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Topic: What exactly is freeformat bitstream? (Read 5367 times) previous topic - next topic
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What exactly is freeformat bitstream?

Please pardon my stupid question, but I have seen a lot of reference to freeformat bitstream mp3's, and everybody talks about them like they know exactly what it is, so I feel stupid, but nowhere do I see information on the difference between freeformat bitstream's and regular mp3 bitstreams.  I mean what are the technical differences?  Thanks.

What exactly is freeformat bitstream?

Reply #2 –
Simple version: Free-format simply means that the bitrate is non-standard. Anything from 1 to 640kbps. Most players can't deal with free-format mp3's.

What exactly is freeformat bitstream?

Reply #3 –
Quote
Simple version: Free-format simply means that the bitrate is non-standard.

Something like that
A bit different point of view:
This is extended cbr mode with bitrate that can be any you like and can exceed standart limit of 320Kbit - up to 640Kbit.
May be it helps.

What exactly is freeformat bitstream?

Reply #4 –
So your saying that it basically allows a bitrate of anything I want, instead of the more standard 126, 160, 192, I could choose something like 119, 147 or 212?

Okay, I think I understand now.  I knew it was simple but I couldn't find anything to explain it, so thanks for the link.

What exactly is freeformat bitstream?

Reply #5 –
Quote
So your saying that it basically allows a bitrate of anything I want, instead of the more standard 126, 160, 192, I could choose something like 119, 147 or 212?

Okay, I think I understand now.  I knew it was simple but I couldn't find anything to explain it, so thanks for the link.
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Actually, you can specify a specific bitrate on the encoder command line, like 176 for example. The difference with freeformat is that normal MP3 encoders (and the MP3 standard itself) stops at 320kbps bitrate. Freeformat allows higher non-standard bitrates.

Why anyone would actually want to use those high bitrates is beyond me, there can't be much if any audible benefit and at 640kbps you're basically approaching lossless bitrates, so what's the point? It's still lossy. And it's non-standard and won't play back in most devices or software.

What exactly is freeformat bitstream?

Reply #6 –
Quote
http://mp3decoders.mp3-tech.org/freeformat.html
[a href="index.php?act=findpost&pid=240881"][{POST_SNAPBACK}][/a]


Hello.

I assume those pages ain`t updated.
FreeAmp up to 440 kbps
in_mpg123 up to 560 kbps
l3dec up to 310 kbps
LAME up to 560 kbps
MAD up to 640 kbps
but about useless anyway.

btw. what encoder is CDex.
/edit/

What exactly is freeformat bitstream?

Reply #7 –
Hey, but why WMP is unable to playback freeformat 128kbps stream created with LAME? It seems to me that "freeformat" is something more than just wider bitrate band, am I right?

What exactly is freeformat bitstream?

Reply #8 –
Quote
Hey, but why WMP is unable to playback freeformat 128kbps stream created with LAME? It seems to me that "freeformat" is something more than just wider bitrate band, am I right?
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Why would you do such a thing ? (encoding 128 kbps free-format)
Free-Format with standard bitrates makes no sense. The quality would not be higher or lower this way (compared to 128 kbps CBR non-free-format) but you'll loose playback support.

Free-format is only interesting when you want another non-standard bitrate CBR file above 320 kbps. Below 320 kbps this can also be "simulated" by using something like ABR which results in higher quality (due to VBR mechanism) and higher playback support (due to the usage of standard bitrate frames)

There are four bits in an mp3 frame header which helps decoders to determine the size of the current frame. It's an index to a bitrate table
Code: [Select]
Idx Bitrate (for MPEG1 Layer 3)
--------------
 0   unknown (free-format)
 1   32 kbps
 2   40 kbps
 3   48 kbps
 4   56 kbps
 5   64 kbps
 6   80 kbps
 7   96 kbps
 8  112 kbps
 9  128 kbps
10  160 kbps
11  192 kbps
12  224 kbps
13  256 kbps
14  320 kbps
15  illegal (no valid frame header)

In case of a freeformat bitstream the frame size could be anything (but should be constant for the whole file - exept for the padding stuff) and the decoder has to guess the bitrate according to the distances of the header sync words. This is a bit more complicated to implement and need not to be supported by an mp3 decoder.

Sebastian

What exactly is freeformat bitstream?

Reply #9 –
Quote
need not to be supported by an mp3 decoder.

Just note - Gabriel assure me that freeformat must be supported up to 320Kbit by the iso compliant mp3 decoder...
I can not found his reply on my post, but he states it here http://www.hydrogenaudio.org/forums/index.php?showtopic=1189 too.

What exactly is freeformat bitstream?

Reply #10 –
Quote
Why anyone would actually want to use those high bitrates is beyond me, there can't be much if any audible benefit and at 640kbps you're basically approaching lossless bitrates, so what's the point? It's still lossy. And it's non-standard and won't play back in most devices or software.
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You are right - about mp3 anyway. I tested 384K freeformat and there is still a lowpass filter around 20,000k so psychoacoustics are used, hardly anything can play it. Allof mp3.com might think that its cool for transcoding but it totaly stuffed a sample I tested.

In contrast wavpack (lossy mode) and dualstream quality can be increased progressively until pure lossless is reached - like a bridge between perceptual lossy and lossless. No psymodel only basic quantization noise. Here bitrate inflation *will* fix everything unlike standard perceptual coders. A 384k wavpack will play in foobar , winamp with full seeking, tagging, RG support and it will transcode into anything you throw at it. In theory you can reach real transparency (perceptual + more) at much lower bitrates than lossless. This is probably too 'out of the norm' for most people to bother with but it has a use and I am fascinated by it.

What exactly is freeformat bitstream?

Reply #11 –
Quote
Quote
need not to be supported by an mp3 decoder.

Just note - Gabriel assure me that freeformat must be supported up to 320Kbit by the iso compliant mp3 decoder...
I can not found his reply on my post, but he states it here http://www.hydrogenaudio.org/forums/index.php?showtopic=1189 too.
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I haven't yet checked the specification again but I thought that there's some kind of statement à la "some decoders may not implement freeformat support". In case my memories trick me, I apologize.

Besides... if or if not a compliant decoder has to support freeformat... most available decoders don't (counting also hardware decoders from portables and such).

Sebastian

What exactly is freeformat bitstream?

Reply #12 –
An mp3 decoder MUST support freeformat up to 320kbps, and MAY support it with bitrates higher than 320kbps.

However, in the real world only a few decoders are able to deal with freeformat from 8 to 320kbps.

What exactly is freeformat bitstream?

Reply #13 –
Quote
An mp3 decoder MUST support freeformat up to 320kbps, and MAY support it with bitrates higher than 320kbps.

However, in the real world only a few decoders are able to deal with freeformat from 8 to 320kbps.
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Well, if most decoders don't support it, then it seems just a little bit silly to state that they MUST support it, don't you think? Clearly they don't have to support it because they don't.

What exactly is freeformat bitstream?

Reply #14 –
The ones that don't support it are broken and can't be called "MP3 players". Compare to VBR: An MP3 player will support it. Some things that claim to be don't.