Why is WMV run time smaller than MPEG/MPEG2/MPEG4 run time??..

[numbfinger]

..hi again all, another newbie question from me..
Just curious, why is WMV file(s) smaller in file size than an MPEG/MPEG2/MPEG4??...
I've encoded some .avi files to WMV format, even with a high resolution and bitrate and the run time is less than half the time of the original files(.avi)...
Original .avi file: 15+ minutes(720x480 @ 29.9fps) --> WMV file: 6+ minutes(720x480 @ 5000 Mbps)..
While if i encode the same .avi file(s) to MPEG/MPEG2/MPEG4 formats, the new files retain the same amount of time as the orignal(.avi) files..
Thanks again for any inputs..

[Cornucopia]

If you're doing it right:

1. Runtime will always be EXACTLY the same for all formats.
2. CBR and VBR (AVERAGED, NOT MAX) will have similar filesizes with similar bitrates (given #1) (always varies a little).

This all depends on being able to use the right tools and know what settings mean and setting them to get your desired outcome.

If this didn't work consistently, there'd be no use for such things as bitrate calculators.

More homework...

Scott

[numbfinger]

If you're doing it right:

1. Runtime will always be EXACTLY the same for all formats.
2. CBR and VBR (AVERAGED, NOT MAX) will have similar filesizes with similar bitrates (given #1) (always varies a little).

This all depends on being able to use the right tools and know what settings mean and setting them to get your desired outcome.

If this didn't work consistently, there'd be no use for such things as bitrate calculators.

More homework...

Scott

Scott, thanks for the quick reply..
Well, i'm using Windows Media Encoder 9.0 as my conversion software.
On the Properties setting-Output, i matched everything the same as my original .avi file(s). I also selected the VBR option. I selected De-Interlace option. However, forgot to mention, everytime i did one of those encoding, at the end, there's always a msg which said "Found 3 erros". But when i played the just encoded WMV file, the time is much less than the original .avi file. Everything else looked & sounded fine.
What am i doing wrong? Am i missing a step or 2? Anyone familiar with Windows Media Encoder?..

[RabidDog]

DO you mean the file size is smaller or the clip is only half the time? The run time should stay the same whatever bitrate you use. You have probably dropped 50% of frames or speeded up the film or chopped it in Half.
avi file can refer to raw dv footage (lightly compresed) or mpeg4 avi (highly compressed)
---------------------------------------------------------------------------------------------------------
Compression hierarchy
RAW AVI(DV)-->
lightly compressed AVI=->
mepg2 (as in normal DVD)-->
mpeg4 avi (mov xvid divx nero 3ivx swf avc(?) )-->
Dirac droplet wavelet :P
---------------------------------------------------------------------------------------------------------

[numbfinger]

DO you mean the file size is smaller or the clip is only half the time? The run time should stay the same whatever bitrate you use. You have probably dropped 50% of frames or speeded up the film or chopped it in Half.
avi file can refer to raw dv footage (lightly compresed) or mpeg4 avi (highly compressed)
---------------------------------------------------------------------------------------------------------
Compression hierarchy
RAW AVI(DV)-->
lightly compressed AVI=->
mepg2 (as in normal DVD)-->
mpeg4 avi (mov xvid divx nero 3ivx swf avc(?) )-->
Dirac droplet wavelet :P
---------------------------------------------------------------------------------------------------------

RabidDog, thanks for your input.
I meant the runtime of the WMV clip is less than the .avi file(s). The file's size of course is now smaller than the raw/original file. That's what's bothering me, why the run-time doesn't match.
Yes, i know what .avi files are. My .avi files are from raw DV footage(recorded on a Mini-DV tape) and imported from camcorder thru firewire.
About me "dropping 50% of frames or speeded up the film or chopped it in Half.", i doubt i choose those. Although i'm not that familiar with WME settings.:P
Any other ideas?..

I'll try to show a pic later, of the "Errors" shown after the process had ended..

[Cornucopia]

Similar to MPEG "profiles and levels" there are certain combinations of frame sizes, bitrates, CBR vs. VBR, interlace, etc. that are valid in WMV, AND SOME THAT AREN'T.

I've had a few times where I would select certain combinations, make some changes, go back and reset other changes, and then WME would complain about a compressor NOT BEING AVAILABLE or some other message. However, if I wrote down exactly what I wanted to do, closed out the app and restarted it, loaded the source clip again, and simply ONE-BY-ONE made a change and clicked "apply", then made next change, blah blah blah, it would be FINE. Go figure. This is M$ we're talking about here...

Do me a favor, and take a short clip and load into and encode from WMM to WMV using one of the default output settings (like The WEB, DSL...). Does THIS work?
If so, it is very likely you choice of combination of output settings.
If not, you've got worse problems and may need to re-install something.

Scott

[numbfinger]

Similar to MPEG "profiles and levels" there are certain combinations of frame sizes, bitrates, CBR vs. VBR, interlace, etc. that are valid in WMV, AND SOME THAT AREN'T.

I've had a few times where I would select certain combinations, make some changes, go back and reset other changes, and then WME would complain about a compressor NOT BEING AVAILABLE or some other message. However, if I wrote down exactly what I wanted to do, closed out the app and restarted it, loaded the source clip again, and simply ONE-BY-ONE made a change and clicked "apply", then made next change, blah blah blah, it would be FINE. Go figure. This is M$ we're talking about here...

Do me a favor, and take a short clip and load into and encode from WMM to WMV using one of the default output settings (like The WEB, DSL...). Does THIS work?
If so, it is very likely you choice of combination of output settings.
If not, you've got worse problems and may need to re-install something.

Scott

Scott, thanks again for your reply...
Well, apparently my thread question is really a NEWBIE question, i must admit..:P
After going home yesterday and double checking, apparently i found out the video i tried to encode actually stopped about halfway thru the process. So, yes, the video got "chopped" in half, as RabidDog mentioned. That's why i only saw the run-time only lasts half the original file. And that's why i got the "Error msg".

With that out of the way, now i want to know:
1. Why and what i did wrong. If anyone is familiar with WME program, do you mind helping this newbie sort out the problem.
2. Is/are there quality differences between wmv and mpeg/mpeg2/mpeg4 formats??..Thanks again!!

As for the suggestion of encoding from WMM to wmv format, i'll try to look into that..thx

[Cornucopia]

Answers to Q's:
1. Don't know enough about your particular--System Hardware, Software Configurations, Source File history, Settings--to really know where the problem lies...
Troubleshoot by trying short sections and varying only one thing to rule out each possibility.

2. WMV is a proprietary variant of MPEG4, so it'll exhibit similar quality characteristics to MPEG4 (esp. Dixv/Xvid/MPG4-ASP). Assuming similar source, framesize, length, GOP settings, etc., WMV should be equivalent quality to DivX/Xvid/MPG4-ASP with similar bitrate. For some things it's better, for some it's worse (different optimization characteristics). It sometimes gets a bad rap because its 1. proprietary M$ and 2. used badly in the hands of newbies going for SMALLEST files.
Both of these (WMV vs. MPEG4-ASP) types are ~2x more efficient than MPEG2 at equivalent bitrates.
Looking at it 2 ways: Same bitrate = Better quality (than MPEG2), Lower bitrate = Same quality.

Scott

[numbfinger]

Answers to Q's:
1. Don't know enough about your particular--System Hardware, Software Configurations, Source File history, Settings--to really know where the problem lies...
Troubleshoot by trying short sections and varying only one thing to rule out each possibility.

2. WMV is a proprietary variant of MPEG4, so it'll exhibit similar quality characteristics to MPEG4 (esp. Dixv/Xvid/MPG4-ASP). Assuming similar source, framesize, length, GOP settings, etc., WMV should be equivalent quality to DivX/Xvid/MPG4-ASP with similar bitrate. For some things it's better, for some it's worse (different optimization characteristics). It sometimes gets a bad rap because its 1. proprietary M$ and 2. used badly in the hands of newbies going for SMALLEST files.
Both of these (WMV vs. MPEG4-ASP) types are ~2x more efficient than MPEG2 at equivalent bitrates.
Looking at it 2 ways: Same bitrate = Better quality (than MPEG2), Lower bitrate = Same quality.

Scott

Scott, thanks again for the reply.
Well to comment on your 2 points:
1. My source files are .avi format and i can encode them to MPEG format(with a different program) with no problem. However, i'm having difficulties with using WME. Running on Windows XP, P4 w/ 1GB of RAM.

2. When you said "Both of these (WMV vs. MPEG4-ASP) types are ~2x more efficient than MPEG2 at equivalent bitrates.", what do you mean by "efficient"??..Also what do you mean by "used badly in the hands of newbies going for SMALLEST files."??..

Thanks again for your explanation between WMV and MPEG4.

[Cornucopia]

As has been said before, there are about 51 varieties of video codecs being used within the AVI container. Some are much harder than others to decode/re-encode without frame corruption or sync problems.

Have you tried converting 1st to uncompressed (or losslessly or DV) AVI with LPCM audio? This should have less trouble being decoded, so the WMV encoder would have an easier time parsing the file for the encode. I'd suggest Virtualdub for this job.

The more efficient a codec is, the more it can retain quality using the same remaining bits.
Let's say you have a pilllow with lots of fluff. If you press down hard, you can squeeze (compress) most of the air out. It will be alot smaller, but will still be the same pillow.
But if it isn't small enough, you could use one of those "vaccuum" devices that suck the air out of a package. Putting the pillow in a package and sucking the air out will make the pillow much smaller still. That's "more efficient". And it's still a pillow.
But what if you were able to align the fluff in the pillow so they all lined up horizontally end-to-end and straightened out the bumps and then used the vaccuum device...the pillow might be even a third of the original vaccuumed size. So, Efficient = compresses more smartly.
Now the only thing about "shrinking" the pillow is that when you try to restore it, it doesn't quite have it's usual fluffiness--one of the losses incurred in the compression process.

re: newbies,
There are supposed to be certain settings used for certain kinds of sources or in certain situations, and with those who understand the nuances, one can often get the outcome desired. Newbies, OTOH, often start with something that is so-so quality to begin with, and then apply the wrong settings (meant for a different target application) and blindly go for the lowest filesize that they shortsightedly imagine they can afford. That's compounding error upon error upon error upon error. The result gets broadcast on the internet in droves, and then WMV gets a "reputation", similar to (old) RealMedia quality.
In reality, WMV is scalable just like any other general purpose codec, so it has bitrates where quality is pretty mediocre and then good and then acceptable and then great.

Good luck,

Scott