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What exactly is Free Format?
geeuhnfay
post May 27 2012, 12:33
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In dBpoweramp when converting files to mp3 it gives the options of vbr, cbr, abr, and also free format. What exactly is free format and how does it compare to the others?
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Porcus
post May 27 2012, 12:47
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QUOTE (geeuhnfay @ May 27 2012, 13:33) *
In dBpoweramp when converting files to mp3 it gives the options of vbr, cbr, abr, and also free format. What exactly is free format and how does it compare to the others?


The «free format» is a less strict specification, allowing for higher bit rates than 320. Which means that an «mp3 player» need not be able to read it. (For all that I know, it might work just fine though.)

It is hardly used anymore (was it ever?), and you are probably better off avoiding it: if you want bigger files than 320, then go lossless (about 900, depending on material).

If you want MP3, go VBR, which adjusts bitrate to complexity. Unless you have an old quirky mp3 player (some of them couldn't handle it, despite labeling themselves as «mp3 players»).


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geeuhnfay
post May 27 2012, 13:01
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Thanks that clears it up, so I'm assuming it's the same as cbr if you set it to 320kbps?

This post has been edited by db1989: May 27 2012, 13:07
Reason for edit: deleting pointless full quote
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[JAZ]
post May 27 2012, 13:05
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"Freeformat" mode of MP3 should not be an option to use inside a program. I guess dbpoweramp offers it thinking mostly with the experienced users.


* The quick reply:
freeformat is a CBR mode which is non-compatible with many players.

* The more complete reply:
The encoded layer 3 data (what is inside an MP3 file) is distributed in packets of fixed size once compressed (huffman encoding). There are only a few fixed sizes for these packets, which in turn determine the only possible CBR values ( i.e. 128, 160, 320..).
Freeformat, instead, does not use packets, but stores the info as a continuous stream.
Doing so offers several advantages:
- Higher than 320kbps bitrates (depending on the decoder/player, up to 640kbps).
- Do codec tweakings not worrying about bit demands. (I guess it was also used in the beginning before standarizing the format)

So in general, it is either a temporary storage (freeformat might not be decodeable with different decoders, so better not rely on it) or an option for developers.
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geeuhnfay
post May 27 2012, 13:22
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Thanks again the compatibility is an issue with iTunes. I just tested it out so I guess I don't have to worry and just leave free format alone.
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benski
post May 27 2012, 18:05
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Decoders are not required to support free format, it is an optional part of the MPEG Audio spec. It is somewhat difficult to support, as the packet size must be "guessed" by looking for the next MPEG header. In practice, few decoders support it.
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