Why is .WMV bitrate so high?

GrandMasterKaja · #1 (**permalink**) 06-28-2005, 02:57 PM

CDs have a bitrate of 128kb/s right? So why is it that videos (usually .wmv files) have such a high bitrate? I cant even tell the difference between 128kb/s and 1000kb/s. Even when I tell it to do 44hz, 128kb/s as .wmv it forces the audio bitrate to match the video data rate.
I was under the impression that going beyond 312kb/s as far as audio bitrate was just unecessary.

Also, im wondering what happens if you take a 640x480 at 500kb/s file and jack it up to 720x480 at 1500kb/s? Now what would happen if I took that 720x480 1500 and brought it back down to 640x480 500 again? Would it look worse then the first 640x480 500?

Marc Peters · #2 (**permalink**) 06-30-2005, 07:19 AM

CDs have a bitrate of 128kb/s right?

I don't believe this to be true. CDs have uncompressed audio, so the "data" rate is quite high (1,411kbps).

Even when I tell it to do 44hz, 128kb/s as .wmv it forces the audio bitrate to match the video data rate.

You should not have to match the audio bitrate to match. Yes, an audio bitrate above 128kbps for the web is on the high side.

Also, im wondering what happens if you take a 640x480 at 500kb/s file and jack it up to 720x480 at 1500kb/s

The file size will go up. The quality at the native resolution will go down.

Now what would happen if I took that 720x480 1500 and brought it back down to 640x480 500 again? Would it look worse then the first 640x480 500?

Yes, because you would have re-encoded twice.

GrandMasterKaja · #3 (**permalink**) 07-03-2005, 11:50 AM

how come when you save songs from a cd onto your computer it's 128kbps?

Marc Peters · #4 (**permalink**) 07-03-2005, 11:51 AM

Because that's probably the mp3 bitrate you've chosen.

mrlipring · #5 (**permalink**) 07-03-2005, 03:50 PM

Originally Posted by GrandMasterKaja

CDs have a bitrate of 128kb/s right?

nope. CDs have a bitrate of 1411.2kbps. Ish.

So why is it that videos (usually .wmv files) have such a high bitrate? I cant even tell the difference between 128kb/s and 1000kb/s. Even when I tell it to do 44hz, 128kb/s as .wmv it forces the audio bitrate to match the video data rate.
I was under the impression that going beyond 312kb/s as far as audio bitrate was just unecessary.

depends on the codec. If it makes the audio bitrate match the video one, you're using the encoding app wrong wrong. most people can't tell the difference between CD and 192kbps mp3 on your average audio setup. Raise/lower that for whatever coded you like.

Also, im wondering what happens if you take a 640x480 at 500kb/s file and jack it up to 720x480 at 1500kb/s? Now what would happen if I took that 720x480 1500 and brought it back down to 640x480 500 again? Would it look worse then the first 640x480 500?

with every encoding step, you lose quality. you can't make shit into silver.

raising the bitrate and resolution will not make a difference. Indeed, resizing the resolution will lower the quality.

resizing back down to 640*480 would lower the quality yet again, probably making it considerably worse than the original unresized file.

really though, go and experiment. you can't break anything.

ask yourself why you're using wmv and not avi/xvid/mp3 though.

GrandMasterKaja · #6 (**permalink**) 07-04-2005, 07:08 AM

"ask yourself why you're using wmv and not avi/xvid/mp3 though."

I would but I cant figure out how to use .avi or xvid codecs. I cant make anything but a green bar going through a 4 second video playing at 100 times normal speed with Xvid and .avi I havent been able to figure out how to make decent looking 320x240. I can make decent looking 640x480 and up (would probably take a few tries). The problem there is the videos im editing are only a couple minutes long and they turn out to be in the 100MB+ region before they start looking good and I've seen others 30-40MB large that are just as good.

I have a problem though, premiere nor vegas dont read my already divx/mpeg-4 encoded files, it wont import it. I cant record anything except compressed 720x480 divx at a very low data rate so my original files look bad enough. So they look bad and I dont know why, maybe it's the program im using limiting my captures to such low quality. But now I gotta pour salt on it and go into windows movie maker (which is the only program that reads the files) and change them to .wmvs at 720x480 and a 2.1Mbps bitrate. Then I can edit them in premiere and THEN I have to figure out how to make a 320x240 bareable to watch.

Isnt there someway or some program I can use to capture video that looks as good as it does on normal TV?

mrlipring · #7 (**permalink**) 07-04-2005, 03:27 PM

well if it's analogue capping you want to be capping to full-d1, with the panasonic DV codec, or huffyuv.

I use IUvcr to cap.

edit your film, export to dv or whatever, then run it through virtualdub to compress to xvid.

if you want full-d1, then you'll be wanting ~1200kbps for the video. remember to deinterlace, crop any black borders, etc.

if you need to drop the bitrate, then you'll have to drop the resolution obviously. do a bicubic resize.

as always with xvid, do a 2-pass encode.