Avidemux: questions quantisation vs quantisation like source etc.

[MovingParts]

Hello,

h.264 movies obviously don't play well on a PowerPC Mac, so I tried mpeg4 ASP (xvid or ff).

First there is "quantisation type h.263 or mpeg". I get confused with the codec and the format, what would "Mpeg quantisation be there". You don't need to answer that, if it is to stupid.

My more important question is.
Quantisation seems to be something like motion or picture estimation, right?

What is recommended?
What would be the fastest?

I guess constant bitrate is the less hazzlesome, right?

[jagabo]

The quantization matrix controls what frequencies are deprecated in the DCT domain. The mpeg matrix gives sharper results but requires higher bitrate. The h.263 matrix gives less sharp results but does better at lower bitrates.

[MovingParts]

OK, I guess for old machines that can't handle video well it would be good to choose mpeg and then set a high bitrate, right.

[El Heggunte]

It depends on "how old" the machine is, and also on the intended video resolution and frame rate.
Just as an example, my 1.5GHz Pentium-4 can play DivX/Xvid @ 1280x960 @ 30fps without issues.

[MovingParts]

Hm, I know that there are several videos I can play, but know as I think of it, it would be good I could find the threshhold by trial and error. But I don't think it is a good idea converting several videos myself, because I have to few knowledge and control over it and would probably get lost in trying the alternative settings.

Is there a page were I can maybe download sample files for different resolutions, framerates and codecs.

I know though, that usually xvid is no problem, it gets hard when something h.264 is involved, I can play some with low resolution.

It is an ibook G4 1,33GHz (PowerPC, not Intel!) the last model from 2005, but that doesn't say anything, because as wwe all know Win and Mac machines are hardly comparable.

So far as I have come now, it seems lowering the resolution does have a massive effect on the playability, less so than any sort of bitrate (while we're talking mpeg4 part2), I didn't make much progress with h.264. Although I know it is possible.

Edit: would lowering the fps from 50fps PAL (source) to 25fps do something good?

[jagabo]

Maybe you can find a copy of the old Divx-Xvid Test CD. It had many files on it with different frame sizes and bitrates encoded with Divx and Xvid.

http://club.myce.com/f7/divx-xvid-test-cd-v2-0-a-202146/

All the links are dead but you might be able to find it elsewhere.

[MovingParts]

OK, googled quickly, but couldn't find it, no problem, I will have to turn later to it anyway.

A last question on quantisation. When I read "constant quantisation" and "quantisation like Source" I asssume, that the second would not alter the media, as much as (or completely) the first, right?

[jagabo]

A last question on quantisation. When I read "constant quantisation" and "quantisation like Source" I asssume, that the second would not alter the media, as much as (or completely) the first, right?

No. A lower quantizer than the source will retain more image quality. But will result in a higher bitrate (all else being equal).

[MovingParts]

sorry, if I sound dumb, but just to be sure, for quality picking constant quantisation is best?

[jagabo]

It doesn't matter whether you use target quantizer or target bitrate encoding, neither is better or worse. The difference is: with target quantizer encoding you know what the quality will be (relative to the source) but you don't know the file size. With bitrate based encoding you know what the file size will be but you don't know what the quality will be. When the two methods deliver the same bitrate (file size) the quality is pretty much the same.

If you have bitrate restrictions you should use bitrate based encoding because quantizer based encoding in Xvid doesn't limit bitrate peaks.

[MovingParts]

I was asked to upload a log file and was given a link, where I could temporarily upload it unfortunaely, when I go through my recent threads I can't find the thread where I was asked for it. Can someone name me the upload page, so I can search that in my browser history and find the thread via that one?

[jagabo]

You can click on your name to the left of any of your posts and select "view forum posts". That will give you a list of all your posts.

[MovingParts]

Thanks, I know, that is what I did. I first searched all threds started by myself and then all posts, but couldn't find it. Then I posted, if someone could help me find it. BUt I have maken a very stupid mistake! It was in the HAndbrake-Forum, not in this. This explains, why I couldn't find it here. sorry.