Coding in GK

[eliqush]

hi
when im recording something from tv
and the format wuold be MPEG uncompressed
for that i will code it to avi using GK
my question is how do i know how much to define the size of the file (mb)
someone told me that every minute should be 8 mb. is it right ? how it works?
10x always

[Baldrick]

It depends on the source, resolution, etc. so give us more information about source like the resolution and if it's interlaced.

But do you really need an exact size? If not use constant quality encoding and set the target quality. Try different values and see how it looks like. The output size will then depend on your source like lots of motions and details will mean bigger file size.

[eliqush]

the resolution is 512 * 384
and yes i need an exact size
so ou mean to mark - calculate avi file size
instead of - calculate averege bitrates?
or what?
10x

[jagabo]

file size = bitrate * running time

someone told me that every minute should be 8 mb.

That's rather arbitrary. What's the reason?

[manono]

My suggestion is to use AutoGK for the job as it can run single-pass quality encodes (where GK can't). Load the MPEG and set the width to 512 in the Advanced Settings (if that's what you want).

In the main screen use Target Quality (in percentage) set at the default 75%. That way you get the quality you define. If using the more complex Gordian Knot, your best bet is to run a compression test to help determine the best resolution and file size, before doing the actual encoding.

[eliqush]

ok so this is the actions that im doing:
http://tinypic.com/player.php?v=315hptw&s=4

let me know if im wrong
and how do i do a compression test?
thanks

[manono]

I'm not going to watch that blurry thing. The compression test is explained in the guides. Like this one:

http://www.rita.lt/guides/GKnot_DVDtoAVI.htm

Near the bottom. And I repeat my first suggestion of using AutoGK. If you don't know anything and have no intention of reading any of the many available guides so you can actually learn something, AutoGK will give you good results without you having to know anything at all.

[eliqush]

yes but autogk is doing only single pass
and someone here told me that single pass will bring low quality of coding
[?]

[jagabo]

Single pass constant quality encoding gives whatever quality you specify but you don't know what the file size will be. It's the flip side of bitrate based encoding where you know what the file size will be but you don't know the quality.

With constant quality encoding the encoder just compresses each frame to the quality you specify. It doesn't need to make two passes. With 2-pass VBR encoding the encoder has to first examine the video to find out what parts of it require more bitrate and which parts require less. Then during the second pass it allocates bits to maintain the best quality it can for the given average bitrate.

[manono]

yes but autogk is doing only single pass
and someone here told me that single pass will bring low quality of coding[?]

Someone told you wrong, unless that 'someone' was referring to single pass CBR encoding. AutoGK's 1-pass is very VBR.

Also, with single pass you get results much more quickly (one pass instead of 2), and it's guaranteed to look as good as the quality you set allows. If you let it complete, it looks very good, doesn't it?

[eliqush]

ok thanks for the comments.
i did compression test and those are the resaults:


my question is: how much mb should be each minutes so i can calculate
how to define the movie before the coding when the resolution is 512 * 384.
i prefer GK and not in Auto GK
because in Auto GK i can't add any filtere such as sharpen and null transform and its not good for me.
thats why i prefer GK
10x

[manono]

my question is: how much mb should be each minutes so i can calculate
how to define the movie before the coding when the resolution is 512 * 384.

There's no way to know unless you run the compress test for the whole movie. It has nothing to do with "MB per minute". Forget what your "friend" told you about that. However, once you get a compress test result you like, divide the total file size specified minus the audio size and a few MB for the muxing overhead by the number of minutes in the movie. In the one above you wound up with about 400%, even after AutoGK did all the adjusting it could. You want to aim for 65-80% or so, so you can lower the final size to something like a 5th the size you asked for. And that would be for a 720 width, so for a 512 width it should be even less (9th or 10th the original size specified). And if you want the final result to have a 512 width, you had best set it up for a 512 width originally. Here AutoGK adjusted the width upwards trying to get that percentage down.

...because in Auto GK i can't add any filtere such as sharpen and null transform and its not good for me.
thats why i prefer GK

Sharpen just makes it less compressible. Null transform? GK doesn't use that. That's a VDub term. Maybe you meant cropping? AutoGK will crop for you. You only have to give it the width, if it's important to you. Is this something else your "friend" recommended? I already pointed you to a guide where it explained the Gordian Knot compress test. If you can't figure out how to do that, you're surely not ready to use GKnot.

[jagabo]

how much mb should be each minutes so i can calculate
how to define the movie before the coding when the resolution is 512 * 384.

As was pointed out several times if you encode for a specific size you don't know what the quality will be. Some videos require lots of bitrate, some require less. Here is a post where I encoded two videos (same frame size, same frame rate, etc) at the same quality setting:

https://forum.videohelp.com/topic357646-60.html#1903520

One required 20 times more bitrate than the other (8000 vs 400). So there is no single bitrate that will give you "good" quality for all videos.

If you need a specific file size you should use 2-pass VBR encoding. But you'll have to live with whatever quality you get. If you don't need a specific file size you should use constant quality encoding.

Maybe this is what you're missing: If you encode a video with constant quality and it turns out at a particular average bitrate, then go back and encode the video again with a 2-pass VBR encoding at the same average bitrate, the two resulting videos will look almost the same.

[eliqush]

Maybe you meant cropping? AutoGK will crop for you. You only have to give it the width, if it's important to you.

how can i crop exactly? i didn't understand
what should i do in autogk to get it cropped

[manono]

how can i crop exactly? i didn't understand
what should i do in autogk to get it cropped

AutoGK crops away the black bars automatically. If you don't like the way it crops, or if it crops too much or too little, then you can make adjustments in the Hidden Options (CTRL/F9):

- Sometimes auto crop used with default parameters by AutoGK cannot totally remove black bars or removes too much of a movie material. In this case "Tune auto crop parameters" is very handy. Threshold defines how sensitive auto crop will be: the higher the value the more cropping will be done. To completely disable audio crop you can set threshold to 0. "Number of frames to examine" is useful parameter to change if movie is a mixture of full screen/wide screen shots, so by selecting different frames that auto crop examines you can improve cropping process. "Starting frame" can help auto crop in situation when you have a full screen logo as a part of widescreen movie, in which case autocrop might decide that the whole source is full screen. By selecting a different starting frames you force auto crop not to examine irrelevant starting movie sequence. "Force cropping" option allows you to crop additional pixels after autocrop operation (if you find that you need to always crop several more pixels you can use this option). If you disable autocrop with threshold 0 then "force cropping" option becomes fully manual crop. Remember always to check how movie looks like after you set new auto crop parameters using Preview function of AutoGK.

http://www.autogk.me.uk/modules.php?name=TutorialEN#6

[eliqush]

WOW nice 10x
i notice that even that gk make's too passes it does the job faster than autogk
4 example i coded movie of 25 minutes. and gk did the job within 2 passes in 20 minutes.
and when i did the same job with same parameters, autogk did it at 35 minutes.
and autogk makes only 1 pass
how is that?

[manono]

how is that?

Different settings. Maybe the GKnot resolution was less than the AutoGK resolution. Also, AutoGK runs a compression test which takes a little bit of time. And AutoGK makes the D2V file where in GK you make it yourself. Lots of reasons, including different XviD settings.