Nandub / SBC Encoding
Everybody's talking about it, the new Smart Bitrate Control (SBC)
method of encoding DivX movies. The program used to do this is
called Nandub and was written by a fellow who goes by the handle_nn_!
Nandub is basically a 'hacked' version of VirtualDub (but hacked
with permission). It controls DivX encoding frame by frame! Doom9
was the first to show everyone how to use Nandub. If you haven't
seen Doom's webiste yet I think you should check it out because,
well, he's such a cool bloke! You can go to it by clicking Here!
To the untrained eye it looks like Nandub produces higher
quality at a smaller filesize! For example, you all know
that a movie encoded with the Fast Motion codec at 6000kbps will
always produce a final movie worse looking than a Low Motion
encoded at 3000kbps! So you think lovely I'll use Low Motion and
it will be half the size and twice the quality, right? Wrong!
If you compare the 6000kbps movie to the 3000kbps movie you will
find that the filesize of the 3000kbps is actually twice that
of the 6000kbps movie! The same is true for Nandub or Windows
Media Encoder 8 or even MM4 encoding (such as MakeFilm or AVIRevolution).
When you compare one of these clips to the same clip encoded by
any normal DivX codec the Nandub or MM4 clip will always be larger
or the same quality. The power of these programs is only their
ability to make the most efficient use of all the space available.
To do this Nandub uses the best possible method a 2-pass Variable
Bitrate (VBR) encoding scheme!
Nandub certainly has the potential to produce the best results
above any other method so far. But unfortunately for all its millions
of controls most of them do very little to produce better quality.
I have found that only two or three options are responsible for
a significant quality control. I will highlight these specifically
so you don't spend years trying hundreds of different settings
that do practically nothing! I think the real reason Nandub has
so many controls is because it is still in its experimental stage.
The creator of Nandub could no doubt easily make it with only
two or three settings. But instead he gives us full control over
every possible setting and lets us decide what we think works
best. I think this is a great idea and, for this reason alone,
its worth the effort. We are basically beta tester for Nandub.
To prove this certain options (such as half the DRF controls)
have already been ruled out and will probably be removed in future
In this guide I will explain all the controls as I understand
them and I will show you my way of encoding with Nandub. My method
is probably a little different from what most people are doing,
but that doesn't mean I'm doing it a better way! As usual the
more complex the program the less documentation is given so Nandub
comes with a whole single page of no information at all! This
means most of us will not have a clue what any of the controls
really do! I'm not even completely sure how they work myself.
With that word of warning, and if you still feel strong enough
after all that blurb, lets continue.
I'm assuming you are either frameserving from FlasKMpeg
to Nandub following my AVISynth method found Here
or that you are using an AVI file created from the DVD2AVI guide
found Here. Of the two methods I'd say
the DVD2AVI method is the easiest and most reliable so go with
that if you are not sure.
SETTING UP NANDUB
If you haven't already installed VirtualDub 1.4d
I suggest you do so; just put it on a folder on your main drive
(usually C:). Then unzip Nandub and copy all of the contents from
the Nandub folder into the VirtualDub Folder like this:
Thats it! Now to run Nandub you open the VirtualDub
folder and double click on the 'Nandub.exe'
OPENING YOUR AVI / AVS FILE
Since we used DVD2AVI to create an AVI file we can
just open it like we would in VirtualDub. If you are Frameserving
from Flask just open the AVS as normal too.
As I said, Nandub is a hacked versio of VirtualDub
so it also has most of VirtualDub's features. This means that
if you want to crop or resize your movie you can do so in exactly
the same way you would do it in VirtualDub. If you're not sure
how to use VirtualDub for this check out my filter guide Here.
FIRST PASS ENCODING
Normally with MM4 movies such as MakeFilm or AVIRevolution,
FairUse etc., you will need to encode the same movie a few times
so that each one can be joined together. Nandub only ever does
two passes and still gets better results. The first time it encodes
you do not need to set any options in Nandub itself, but you do
need to make sure you have cropped and resized your movie before
this first pass, otherwise you will screw up the process.
Once you used all the crop and resizing filters
you need you will need to make sure it is going to generate a
stats file. Your stats file will contain all the informaton Nandub
find on the 1st pass. So choose:
|Video > SBC Options > Generate
|Video > SBC Options > No AVI
As you can see a tick mark appears by each option
when it is enabled. The 'No AVI output' option is so Nandub doesn't
fill up your hard disk with a movie on this first pass. All we
need it to do is create a stats file on the first pass so we want
No AVI output checked too.
Once that's done we simply go to: File
> First Pass
It will ask you what you want to call your stats
file, so give it any name you like. It will then start encoding.
This will take about as long as encoding the whole movie, so do
it overnight or when you are not using your computer for anything
Once the first pass is done you will end up with
a small binary file called something.stats.
The 1st pass only needs to be done once per movie.
If your movie doesn't turn out very nice after the second pass,
you can still use this stats file again. This saves you needing
to do the 1st pass again and again because it doesn't matter how
you configure the options in Nandub, the stats file always records
the same information from each movie. but obviously you need to
make a new stats file if you are encoding a different movie. You
will also need a new stats file if you change the cropping or
resizing setting etc., so be careful.
SETTING NANDUB OPTIONS
Now that the first pass is over and Nandub has analysed
your movie its time to really encode it. To do this you have to
tell Nandub how you would like it to compress your movie - this
is the complex bit!
First lets set up VirtualDub for keyframe detection.
Go to: Options > Preferences
Click on the Scene tab, move the Interframe cut
to 215 then press save.
Back to the main controls again. Make sure the 'Generate
stats' and 'No AVI output' options are no longer ticked. And we
will go to out first Nandub setting.
Go to: Video > SBC Options
Up pops this dialouge box:
As with all DivX encoding methods the bitrate needs
to be set. Use a bitrate calculator to work out the best setting
to use. I tend to guess the bitrate these days and would probably
put in 1000. You must keep in mind that this is just a rough guide
and it is still possible to go over or under your set filesize
so don't try and be smart and put a huge amount. I'd say always
use the number you calculated from your bitrate calculator! Never
change it even if your movie is far to large or far too small!
The final filesize can be ascertained by altering how the
movie is encoded in other options.
Minimum Allowed Bitrate
This gives Nandub an idea on the minimum quality you want to
keep the movie. I suggest you set it to about 600kbps! Don't bitch
about the best setting for this one because it doesn't seem to
make much difference, just don't go lower than 300kbps and you
should be fine.
The keyframes in Nandub are inserted based on the detection of
scene changes (just like the M4C and VKI codecs that were about
a while ago). If you are not sure what a keyframe is check my
guide Here. In a movie a scene change
is described as when the camera switches from one person to the
next. This produces a huge change in the picture. Since Mpeg compression
is based on only saving the differences between two frames, if
the next frame in the sequence is a completely different one from
the last (as is the case for almost every scene change) then it
is better to start each scene with a whole keyframe rather than
one built out of blocks. And, since all the frames after the first
one of a new scene are based on the first, they will all appear
slightly better quality as a result of the correctly placed keyframe.
In movies the average time between each keyframe is between 2
and 8 seconds.
Nandub's Keyframe interval option is designed to override the
automatic keyframe detection and place keyframes every so many
frames. We don't want this to happen so we set a keyframe only
every 9999 seconds!
Internal Scene Change Detection (SCD) is designed to work in
conjunction with the keyframe detection set in the VirtualDub
preferences. Experimenting with these scene detection options
are pretty futile, nothing you do will make significant improvements
in quality, so there is no need to start pulling out your hair
asking people for the best settings. The settings I have suggested
should keep Nandub form producing too many keyframes. A setting
of 100% for most movies works great on this option, but if you
find it is having problems putting in keyframes on certain movies
(dark movies usually) you can lower it by 10 or 20%.
Space Key Frames (KFs) is in my opinion a very important feature
of the keyframe options. It is possible that the keyframe detection
could become too sensitive at certain parts of the movie and start
inserting loads of keyframes in a row. This could cause jerky
playback or just increase the filesize too much. To prevent this
the Space KF option sets a minimum space of frames between keyframes.
Since the shortest scene in a movie usually lasts at least 2 seconds
we should put 50 frames (which is about two second of time). You
can choose more frames if you think too many keyframes are being
put in your movie or if you really need to save space but its
probably not needed.
Quaint name, eh? Remember when you sometimes got a dead frame
when you were encoding with the old DivX codec and the movie froze
but the audio kept going?! Well this option should help to make
sure that this will never happens again. It is based on the idea
that a corrupt frame has gone off the scale. A setting of 1 reencodes
all frames as a keyframe so we must set it really high to prevent
this happening. I always use 120% on this option and it appears
to work okay. I doubt there is any reason to play around with
other settings unless you notice dead frames or too many keyframes
because of it. This option is turned off by default because it
will slow down encoding. If you've never had problems from frozen
frames then always keep it off it does absolutley nothing except
prevent bad frames.
Go to: Video > SBC Options > Motion
On high motion scenes the DivX codec will increase the bitrate
used and on low motion scenes it will lower the bitrate. This
motion detection is based on noting the differences between frames.
If there are big differences between a sequence of frames this
means there is lots of action. And to store these big differences
we need big amounts of memory. This is why the codec gives more
bitrate on high action scenes and less on low motion scenes. So
this section lets you configure how it detects motion.
Note that the settings above do not seem to work best in all
cases. I've been emailed saying that much better results are gained
by putting the detection up to the full 300. This is especially
the case on very high action movies and some Japanimation movies.
Since the difference in final filesize is only about 300kb more
for a 20 min movie it could well be worth it.
The span is how many frames it compares to determine motion.
The default setting is 8 and that means it will check 8 frames
before the frame its on to 8 frames after the frame its on. So
choosing a setting of 8 detects 16 frames in all (eight to the
left and eight to the right). The smallest amount of frames you
can check would be 1 (one to the left and one to the right). The
highest amount you can check would be 24 frames which is a whole
second to the left and a whole second to the right. Obviously
the more frames you compare the longer it will take to compress.
I see no real reason to choose any other setting than the default
8. You can play around with it but I doubt you will be able to
notice any quality change from another value.
This determines how big a difference between frames it should
check for. The highest most sensitive setting is 1 and the lowest
least sensitive setting is 50 but I doubt it even uses that. The
best setting is probably about 10 but some use as low as 2. The
idea is that if you think the codec is not upping the bitrate
correctly you can make it more or less sensitive to changes. I'm
paranoid so I put 3 like Doom but I doubt it does much better
because of it.
In truth none of these motion detection settings really seem
to make much of a difference. You will not get a significantly
smaller or larger movie by changing them. You will not get a significantly
better quality picture by changing them. There really is no need
to keep asking people what settings are best for these.
Fast Motion & Low Motion
The amount of motion determined in each frame is rated on a scale
from 0 (no action) to 300 (highest action). I have it on good
authority that no matter what movie you have the scale will never
reach the 300% mark. The reason it has a Low Motion and a High
Motion slider bar is to set it so that Fast motion codec can take
over and encode the action parts of the movie while the low motion
codec takes over and encodes the quiet scenes. Since Nandub completely
controls the bitrate there is probably no benefit in doing this
anymore. The fashion with Nandub users is to use only the Low
Motion codec by turning the slider for the Fast Motion up to 300%
so that Nandub can never use it! I actually prefer the opposite!
I turn the Low Motion up to 300% and only use the Fast Motion
codec on the default of 200. Why? Because I have compared the
way Nandub uses the Low Motion codec and the Fast. My conclusion
is that on low motion scenes they look just as good as each other.
But on action scenes the Fast Motion still has a slight edge in
terms of quality and compression. This is to be expected since
the Fast Motion codec was made after the Low Motion codec as an
improvement. Admittedly it didn't seem like an improvement since
they also changed the way it used the bitrate. But Nandub solves
this problem so I see no reason not to use Fast Motion now.
This is similar to the Smoothness / Crispiness setting found
on the original DivX codec. On low action scenes it's better to
keep the movie sharper so it's clearer. But in high action scenes
it's better to make the image slightly blurrier. This blurring
helps to hide macroblocks because it takes less memory to compress
a blurry image than it does to compress a sharp one. The blur
is very subtle and since high action scenes are so fast the human
eye will not notice any loss of detail.
To enable this option you must make sure the Enable BR Modulation
box is ticked. It doesn't really make a big difference what you
set it; the changes are barely noticeable! It basically works
like a backwards version of the DivX Smoothness setting. A 30%
value is equivalent to 70% on the original DivX codec. Most people
use 25-30 but perhaps more is needed for single CD rips or movies
with lots of action.
COMPRESSION LEVELS (ctrl+C)
Go to: Video > SBC Options > Compression
Yes, I know we skipped Bitrate Reservoir but we will get back
to that in a second. This section looks complex but actually it's
the easiest to set of the lot and it will make one of the biggest
differences in final quality.
The DivX codec compresses each frame of a movie based on a compression
ratio of between 0 and 32 percent. The x0 means don't use any
compression and the x32 means use the most compression possible.
In the original Nandub the idea was to let you set the level of
compression exactly for every kind of motion, and that is why
there are six lines to fill in! But soon it became obvious that
this was a waste of time! Instead the only settings you need to
worry about are those on the first line: the DRF min and max setting.
It is very important that you disable all the "when motion
is over" boxes by changing them all to 300; this will literally
turn them off! Hopefully newer releases of Nandub will not have
these extra confusing lines in it.
So what settings should you put in the top Min and Max DRF then?
It appears that the Low Motion codec always used a minimum compression
of x2 and a maximum of x11. Whereas the Fast Motion codec always
used a minimum compression value of x7 and a maximum value of
x16. In truth I believe this to be an oversimplification of the
matter. To illustrate, a statement like that is like saying that
the Fast Motion codec on its best quality setting was not
even as good quality as the Low Motion codec on its worst setting!
So let's talk about practicality instead. Just using 2 as a Min
and 2 as Max settings gives us best possible quality but also
takes far too much space! It is also very, very restrictive and
makes the 2-pass variable bitrate almost a waste of time. You
could quite happily forego the first pass and save yourself a
great deal of time. For Nandub to work efficiently you must give
it a good range of compression. In the case of the original DivX
codec we are assuming ten levels of compression were available
(x2 to x11). For example, what happens when Nandub finds a totally
black screen and all you give it is the ability to compress at
x2? What a waste of space that would be when it could use double
or triple that compression with no quality loss!
In my opinion you should always set the min bitrate
to 2 because you are robbing yourself of the extra quality if
you don't. Higher settings did not go well for me even on single
CD rips. If you are more concerned about making a really, really
small file perhaps using a minimum of 3 or 4 is okay but don't
blame me if it looks crud. After extensive experimentation all
I can say is that a Min of 2 and a Max of 8 give best results
in most cases! I've tried 2-2, 2-3, 2-4 etc., all the way up to
2-16. It appears that the best compression to size ratio for the
average movie is 2-8. Even using 2-4 will not produce a significant
increase in quality and using 2-16 will not produce significantly
more compression. To cut a long story short, I now always use
Min of 2 and a Max of 8! Ironically this is what Doom has said
all along which shows he's been doing his homework :)
BITRATE AND RESERVOIRS (ctrl+B)
Go to: Video > SBC Options > Bitrate
Okay this section is the one that will effect the final quality
of your video the most. It is also the section that is most confusing
to people so I'll take it slow.
Just leave this blank. I think it must be an option inserted
so that the creator of Nandub could test his 1st pass stats creation??
I'm told it is used automatically anyway to create the stats file
anyway, so just ignore it.
On your second pass you will be using the information contained
in the stats file. If you are using someone elses stat file you
can select it by pressing th browse button. Provided you did the
first pass already, this file will already be selected.
Strangely enough this has nothing to do with the amount of compression
that will be used on your video! To illustrate it's use we have
to understand what Nandub actually does with the stats file. On
the first pass your movie is encoded at the best possible quality
a DivX can do (i.e. 6000kbps). As it is compressed instead of
saving the video it examines each frames and detects what bitrate
was used. Since the DivX codec is not looking to fit the movie
in a set space it can go as high or low as is needed for perfect
quality. The stats file in effect is a bitrate graph for that
movie that wuld look a bit like this:
In the stats file the bitrate recorded goes so high that the
low motion scenes could suffer because too much attention is given
to the fast motion scenes. To prevent this the compression setting
can be set to "squash" the bitrate curve down to size.
This in effect takes excess birate from the fast motion scenes
and uses it to improve the low motion scenes. After a compression
of about 20% the graph may look something like this:
As you can see, the bitrate is still variable throughout but
has been compressed so low motion scenes look better and high
motion scenes don't look quite as amazing. Since increasing this
number is essentially flattening out the bitrate curve too much
will totally destroy the stats graph into a flat line. The trick
is to use the minimum amont of compression needed to produce
good low motion scenes. I usually use a setting between 10-30%.
You may have noticed a small calculator button on the right of
this compression setting. This is an automatic feature that tries
to guess the best compression setting based on the information
it has on your video. This is still an experimental feature. If
you go to: Options > Preferences... and click on the tab called
SBC you will see a variable there called the crosspoint. It's
default value is 460 but changing this up and down will vary the
ratio (crosspoint) between its known bitrate graph and the new
value you want. You do not need to use this value at all, you
can just set the compression how you like. The option was created
merely for you to see if you could find automatic settings that
worked every time. Nandubs creator suggests a crosspoint setting
of 460 and some have suggested a value of half that for single
CD rips. As for me I'm not sure, I prefer to go with my gut and
guess the compression value myself.
This helps to stop large jumps in bitrate that may look odd or
just waste space. It is not a blur function and
doesn't soften the image! Imagine it like this; the picture on
the left is the normal stats graph and the picture on the right
is after it has been smoothed:
Leaving it at default setting is fine but I usually set it to
about 2%. Some people seem to go as high as 5% but never use more
than that! Adjusting the smoother isn't going to give significant
increases in quality or compression. If you set it too high, like
ths compression option it will just flatten out the 2-pass encoding
information and make it useless!
Scenes that contain a lot of contrast are difficult to compress.
Mpeg compresses blurry or low contrast images better because there
is less detail in them. If a scene that has a high contrast appears
this option detects it and increases the bitrate to compensate.
The threshold setting represents how high the lumina (or luminance
i.e. brightness difference) needs to be before it will increase
the bitrate for that scene. The Multiplier states by what degree
the bitrate will be increased. The Nandub document suggests setting
a Threshold of 10 and a Multiplier of 5 for most movies. For cartoons
it suggested using Threshold 18 and Multiplier 8 since cartoons
generally have more contrast and sharpness problems. Feel free
to change these as you feel or use the default settings. You can
also just turn the lumina correction off completely it will not
harm your movie to do so. Playing with these settings will probably
not significantly effect the final movie.
This is optional. Before you decide to encode the movie in Nandub
you can go to the end of it and find out how many frames there
are for the end credits. Enter the number here and Nandub will
automatically make sure that they are encoded at half the bitrate
the rest of the movie uses. This can save you about 50MB of space
to its well worth the effort. You do not need to alter any other
settings because Nandub works all the calculations out itself.
The default setting is 0% but you can go upto about 5%. I'm not
sure if it's worth using but I usually keep it 2%. I believe it's
meant to boost the bitrate on the insertion of a keyframe so that
the quality of the frame is slightly higher. I think the idea
is that a better quality first keyframe will result in a better
quality for the whole scene?
Everyone seems to be happy with the default setting of 45 seconds
but it can go upto 120 seconds. The time appears to be specifying
how large a chunk of the movie Nandub is able to share out. If,
for example, there is a lot of action in a movie it may be an
idea to have a higher payback delay so that Nandub can take some
bits from the lower bitrate parts and use them to make action
scenes less blocky. I'm not completely sure how this works but
it doesn't seem to make dramatic changes anyway so have a play
with the setting and see what you think.
High-Pass & Low-Pass
This is almost the same as the Maximum and Minimum bitrate settings
we already choose for the DivX codec. It sounds backwards because
what it calls high is actually the lowest bitrate! What High-Pass
really means is it must encode "higher" than the number
you put in the High-Pass box. So if I put 200 in the High-Pass
box the movie would only encode at a bitrate of 200kbps and higher!
If I put 200kbps in the Low-Pass box it would only encode the
movie at 200kbps and "lower"! Again, you do not need
to be amazingly exact for this one! I usually use 2000kbps in
the Low-Pass box and 600kbps in the High-Pass box, I think these
usually do well for most movies. You can play around with these
settings, as long as you don't put something silly like 1000kbps
in the High-Pass box you shouldn't have any real problems with
I consider the gauge setting the most important setting. Most
of the other settings can be more or less standardised. For example,
you can use DRF of 2-8 on almost all movies. The keyframe and
motion settings can be the same on all movies. The same luma correction
can be used on all movies. The same crispiness modulation can
be used on all movies. The same smoother settings can be used
on all movies. The same payback delay can be used on all movies.
Most movies will even have very similar high and low-pass settings
or compression settings! But once all that is set up you can control
the gauge settings to help control the final size of the movie.
It only takes a little boost one way or the other to increase
or decrease the final filesize.
The gauge actually controls how many bits the DivX codec thinks
are available for encoding each frame. Controlling the gauge is
a bit like setting the bitrate for every frame of the movie. There
are three settings: the Start; the Min and the Max values. Obviously
the Min value is the minimum amount it will allow and the max
is the most it will allow. The starting value is what it will
begin with and it cannot be higher or lower than the other max
or min values. Most people seem to get good results using a Start
and Min of 30-40% and a Max of 80-100%. To increase the size of
the final movie use a smaller Min and Max gauge number. To lower
the size of the movie use a higher min and max gauge number changing
in jumps of 10 or 20. Providing you set up the high and low pass
and that your DivX bitrate settings are correct you shouldn't
end up with a movie that is much smaller or larger than you intended.
Phew! I hope this guide has helped to clarify the controls better.
As I said there is no documentation on this thing so it hard to
know exactly what is going on. So far these settings have been
giving excellent results. Once you have finished setting up Nandub
for the second pass you can finish your movie by choosing: File
> Save As AVI...
And hopefully, after
another nights encoding you will have a movie to be proud of =o)