Very noob questions about bitrate in XviD video encoding

vbimport

#1

Hi :slight_smile:

I have some veeery noob :o:o questions about bitrate.

In these days I’m doing some tests with AviDemux. I was able to convert a full DVD in avi, but there are a lot of options in codec settings (I’m using XviD), and for most of them I have no idea which one select :o

btw, if I understood correctly, to make an avi with acceptable quality it is necessary to set the proper bitrate, or resulting quality will be ugly.

Again, if I understood correctly, the bitrate to choose for the avi is related in some way to the bitrate of the original movie, so if the DVD has a high bitrate I can select a not too high bitrate for the avi, so it is possible to make a smaller file with an acceptable quality.

But if the original DVD has a low bitrate, using a too low bitrate on the avi will make quality ugly.

So, there is a way to determine the bitrate of original movie?

There is a thumb rule about how to choose the correct bitrate for the avi based on the bitrate of the original DVD so that resulting quality will be acceptable?

Is it totally nonsense to use the same bitrate of the original DVD to make the avi?

TIA :flower:


#2

DVD movies use mpeg2, and the bitrates for mpeg2 do not correspond 1:1 when converting to xvid, so don’t try to use the same bitrate. Many commercial dvd movies will be 4500kbps-6000kbps, and you probably won’t need anything over 1800kbps for the xvid version.

If your original movie has a lot of action, you’ll probably need to increase bitrate in the xvid conversion to maintain quality. A more static film can get by with less. So the nature of the film has to be considered as well as numbers.

Your main concerns are the length of the move in time, the resolution you want and your target size. Those are what you should concentrate on when determining your xvid bitrate when converting from commercially made dvds. There are a few bitrate calculators floating around, like this one at videohelp.com: http://www.videohelp.com/tools/VideoHelp_Bitrate_calculator
and this one at Divx: http://labs.divx.com/BitrateCalc

Within AviDemux, you can set the encoding mode and use two pass encode with either a target size, or an average bitrate you want to hit. But frankly, worrying about this sort of thing to get the very smallest size file while maintaining quality can drive you crazy…er, crazier. :slight_smile:


#3

Just adding to Kerry56’s excellent post/reply…Generally using two pass variable bitrate will give better results than single pass constant bitrate…It of course makes sense to do your own testing, and determine what settings best suit your needs(eyes)…You might also consider what you’ll be playing back the AVI’s…PC or DVD player?..Not all players support it, and not all AVIs are created equal…
Here’s one BRcalc I use.
http://www.videohelp.com/tools/VideoCalc
http://forum.videohelp.com/topic352457.html


#4

If filesize is not a concern you can also use the ‘Constant Quantitiser’ and XviD will automatically adjust the bit rate for consistent quality. Again, YMMV so try it and see what’s best for you…


#5

Thanks all for your answers :slight_smile:

I’ll do some tests (and of course I’ll do a mess :p)

I’m starting to like AviDemux :iagree:


#6

After starting out with various of the all-in-one tools, I’m now very much a proponent of doing video conversions manually, step-by-step. There is an excellent DVD 2 Xvid guide here which is where I started learning about bitrates. I tend to use AviSynth as a frameserver rather than VFAPI Reader and do any cropping/resizing with AviSynth so that I can use the Fast Recompress mode in VirtualdubMod.

I’ve had excellent results using the suggested 1500kbps bitrate for fullscreen (720x576, 4:3 or 16:9 anamorphic) resolution video (action film) with no noticeable artefacting when viewed on a 42" widescreen LCD TV. The bitrate can be proportionally decreased with the framesize, so at 720x436 (anamorphic 2.35:1) 1200kbps gives similar results.

The other thing to consider is the matrix used. The H263 matrix is generally recommended for best results with lower bitrates (e.g. to fit 1 CD) while the mpeg matrix is preferred for higher bitrates. I’ve yet to start experimenting with custom matrices, but it’s only a matter of time :wink:

Best of luck with your experimentation.

Slainte

midders


#7

Thanks for your answer midders :slight_smile:

[QUOTE=midders;2463287]
The other thing to consider is the matrix used. The H263 matrix is generally recommended for best results with lower bitrates (e.g. to fit 1 CD) while the mpeg matrix is preferred for higher bitrates.[/QUOTE]

Too bad my standalone is not able to play movies encoded with H263 matrix. I already tried it, so I’m forced to use the mpeg matrix always :doh: