Quality Percentage?

[hodney]

Hi

I am backing up my films for use on an Archos pmp. I generally use the single pass quality percentage option as file size isn't as important as quality for me.

I just tried backing up a long film using 3 different settings as a trial. 40% quality gave me an Xvid file with a video data rate of 58kbps and was 448MB. 50% quality gave me a data rate of 70kbps and was 540MB. Lastly 60% quality gave me a data rate of 84% an was 644MB.

My question is that I am wondering if the data rate is linked to the % quality? For example, If I backed up a different film using 50% quality would that be encoded using 70kbps as well? Also, what is classed as a "good" data rate for an Xvid file?

Lastly, all 3 movies looked good at a resolution of 480 pixels wide. The 40% quality Xvid was worse at full screen but I don't want to play them at full screen anyway. I am wondering how low can I put the % quality to still get a good Xvid?

Thanks for your advice

[Wolfman]

the higher the quality setting the higher the datarate will be.
quality settings will result in different data rates for diferent movies.I would say that 1400 is a good datarate.I personally think xvid and divx are fairly equal at those sorts of bitrate. however by squishing the resolution down to 480 you can save a lot of datarate so maybe 800-1000. The only way to tell about how low is to judge with your own eyes. cartoons will compress a lot better than other films as there is far less detail in them (generally)

[manono]

Hi-

My question is that I am wondering if the data rate is linked to the % quality?

For the same movie, yes. For different movies, not really. Different movies compress differently. You'll get very different bitrates when doing Saving Private Ryan and Sin City for the same Quality Percentage, to name a couple of movies off the top of my head, one compressing badly, and the other very well.

I am wondering how low can I put the % quality to still get a good Xvid?

That depends mainly on the resolution and the movie. There are no hard and fast rules about these kinds of things.

I guess I just said the same things as did Wolfman. :)

[hodney]

Thanks for the information. I will experiment a little more.

Is there anyway of setting the bitrate before encoding? Or is a quality % a better way of ensuring good quality?

[manono]

Since file size and bitrate are directly correlated, when you do a traditional 2-pass encode for a specific file size, that's how you encode for a specific bitrate. But no, you can't choose the bitrate in AutoGK.

[stax76]

I am wondering how low can I put the % quality to still get a good Xvid?

For XviD encoding I recommend quantizer 3 if you decode with post processing, without post processing quantizer 2.5.

After AGK configured the codec you can use VirtualDub to see what quantizer what AGK percentage is since XviD stores in the registry and thus remembers always what parameters where used the last time.

Please note that generally for ASP it's recommend to use post processing, for AVC it's not used since it has in-loop deblocking. For me every post processor other than DivX produced poor quality so I use XviD to encode and DivX to decode, maybe I'm doing something wrong, there is not much information available on the topic.

I am wondering how low can I put the % quality to still get a good Xvid?

That depends mainly on the resolution and the movie. There are no hard and fast rules about these kinds of things.

How is the resolution involved in quality mode? So far I was able to encode anything with quantizer 3, that should map always close to 60% quality which also worked so far for any source

With 60% quality I mean calculated from q2 using the file size.

[manono]

I guess that last remark was directed to me. He's making these things for his Archos. It has a small screen. So, a lower percentage, when viewed on the small screen, will still give him a decent quality. Although it's nothing I'd want to view on my HDTV, he said that even 40% quality gave him good results. Therefore, the smaller the display, the lower you can let the resolution and percentage go. I've never watched a movie on one of these things. I don't know that I'd like to.

But thinking about it some more, I see your point, and I said it wrong, and shouldn't have mentioned resolution. I should have said something more to the effect that quality is subjective, and he'll have to decide for himself what the lower limit of percentage is good for him and the Archos. Thanks for the correction.

[hodney]

Thanks again for all your help. I have decided to encode at 60% for now as that gave good quality at 480 resolution.

I have one more question for you if thats OK.

The Archos screen is 16x9 aspect ratio (480x272 pixels). I have some 4x3 material that I would like to encode so it fills the full screen. What is the best way of doing this? Is it possible to encode it so it stretches to fill the full screen? If not, is it possible (and easy) to crop some of the top and bottom of the picture to make it widescreen?

Thanks for your advice

[stax76]

The PMP template in StaxRip detects *all* image related settings automatically for this display size.

[hodney]

Thanks Stax - I will have a look at your program.

However, I am getting used to using AutoGK now. Does anyone know how I can encode 4x3 into 16x9 using AutoGK?

Cheers

[stax76]

However, I am getting used to using AutoGK now. Does anyone know how I can encode 4x3 into 16x9 using AutoGK?

I would say AutoGK can't help you much with this problem but you can try to get this working, search a solution and create another topic if everything else fails.