KVCD: Encode with Constant Bitrate, Load .AVS File, Change Resolution?

Edlund · #1 09-14-2003, 03:45 PM

This is a posting that I think will be either "Another newbie post" or "Something we should think about".

Here is basically the discovery:
I did a few tests and the results were - When you encode with constant bitrate you can load a .avs file and change the resolution to whatever you want. The filesize remains the same. It doesn't depend on the resolution or the filters you are using. These settings affect only the encoding time.
My conclusion : For me personally the prediction times are over. I can now easily get a file with the desired filesize and great quality that can fit on one cd. What prevented me from posting this some time before was the fear that maybe you will not trust me or that you really must use constant quality. I know that the KVCD matrix is not the "rate control mode" that you are using but the quantize matrix. And this matrix can be used for templates using constant bitrate. I can't hold such big secret anymore and think that it will be for the good of all of us if what I found out is of any use.

P.S. Of course I am absolutely aware that maybe you have found this before and I'm not saying anything new and basically I am writing bullshit

Jellygoose · #2 09-14-2003, 03:57 PM

Hi Edlund...

Don't be afraid to write any discoveries you made, we're all thankful for new techniques that have to be tested and nobody will make fun of you here.

Of course constant bitrate is "constant" so that it will not change whatever resolution you pick. however higher resolutions also need a higher bitrate to look good. A clip with high action will probably look good with standard VCD resoluton 352x240/288 and a CBR of 1150kb/sec. However I doubt that the very same clip will look as good at 704x480/576 at 1150kb/sec since the higher resolution will require a higher bitrate too. Anyway I gotta admit I haven't tried it yet.

jorel · #3 09-14-2003, 03:58 PM

Quote:

Originally Posted by Edlund

"Something we should think about".

Here is basically the discovery:
I did a few tests and the results were - When you encode with constant bitrate you can load a .avs file and change the resolution to whatever you want. The filesize remains the same. It doesn't depend on the resolution or the filters you are using. These settings affect only the encoding time.

The filesize remains the same???

seems (is) impossible

Edlund · #4 09-14-2003, 04:05 PM

Yes, the filesize remains the same. The filters from avisynth don't affect it. Try yourself.

Edlund · #5 09-14-2003, 04:09 PM

Quote:

Originally Posted by Jellygoose

A clip with high action will probably look good with standard VCD resoluton 352x240/288 and a CBR of 1150kb/sec. However I doubt that the very same clip will look as good at 704x480/576 at 1150kb/sec since the higher resolution will require a higher bitrate too. Anyway I gotta admit I haven't tried it yet.

Hmm, yes, you're right. That's why I wonder if there's a filter for this that canbe used and if more "sharpness" in the script will help solving this problem.

Dialhot · #6 09-14-2003, 04:12 PM

Quote:

Originally Posted by jorel

The filesize remains the same???

seems (is) impossible

That's the definition of Constant Bitrate Jorel !

With a CBR of 1150 Kb/s every second of you movie will take you EXACTLY 1150 bytes. Whatever you encode (big noisy image of 720*480 or small blurry image of 352*28

, you will use the same space. This is not a scoop

.

The problem that Edlund didn't see yet, is that for it will use the same bitrate for a very slow motion scene (even a static picture !) or for a heavy action sequence. And then the problems will happen : while you lost A LOT of space in static part of the movie, you don't have enought for action ones. The last become blocky and pixelized in order to stay in the constant bitrate you have fixed.

That is why we use VBR : to adapt the amount of space used following the actoin of the scene.

Edlund, what you found is what it's used in VCD since a long time. And we all know the "quality" of VCD

. SVCD drop the CBR encoding mode to have a better quality. And KVCD follow this path.

Don't be sad Edlund but the last part of you first post is unfortunally all true

Edlund · #7 09-14-2003, 04:17 PM

I know that this is nothing new but the avisynth filters are changing the situation. With them you use the "lost space in static part of the movie" for increasing the quality.

Dialhot · #8 09-14-2003, 04:19 PM

Quote:

Originally Posted by Edlund

Hmm, yes, you're right. That's why I wonder if there's a filter for this that canbe used and if more "sharpness" in the script will help solving this problem.

Nothing you can do will avoid the problem appearing with short of birate : blocks.

The more you sharpen, the more birate you need (and you don't have as you are in CBR mode -> birate is constant), and the bigger the blocks are.

jorel · #9 09-14-2003, 04:22 PM

" (big noisy image of 720*480 or small blurry image of 352*28

"

ok Phil,now i "see"!
means...horrible?!?!?

Edlund · #10 09-14-2003, 04:22 PM

Quote:

Originally Posted by Dialhot

Don't be sad Edlund but the last part of you first post is unfortunally all true

Yes, I know that I'm not the first to think about this but the facts are : I put 90 minutes movie on one cd with super quality, used your avi script at 704x480. The only defects are the high motion scenes, their imperfection can be seen when you look at the TV from 50cm. (or if you have a very big screen

Dialhot · #11 09-14-2003, 04:24 PM

Quote:

Originally Posted by Edlund

I know that this is nothing new but the avisynth filters are changing the situation. With them you use the "lost space in static part of the movie" for increasing the quality.

Yes, you do that in VBR mode, not in CBR mode : the space you save in static scene, you will use it latter in moving ones.
Ibn CBR you can save anything : each second of movie eats the same piece of the cake. You can save a nuts to use it with the next piece. You have to eat all the piece even if you do not need it before to go to the next one.

Just try this : encode a movie in 480*480 using CQMatic and Calcumatic, as always. Let say that Calcumatic give you an average of 1000 Kb/s.
After the encoding, do the same test with a constant bitrate of 1000 Kbs.
Both mpg will be the exact same lenght but look at them... you will see immediatly why we use VBR and not CBR.

Dialhot · #12 09-14-2003, 04:30 PM

Quote:

Originally Posted by Edlund

The only defects are the high motion scenes, their imperfection can be seen when you look at the TV from 50cm. (or if you have a very big screen

No need of a bif screen, you can eve see them on your PC screen. It seems that you just not very sensitive to the blocks default and you are lucky in one way

.

I wish to be so "blind" to these defaults. Unfortunally I'm not

(perhaps you don't know but I used to be part of the quality tests of MPEG2 algorythm when it was still in the labs. So my eye is well trained to all its artifacts).

Dialhot · #13 09-14-2003, 04:34 PM

Quote:

Originally Posted by jorel

ok Phil,now i "see"!
means...horrible?!?!?

Horrible, perhaps not (it depend on the movie. Can be everything from horrible to not so bad).

But as Edlund told, he does a movie in "super quality". Let say that with KVCD we are looking for "excellent" quality.

Edlund · #14 09-14-2003, 04:37 PM

Quote:

Originally Posted by Dialhot

Just try this : encode a movie in 480*480 using CQMatic and Calcumatic, as always. Let say that Calcumatic give you an average of 1000 Kb/s.
After the encoding, do the same test with a constant bitrate of 1000 Kbs.
Both mpg will be the exact same lenght but look at them... you will see immediatly why we use VBR and not CBR.

Yes, but I can encode in 720x576 with my method and only once. I don't need to care about the prediction methods and encode the movie once and it gets too big, or it gets too little and not so good quality. Not to mention all this hanging around this and other forums until my eyes get hurt. This drove me mad sometimes and I often thought "Why all this efforts when I can just sit on the not so comfortable chair in front of my pc for an hour or two and watch".

jorel · #15 09-14-2003, 04:39 PM

"Can be everything from horrible to not so bad"

"not so bad" is a girl with wonderful body and ugly face!
"horrible" is a girl.....horrible..."everything"!

totonho03 · #16 09-14-2003, 04:46 PM

Quote:

"not so bad" is a girl with wonderful body and ugly face!
"horrible" is a girl.....horrible..."everything"!

Trubufu?

jorel · #17 09-14-2003, 04:50 PM

Quote:

Originally Posted by totonho03

Quote:

"not so bad" is a girl with wonderful body and ugly face!
"horrible" is a girl.....horrible..."everything"!

Trubufu?

yeah!

Dialhot · #18 09-14-2003, 04:50 PM

Quote:

Originally Posted by Edlund

Yes, but I can encode in 720x576 with my method and only once. I don't need to care about the prediction methods and encode the movie once and it gets too big, or it gets too little and not so good quality.

But what I want tell to you is that your "one shot 720*576" encoding has a quality far below the one you would obtain by making all the "file size prediction" process.

Time is not a priority there. Quality is. That is the difference between your point and the one I try to (friendly) stand for.

But the goal of all of this is to be happy with the result we have. If you are with a CBR encoded movie, just do it. And enjoy

jorel · #19 09-14-2003, 04:53 PM

yes Edlund,
but try the kvcd way...you never back to standards!

Edlund · #20 09-14-2003, 04:54 PM

Quote:

Originally Posted by Dialhot

Nothing you can do will avoid the problem appearing with short of birate : blocks.

The more you sharpen, the more birate you need (and you don't have as you are in CBR mode -> birate is constant), and the bigger the blocks are.

So I will have to do a test with a 2 hours movie and maybe I'll have to stick with CQ for bigger movies but use my method for movies up to 90 minutes.