Bitrate Calculator Question...

[RAILheadDesign.com]

Hey all -- newbie here

Looking at the bitrate calc page, I see the formula for manually calculating a bitrate is: (Size - (Audio x Length )) / Length = Video bitrate

I can get the same results (pretty close, at least) when I do the example 90 minutes both manually and via the Java calc -- but when I try to do a video length of 45 minutes at 224 audio, I get results no where close to each other.

The Java Calc gives me 9570, but doing it manually gives me a whopping 13353. That's a difference of 3783 bits! I know the online calc factors-in overhead, but a 3783 higher bitrate is *not* due to overhead.

What am I doing wrong?

TIA,
Maury

[Baldrick]

Nothing wrong. My java bitrate calculator is for dvd and the max dvd bitrate is around 9800Kbits.

[RAILheadDesign.com]

Nothing wrong. My java bitrate calculator is for dvd and the max dvd bitrate is around 9800Kbits.

What I'm asking is why is there such a difference? If the formula on the web page is the same as the formula used in the Java Calc, how can there be such a difference in the results?

The cap is about 9800 so can understand that, but the java calc doesn't yield that high -- it only yields 9570 using my numbers.

Again, I'm not questioning the Java Calc results, I'm just wondering why the manual formula gives such different results.

Do you have the Java Calc source available for viewing anywhere?

TIA,
Maury

[BJ_M]

9570 + the audio bitrate = about 9800

you forgot to include the audio bite rate , the bit rate calc is correct

[RAILheadDesign.com]

9570 + the audio bitrate = about 9800

you forgot to include the audio bite rate , the bit rate calc is correct

So the answer to my question, then, is that the manual formula, which gives the result 13353 (see my first post) is actually correct -- but the Java Calc simply caps it off since 9800 is the max for DVD?

Again, I'm trying to figure out why the math gives different results -- I'm *not* disputing the Java Calc.

Maury

[Baldrick]

Yes, my calculator caps it off.

[RAILheadDesign.com]

Yes, my calculator caps it off.

Thanks for clearing things up for me.

Maury

[RAILheadDesign.com]

I have another Bitrate calculation question: what formula would I use to try and find the max bitrate I could use to match a target final size? For example, if I want my final file size to be 2000MB, what formula can I use to obtain the bitrate that will result in a 2000MB file?

TIA,
Maury

[BJ_M]

use the same formula , just use some algebra and work backwards , though it hurts my head ..

[jimmalenko]

I have another Bitrate calculation question: what formula would I use to try and find the max bitrate I could use to match a target final size? For example, if I want my final file size to be 2000MB, what formula can I use to obtain the bitrate that will result in a 2000MB file?

length * (video + audio) = size

Now we must make an adjustment for the units, so we multiply by 8192 (8 * 1024):

so:
8192 * size in MB/length in seconds= (video + audio) in Kbps

[vhelp]

---> length * (video + audio) = size

Are you saying:

Minutes * (bitrate + audio) = bitrate size ...


If so, then are you saying that:

120 min. * (6000k + 224k) = 720224 bitrate ??

(note, I used to dable w/ bitrate calc's, but its ben a long
times since, and was one of the many things I lost in a
system crash some months ago) Sorry for my *DUMMY'NESS*

-vhelp

[jimmalenko]

---> length * (video + audio) = size

Are you saying:

Minutes * (bitrate + audio) = bitrate size ...

No.

length in seconds
video + audio in Kbps
size will be in Kilobits

now 120 minutes = 7200 seconds

so 7200 * 6224 = size = 44812800

now we must divide by 8192 (8 * 1024) to go from Kilobits (Kb) to MegaBytes (MB).

so 44812800 / 8192 = 5470MB


so we can say that:

(length in seconds * combined bitrate in Kbps)/8192 = size in MB

[vhelp]

Thanks jimmalenko

-vhelp

[johns0]

Another way to figure out the bitrate for 2gb is set to advanced mode in the bitrate calculator and dvd custom size put in 2gb.

[vhelp]

Ok. Wait a second.

I'm confused. In the above that I posted ( and then your
response.. )

What are we getting for our goal here ?
bitrate for encoding ? ...or

Thanks for this thread, I'm throwing together a quick
spreadsheet w/ calculations to give me the answers
(quicly) that I want.

Mine are for my CBR encodes. (not vbr.. or does that
matter)

-vhelp

[jimmalenko]

What are we getting for our goal here ?
bitrate for encoding ? ...or

To find out the final size in MB when we know the rest:
length in seconds * combined bitrate in Kbps)/8192 = size in MB

To find out the combined bitrate we can use to hit a given size:
8192 * size in MB/length in seconds= (video + audio) in Kbps

Mine are for my CBR encodes. (not vbr.. or does that
matter)

The only thing that changes with VBR is that you use this calculated video bitrate as your average. You can set your max and min to whatever you want, but to hit the target size correctly you need to stick to the average that you calculate here.

[RAILheadDesign.com]

Ok. Wait a second.

I'm confused. In the above that I posted ( and then your
response.. )

What are we getting for our goal here ?
bitrate for encoding ? ...or

Thanks for this thread, I'm throwing together a quick
spreadsheet w/ calculations to give me the answers
(quicly) that I want.

-vhelp

Care to share that spreadsheet once you get it made? I'd love to play with it.

TIA,
Maury

[vhelp]

Ok. Wait a second.

I'm confused. In the above that I posted ( and then your
response.. )

What are we getting for our goal here ?
bitrate for encoding ? ...or

Thanks for this thread, I'm throwing together a quick
spreadsheet w/ calculations to give me the answers
(quicly) that I want.

-vhelp

Care to share that spreadsheet once you get it made? I'd love to play with it.

TIA,
Maury

No. Not at this time. However, you can see a tool I'm sculpturing at the
present time. So far, It's working rather well. It's the "re-inventing" the
wheel that sometimes draws too much energy from me, but sometimes,
you just have to.
.. I lost most of my older codes from a prev crash, and that should
.. explain my re-inventing and what-nots)

Anyways. You can jump over here for a demonstration. It's more WYSIWYG
style, because I like to see things move as I go.., not wait for a green light

* Calculating mins from hrs, and other 'math' questions.

-vhelp 3056