Determing File Size Wile in Edit

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Michael G
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Determing File Size Wile in Edit

Post by Michael G » Sun Mar 19, 2017 4:56 pm

Windows 7 Sr1
Audacity 2.1.2

Here is the problem:
When editing any file type for conversion to a MP3 RingTone we must end up with an MP3 file not larger than 200Kb. Can we determine the file size while in the edit mode, before exporting to another MP2 File?

I have already searched the FAQ for ringtones and found how to reduce the original MP3 file, but nowhere is discussed estimating the file size in Kb.

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Re: Determing File Size Wile in Edit

Post by kozikowski » Sun Mar 19, 2017 8:17 pm

I don't know of a good way. File-size predictability is one of the things you give up when you elect for compressed files. I would create several different sound files of predictable length and see how they turn out. We can tell you WAV file sizes down to about ten bytes or so, but that falls apart pretty quickly with MP3, M4A, etc.

Just a note that MP3 files fall apart pretty quickly when you recursively edit them. If you make an MP3 from an MP3, the sound quality is a fraction of either one alone. so if your work starts getting honky and wine-glassy, that's why.


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Re: Determing File Size Wile in Edit

Post by steve » Sun Mar 19, 2017 8:36 pm

If you use "Constant Bit Rate" (CBR) encoding, then the file size is easy to calculate fairly accurately.
For CBR encoding, the "bit rate" is specified in kilobits per second. There are 8 kilobits to a kilobyte. So, for example, if the file is 10 seconds duration and the bit-rate is 128 kbps (kilobits per second), then that is 10 x 128 = 1280 kilobits of data, which = 1280 / 8 = 160 kilobytes.

In short:
Size in kB = bit-rate (kbps) x duration (seconds) / 8

The actual file size will be a little bigger due to headers and metadata, but the above calculation is pretty close.
CBR encoding and the bit-rate (kbps) can be selected in the file export dialog (see: ... ialog.html)
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