PDA

View Full Version : How much does DivX shrink a file?


Aussie
18th April 2002, 02:41
I have been reading all about this DivX but can't find anything about how much it shrinks a file. Am I correct in assuming that DivX does to video what MP3 does to wav files? A music file can be shrunk up to 10 times the original size by using MP3. Does DivX do this to videos?

Thanks to everyone who replies.

tripnotik
18th April 2002, 03:11
Yes it does. For video, it's more like 150 times smaller than the original file.

gldblade
18th April 2002, 03:56
>For video, it's more like 150 times smaller than the original file.

I don't know about that. 150 seems a bit high to me, though I've never worked with uncompressed avi files, so I shouldn't know.

And it depends on if the original file has been compressed already.

Aussie
18th April 2002, 05:01
well, actually, at the moment I wish to do two things....

ONE: convert my mpg tv shows into DivX to shrink the size?

TWO: rip my DVD's to DivX

Should I even bother? :(

dragoman
18th April 2002, 05:14
Hi,

Well, aussie, it depends again on what you want to do.

Yes, you can reencode your mpg tv files to divx, but there's really not much point to this, as mpg 1 really doesn't take up that much more space than divx and you would take a quality hit if you do this.

Copying dvd's to divx is something I do, just purely as a backup action. Similar to archiving cd's on mp3 format, I back up my dvd's in divx format. If I am watching the movie on the computer, I use the divx rather than the dvd in order to guard against anything happening to the dvd.

Also it's kind of like a challenge....how small can I get a movie to get while it still looks awesome? I'll leave it to you to find that out....

dragoman

JimmyBarnes
18th April 2002, 08:43
Originally posted by Aussie
I have been reading all about this DivX but can't find anything about how much it shrinks a file. Am I correct in assuming that DivX does to video what MP3 does to wav files? A music file can be shrunk up to 10 times the original size by using MP3. Does DivX do this to videos?

When you say "video", what follows presumes you mean DVDs.

The VOB (Video OBject) files on a typical DVD might be 5-6 GB. Depending on the type of movie (widescreen, is it "dark" or "bright", how much "fast motion") you might convert it to a good quality DivX on 1 CD - 700 MB. The "good quality" is important because you can compress any movie however much you like but the results may not be watchable.

In the above example (5.5 GB to 700 MB) the compression ratio is about 8.

Many people choose to rip a DVD onto 2CDs to get higher quality so the compression achieved is less than it would be for a 1 CD rip.

JB

Aussie
18th April 2002, 09:35
Yes, you can reencode your mpg tv files to divx, but there's really not much point to this, as mpg 1 really doesn't take up that much more space than divx and you would take a quality hit if you do this
Well, that is the answer I was looking for. I honestly thought I could compress my tvshow.mpg (about 450 megs each)to fit 2 or 3 or even 4 episodes onto a 800MB CD (800 is currently the largest found here in Melbourne Australia) and then if anything happened to the "originals" I could just reburn them. I see that I might be able to do it but at a loss to the quality picture (which I am not willing to sacrifice)


When you say "video", what follows presumes you mean DVDs.
Yes, after my tv shows I wanted to back up my DVD's. The kids are ruining them. Basically, it looks like I need 2 DivX cd's to keep a good quality picture. Then again, it will take 2 Cd's if I use DVD2SVCD. I dont see the difference. I have a DVD player on my computer and a standalone DVD.

Thank you everyone for your input. After all I have read, plus everyones input here, I dont see a need for DivX except to transfer files over the net. I will keep my DVD2SVCD. Thanks again everyone, it was definatly a learning experience.

Cheers Mate

Aussie

theReal
18th April 2002, 19:59
Divx on two CD's should result in better quality than two SVCD's (you can keep the resolution higher) while a good one-CD divx should be about the same quality as a 2CD SVCD.
On the other hand, you can watch SVCD's with your DVD player, that's not bad either.

RadicalEd
18th April 2002, 21:06
Hi again aussie :)

Anyway, for the SVCD vs. DivX CD issue, the ideal situation is to do both, but thats only if you have enough time and cds.

Basically, SVCD is good for copying DVDs so that you can watch them on TV. If you're planning on using your computer to watch movies though, better to use DivX.

Aussie
18th April 2002, 23:12
Hey RadicalEd :) and thanks theReal. I guess the DivX debate has not let me down and has confused me even more...lol. I think I see in my future more reading and more studying up on this DivX. ugh.

JimmyBarnes
19th April 2002, 01:29
Originally posted by Aussie
I guess the DivX debate has not let me down and has confused me even more...lol. I think I see in my future more reading and more studying up on this DivX. ugh.

To make matters a little more complex :devil:, a new DivX codec (the software that does the compression) called DivX Pro 5 has arrived in the past month or so.

It seems to make possible 1 CD rips with an acceptable quality where the older DivX3 or 4 codecs would have required 2 CDs. I'm a 1 CD man myself and watch all my movies on a 68 cm TV.

JB

Nazgul
19th April 2002, 01:58
Originally posted by Aussie

Well, that is the answer I was looking for. I honestly thought I could compress my tvshow.mpg (about 450 megs each)to fit 2 or 3 or even 4 episodes onto a 800MB CD (800 is currently the largest found here in Melbourne Australia) and then if anything happened to the "originals" I could just reburn them. I see that I might be able to do it but at a loss to the quality picture (which I am not willing to sacrifice)

Well, depending on the quality and resolution of the original mpeg rip, divx might very well do what you'd want it to. I take vcd-level mpegs of tv shows and convert them to 320x240 Divx .avi's, and I'm currently doing it at a bitrate that allows 3 hour-long episodes(40-45 minutes each after the commercials get removed). Are they the same quality as the vcd? not quite, but they're close enough that on my regular 27" tv they look just fine. I suppose I could increase the bitrate so that I could only fit 2 on a CD, but I doubt it would give me enough quality to be worth it. Most of the quality loss seems to have been in the initial mpeg conversion.

SVCD would be a different story, but with Divx5Pro, you may still get great results. I took a 480x480 SVCD of a letterboxed widescreen tv show, and converted to 480x272 Divx5 at 600kbps and it looked pretty darn good. I even used the same bitrate at 640x368 and it still looked excellent, and that was before 5.01 came out and fixed up the psychovisual enhancements feature. At 600kbps I can fit 3 episodes on a CD just fine, especially if it was an 800MB cd(I try to work with the old-fashioned 650MB limit when possible). I'd be willing to wager that if you upped the bitrate to 900kbps for 2/disc, you might be quite satisfied.


Nazgul

dragoman
19th April 2002, 03:47
Hi

To clarify:

I never said it wasn't possible, just that you would get a small reduction in quality (compressing something twice is never a good idea).

I myself make VCD's out of divx files....if I have a movie I wish to watch on my big tv, I simply make a vcd, burn to 2 cd-rw's....watch, then recycle. I have the original movie on divx disc, so I can just erase the cdrw and watch another.

Takes a while, but hey....your comp doesn't sleep :)

Yes, the quality hit that is most noticeable is when you encode to mpeg-1 (oddly, vcd's made from dvd's or high-quality divx look great....guess it depends on the source.

dragoman

movmasty
19th April 2002, 09:05
-an uncompressed image is 3 bytes/pixel,"GKnot point" is 0.025B/pix, lets say 120 then,however max quality divx(quantizer 2)have 0.06,this is 50.

>a new DivX codec...DivX Pro 5 has arrived...It seems to make possible 1 CD rips with an acceptable quality where the older DivX3 would have required 2 CDs...
-imho divx3+nandub is still the best.many shadows in divx5.

-divx and mpg
>you can reencode your mpg tv files to divx...you would take a quality hit if you do this
-yes,recompression loss,but digital isnt like vhs,it could be very light,depends from each vid.

>The VOB (Video OBject) files on a typical DVD might be 5-6 GB...you might convert it to a good quality DivX on 1 CD - 700 MB...In the above example (5.5 GB to 700 MB) the compression ratio is about 8
-...8! well,then would have very much sense to convert also mpg1!
-typical DVD are 1 layer,2 layers are above 120min,and i would like to see a good dvd/divx of 140mins on one cd...
movies could be 90mins too,and they dont fill all the DVD,lets say a dvd movie has an average size of 4g
average size of a divx movie could be considered as 1g, 4 times then?
but a divx is 640x352 where the dvd is up to 720x576....
IME divx gets roughly 50/55% respect mpg1, and 40/45% respect mpg2 with "same recompressed quality"

-mpg2 are high bitrate-big files,so worth to convert them,and mpg1? IMO worths more!, since you pay what you get,to have the vcd quality needs less bytes,the high bitrate of mpg2 just lets you slightly more compression until eyes see artefacts.
Im used to do a bunch of mpg1-divx conversions.
-i read in the avisynth ref about temporal and spatial soften:"these filters can do miracles" yes!,cause if filtering can unbalance the high DVD quality,it can easy enhance the low vcd one,
try to use temp soften(1,7,11) spatialsoften(1,12,19) levels(10,1.00,248,0,255) on a noised vcd and you will see quality going up and size down.
-enlarging mpg1,i know that many people think that enlarging isnt any good,yet editing enlarging, using precise filters, is quite better than fast,on the fly,magnify.
IME you could get enhancements up to 150% resize,and at ~125% advantages are very noticeable.
i got good results using 416x320 with 4:3 mpg1,and 480x208/256 for movie formats,
note that watching at 640x480 you have 480/320=1.5, and 640/480=4/3,
these are very good ratios to resize full screen on the fly.
or if you prefer remain close to sources,352x264 for ntsc,and 384x288 with pal(DIVX ON MONITOR RES)
100/150 minutes of enhanced mpg1 on 700mb

> Are they the same quality as the vcd? not quite...
yes, they could be better, instead of "quality hit" you could get like a "photoshop retouching advantage"

theReal
19th April 2002, 13:03
movmasty has a point here: it depends on the quality of your vcd files if converting to divx (and applying filters before) is worth the effort. I got a really bad 2-CD Divx recently, it was encoded at a too low bitrate at 704x576 and it was about 2.5 hours long (the movie was "eyes wide shut"). A friend of mine had encoded it with Divx 4.12, Flaskmpeg and using some dumbass guide which said to leave the resolution at 704xNNN no matter what.
Of course the movie showed a lot of artefacts and ringing effects.

I decided to make a 1CD rip out of it, just to see what I can do. I resized it to 576x416, applied some smoothers before and after resizing, I re-encoded the CBR mp3@160kbit audio to VBR@112kbit and I encoded the credits with quantizer 32. The result was a movie that looks a little washed out (loss of quite some details), but it has much less artefacting and looks more pleasant to my eyes.

Had the 2CD rip been relatively good, I would have kept it as a 2 CD movie - but it looked so bad, I just had to do something about it. Now it's still not good, but at least it's 2.5 hours on only one CD!

Aussie
20th April 2002, 00:20
Well, what can I say :D I have decided to give it a try and see if I can fit two, then three, of my 450+MB shows onto one CD using DivX-5. I understand it takes a long time but using some of the great suggestions here I think I can do it.

Thank you everyone for your great advice. As always, I am not dissapointed by the professional advice given on this site. I will try it tonight (it is now Saturday morning here in AUstralia). Wish me luck :(

theReal
20th April 2002, 03:33
Good luck! :)

...btw. as a first hint for a good filter, I'd say try temporalsmoother(X) in avisynth. This filter alone can help very much with about any noisy video source. To set the strength X to something between 1 and 4 should be ok. If strength 1 is not enough but 2 is too strong already, you can set it to (X,1) which will apply it to a smaller radius.

The pre-processing filters in Divx5 pro are also quite good (and fast and easy to configure)

btw. I can't give you any "professional advice", I'm not a pro at all. Compared to those who program all the great video tools we are using, I'm only a slightly advanced beginner.

PeterTheMaster
20th April 2002, 23:44
@movmasty:
what filter do you mean with temp soften? temporalsmooter? but this one doesnt get 3 arguments!?

theReal
21st April 2002, 00:48
TemporalSoften(radius,luma_threshold,chroma_threshold)

PeterTheMaster
21st April 2002, 09:58
well, this doesnt belong here, but what exactly are these tresholds for? what happens if the chroma, luma values are higher/lower than them?

theReal
21st April 2002, 17:29
I have no clue... just try what these values are doing. For me, TemporalSmoother works better (maybe only because it's easier to set up and I had always used the wrong values for TemporalSoften ;) )

PeterTheMaster
21st April 2002, 18:08
i read a bit and can now answer my own question: these values are used to avoid the filter from mixing objects of different color with each other. they help determine which surrounding pixels should be including in calculating the average color. the higher they are the more pixel they allow.

movmasty
22nd April 2002, 07:47
radius is how many pixels blends together, the more,the stronger the effect

you can use higer values in chroma(+60%),so you can soften more chroma noise, and leave luma at its right value


regarding the compression of mpg4 respect mpg1,
Here (http://mpeg.telecomitalialab.com/)
are tests that show it is 70%

then an higer value respect our experiences.
but, isnt assured that we are wrong.