xvid codec compression under virtual dub

[limitless]

Hi I'm not sure if im posting in the right place because i just registered on this site so... please inform me if i should list the question elsewhere.

My problem is that Im trying to change the resolution of this avi file with virtualdub but in order to do that, I need to use the "Full process" mode in order to enable the filter "resize", after resizing and saved my new avi to a new file, i want to recompress the avi with xvid.

Under xvid video compression options it lets u select the "desired bitrate", i've set my desired video bitrate to 169 kbps but and audio to direct stream (original audio is 128kbps), but after compression my video becomes around 30 kbps only?? why isn't it 169kbps??

what did i do wrong?

Thanks in advance

EDIT: or tell me what other codecs besides the Xvid codec can compress decent videos, im so stuck !!

[Baldrick]

How do you check the bitrate after you encoded the video? how big is the file size and what is the video runtime?
What Encoding type are you using Single pass or 2-pass?
Does it looks like this:

[limitless]

yes i did exactly what u screened in that video, single pass, and the original file size is 1.2 gb with resolution 5xx (H) by 3xx (V) in 16:9 ratio, the original file size is 1.2gb because it was un-compressed. the runtime is 2 minutes and 5 seconds

and i check the video kbps by right clicking the avi, then go to properties.

[Scorpion King]

2min/5sec @ 169Kbps video / 128Kbps audio = 4.6MB filesize.

[jagabo]

and i check the video kbps by right clicking the avi, then go to properties.

That value is KBytes per second, not Kbits per second. Multiply by 8 to get kbits per second. Use Gspot or AVICodec to get more reliable results.

So if 30 KBytes per second is accurate your file is really around 240 kbps, not the expected 169. This makes more sense because Xvid has problems meeting very low bitrate requests.

[spanky123]

You're probably better off using Gordian Knot (which frameserves an avisynth to VirtualDubMod).
It's much easier than using straight VirtualDub and better imo (especially if you're new to this stuff).

[limitless]

yes scorpion but that's the file size of a compressed video.
and spanky whats an avisynth? sorry im really new to this stuff, and imo?

thanks jagabo, i think your formula really makes sense because i have gotten 37kB (i know its BYTE now) in the avi properties, that gives me 37 x 8 = 296 kb (bits) and 296 = almost exactly 128+169.

but the bitrate keeps changing itself during the compression, for example, i set the desired bitrate to 1224 in order to yield 169kB but the Xvid status always somehow changes it to 1015 and thus twist the kB/s to 146. I need to take a serious crack at this as i dont know why the actual result and my desired bitrate setting can differ so much??

and by the way, what are Gspot and AVICodec? are they compression codecs?

thanks again in advance guys

[jagabo]

AVISynth is a frameserving (the passing of video frames from one program to another without the intermediate step of saving the video to a file), editing, and filtering application. It's a very powerful tool but not so easy to use. AutoGK is a simplified front end that automatically uses AVISynth and VirtualDubMod to perform the work. It's easy for beginners.

I find that Xvid is usually pretty good at hitting the requested bitrate unless you are asking for very low or very high bitrates. On the other hand, I usually use Constant Quantizer (constant quality) encoding. I select the Quantizer (quality) I want and let the file come out to whatever size it does. With CBR or multipass VBR encoding you know how big your file will be but you don't really know the quality. With Constant Quantizer encoding you know what the quality will be but you don't know the file size.

Gspot and AVICodec are programs that analyse video files and give you lots of information about them. Things like what codecs are used, what bitrates, etc.

[Scorpion King]

yes scorpion but that's the file size of a compressed video.

When encoding video one either goes by the bitrate Kbps or Mbps, or the total filesize, which is a direct result of the bitrate. Stating an encode as KBps is plain out confusing. If you check your first post you will see it says, "i've set my desired video bitrate to 169 kbps." That is a long way from 1224Kbps. lol

So, 2minutes/5seconds @ 1224Kbps w/128Kbps audio = 20.3MB total filesize. If your filesize is near this value you have your bitrate that you set (1224Kbps).

Good luck.

[jagabo]

file size = bitrate * running time

Bitrate is the sum of both audio and video bitrates and is usually stated in kbits per second (kbps).

Running time is in seconds.

And of course the calculated file size is then in kbits, so divide by 8 to get kbytes.

The file will actually be a little bit bigger because of overhead of the container (MPG, AVI, etc).

[spanky123]

Well. The truth is you don't even really need to know a thing about Avisynth if you're going to use a good GUI like Gordian Knot, which makes the whole process extremely easy and straight forward. You just select how much you wanna crop, the filesize, the audio, and a couple other options/parameters and that's it. It's much easier IMO than using VirtualDub to do all that.

In short, an avisynth script is a type of text file with extension .avs that kind of has a list of commands that tell it's filters how to process the video.
For Example, here's a simple Avisynth script
AVISource("C:/My Videos/video1.avi")
Crop(10,2,10,2)
Resize(624,352)

If you want, and you're confident and familiar avisynth then you can make them yourself in notepad.
If your using Gordian Knot you don't need to worry bout making one yourself though, as Gordian Knot generates it for you.
It's worth knowing how to use avisynth, as it is compatible with most of the best encoding softwares out there (CCE, Procoder, TMPGenc, VirtualDubMod, Mencoder)

Hope I haven't confused you at all.