MuldeR; 17th May 2011 at 16:26.

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18th May 2011, 14:49	#3 \| Link
detmek Registered User Join Date: Aug 2009 Posts: 463	I didn't use AutoGK since 2007. but AFAIK it does compressability test using CQ2 to calculate resolution.