How do I create exact sized MP3's?

[oddball]

I want to be able to create MP3 encodings that fit exact sizes. I use a Mini CD MP3 player and would like to fit 2 or 3 albums on each disc. However if I encode at say 128K bitrate for each album they will either go over or under the limit (Including overburning).

I'd like some method similar to what happens with MPEG4 where you can get it to workout automatically the output size. True the quality may drop or increase depending on the length and complexity the input audio. But for general out and about listening I am not bothered too much.

Thanks.

[Fr4nz]

You can use the --alt-preset xxx command with lame, where xxx is the bitrate you want to achieve (it is named "ABR" which stands for Average-Bit-Rate method).

For more infos: http://www.hydrogenaudio.org/index.php?showtopic=203

[Brother John]

How exact do you need it?
If up to ~5 kbps deviation is ok, then the --alt-preset xxx setting is the way to go as Fr4nz said.
However if you need need a song to be exactly i.e. 4,654,124 bytes CBR mode (--alt-preset cbr xxx) is the only possibility.

[Fr4nz]

Usually ABR achieves exactly the bitrate you wanted, especially if you encode long tracks (like movies ones).

With short tracks (music) it could occur +- ~2kbps deviations which is anyway acceptable.

[pacohaas]

Originally posted by Brother John
How exact do you need it?
If up to ~5 kbps deviation is ok, then the --alt-preset xxx setting is the way to go as Fr4nz said.
However if you need need a song to be exactly i.e. 4,654,124 bytes CBR mode (--alt-preset cbr xxx) is the only possibility. actually, the opposite is true most of the time.

Let's say you need your file to be 143kbps exactly. You can't use CBR here since the closest would be 128 or 160kbps. So you use --alt-preset 143, then wait for the output. If it's slightly too big or small, run the command-line again with an appropriately adjusted bitrate. After 2 or 3 passes, you should have it to exactly the size you wish.

However if you know you want a file that's exactly 128kbps, of course you can just go with --alt-preset cbr 128, but if it were me, I would still go through the trouble of 2 or 3 passes of abr to get a higher quality encode.

edit: oh, and incidently, I have created a small ABR calculator program which you can find in doom9's downloads or on my webpage

[Fr4nz]

Anyway ABR xxx is ALWAYS better than CBR xxx :cool:

[Brother John]

Let's say you need your file to be 143kbps exactly. You can't use CBR here since the closest would be 128 or 160kbps.
Thx for the correction pacohaas. I didn't think about that, but you are right.

[Slogra]

I use Frontah which has an indicator which ABR bitrate you should use.
First you have to set the MB of space you can use at options. Then after you have dropped some wavs (or other formats) it shows the ABR bitrate you should use in the statusbar.

Check it out:
http://home.vxu.se/mdati00/frontah/
btw. It does not work on Win95/98/Me only on Win2000/NT/XP