Calculating File Size from Bitrate

[hgsbnt]

Dear iPoders

I am wondering someday purchasing a new set of earphones. I already have replaced Apple stock earphones by a set of Shure E2c but now I???m considering improving even more my earphones.

Choice shall probably be a pair of Ultimate ears UE-5c http://www.ultimateears.com/UE-5c.htm at US$ 550.00.

When using such high quality earphones, I read ???I would recommend re-encoding your music collection to at least 192Kbps or higher for MP3s or AAC.???

My question is actually the following. Is it somehow possible to calculate how big a file shall be when encoding at 128, 192, 224, 256 kbps ? I???m already encoding in 192 kbps but might consider going to 224 when I???ll be using the UE 5c.

If memory serves me good I found out that same file encoded in 192 kbps require 50% more space when compared to the same file encoded in 128?

Thanks for your help.

[Jesse Hollington]

For Constant Bit Rate files, absolutely...

kbps stands for kilobits per second, which means that for a 128kbps MP3/AAC file, each second of audio requires 128kilobits of data.

Remember as well that we're talking about kiloBITS here, not kilobytes (there are 8 bits in a byte).

So, you can calculate the size using the following formula:

x = length of song (in seconds)
y = bitrate (in kilobits per second)
z = resultant file size (in kilobytes)

(x * y) / 8

We're dividing by 8 above to get the result in bytes.

So if you have a 5 minute song, encoding at 128kbps, you would do this as follows:

5 minutes = 300 seconds
128kbps * 300 seconds = 38,400 kilobits of data
38,400 kilobits / 8 = 4,800 kb

To take this one step further, you can convert this into Megabytes by dividing by 1,024, so 4800/1024 = 4.6875 Mb

The same 5-minute song, encoded at 192kbps would result in:

(192 * 300) / 8 = 7,200 kb (or approx 7Mb).

(Keep in mind also that a kiloBYTE is 1,024 bytes, while a kiloBIT is 1,000 bits.)

This should give you an accurate idea of the filesize to the nearest kilobyte. The exact file size may differ since there other information is usually embedded in the file (tags for song, artist, album, artwork image, etc).

Note that the above formula will not work for variable bit rate files, since (as the name implies) the bit rate is varied throughout the file, so some sections may be 128kbps, and others may be 192kbps, for example.

[jjmpdx]

KBPS is also the classical music station in Portland (89.9fm). But that's probably not what you were asking about...

[n3tfury]

Originally posted by jjmpdx
But that's probably not what you were asking about...

if you would have read his intial post and not just the subject line, you wouldn't have had to waste your time typing.

[shabbs]

Originally posted by hgsbnt
If memory serves me good I found out that same file encoded in 192 kbps require 50% more space when compared to the same file encoded in 128?

That is correct and can be proven mathmatically:

- 128kbps x 1.5 = 192kbps

The 1.5 factor is used to calculate a 50% increase of 128.

jhollington - very nice explanation of file size and kbps. Kudos to you.

Cheers.

[Doug Gilmour]

Originally posted by jhollington
For Constant Bit Rate files, absolutely...

kbps stands for kilobits per second, which means that for a 128kbps MP3/AAC file, each second of audio requires 128kilobits of data.

Remember as well that we're talking about kiloBITS here, not kilobytes (there are 8 bits in a byte).

So, you can calculate the size using the following formula:

x = length of song (in seconds)
y = bitrate (in kilobits per second)
z = resultant file size (in kilobytes)

(x * y) / 8

We're dividing by 8 above to get the result in bytes.

So if you have a 5 minute song, encoding at 128kbps, you would do this as follows:

5 minutes = 300 seconds
128kbps * 300 seconds = 38,400 kilobits of data
38,400 kilobits / 8 = 4,800 kb

To take this one step further, you can convert this into Megabytes by dividing by 1,024, so 4800/1024 = 4.6875 Mb

The same 5-minute song, encoded at 192kbps would result in:

(192 * 300) / 8 = 7,200 kb (or approx 7Mb).

(Keep in mind also that a kiloBYTE is 1,024 bytes, while a kiloBIT is 1,000 bits.)

This should give you an accurate idea of the filesize to the nearest kilobyte. The exact file size may differ since there other information is usually embedded in the file (tags for song, artist, album, artwork image, etc).

Note that the above formula will not work for variable bit rate files, since (as the name implies) the bit rate is varied throughout the file, so some sections may be 128kbps, and others may be 192kbps, for example.

Nice summary there Jesse! Couldn't have said it better myself..

-Dan

[dragfree]

Or you can use these simple approximate guidelines regarding file size per minute of playback time:

WAV, AIFF, .cda 10MB/minute
Lossless 5MB/min
320kbps 2.5MB/min
256 2MB/min
192 1.5MB/min
128 1MB/min

[Kapalua]

So someone help me here...for a newbie who wants superb music quality recording what format and bitrate should I encode in? ACC at 256?

[Doug Gilmour]

Originally posted by Kapalua
So someone help me here...for a newbie who wants superb music quality recording what format and bitrate should I encode in? ACC at 256?

Since your ears are the other things that can tell you what is best for you I'd suggest getting a CD and ripping it into a series of different bit rates. From those you can judge for yourself which are best. Personally I use the EAC/LAME combination at --alt-preset standard (essentially 192 VBR) and have never had a problem.

-Dan

[bdb]

Originally posted by jhollington
Note that the above formula will not work for variable bit rate files, since (as the name implies) the bit rate is varied throughout the file, so some sections may be 128kbps, and others may be 192kbps, for example.

I thought so too, until I started averaging up the MB/min my songs were using. As it turns out, it was just slightly under 1.5MB/min, 50% more than the ~1MB/min that 128kbps CBR uses.

If VBR is based on a specified average bitrate (as I understand it), it shouldn't be too different than CBR. So I think those numbers are good for estimating regardless of CBR or VBR.

Kapalua - you might want to consider using EAC with Lame, with the extreme (or insane) preset. The standard preset produces very good quality, so those should be outstanding. And of course its MP3 so it'll play on just about anything (though if you have a wide variety of players you may want to use CBR, some players can't handle the processing).

[Galley]

The easy way to estimate:
1MB per minute at 128Kbps
1.5MB per minute at 192Kbps

[frantik]

It's really easy just type into google:

XX minutes * YYY kbps

where XX is the song length in minutes and YYY is the bit rate in kbps

google will tell you the answer in megabytes

ex: google.com/search?q=5+minutes+*+192+kbps

you can also do this for videos for you 5G owners

X Minutes * (Y kbps + Z kbps)

where y is video bitrate and z is audio bitrate

[brian10161]

all people have different hearing, plus different music sounds better encoded with different encoders/formats. i listen to soft rock/hard rock and metal, and all of these sound great to me at 128kbps with the AAC encoder. it may seem to be weird and all, but its the honest to gods truth. also, im no audiophile, but i do have good hearing, i just dont really care, 128kbps is fine for me. your best off doing what Doug Gilmour said, get a cd and rip it to different formats/bit rates. you might find that standard AAC encoding at 128kbps is pretty good, but i would try 192VBR if i were you , that might be pretty good. just see what you like , good luck with your encoding.

[moriond]

Use the iPod Storage Calculator posted yesterday to help with your space calculations. For the 5 minute song encoded at 128 kbps from jhollington's example, you can easily see that you'll fit 1017 such songs onto a 5 GB iPod, and 678 songs if you encode at 192 kbps. That's about what you'd guess based on both the estimate (~1 MB/min at 128 kbps -> 5 MB/song) and the calculation (4.6875 MB) -- i.e. a 5 GB capacity is about 1000 times larger -- but the calculator also displays the usable disk space, and adapts its answers to the size of your iPod.

[cappsie]

Hi All

The thing is I need to know how to work out the length as such:

<enclosure url="http://static.podcatch.com/manila/gems/un/TS20041107.mp3" length="49885056" type="audio/mpeg"/>

where the length="49885056" - how exactly can I work that out ?

thanks
Adam