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Topic: How To Detect Mp3pro Bitstream (vs Regular Mp3) ? (Read 5921 times) previous topic - next topic
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How To Detect Mp3pro Bitstream (vs Regular Mp3) ?

What differs in the file to identify a mp3PRO file as opposed to a non-PRO regular mp3? Is it entirely embedded in the audio data, or is there some kind of flag pattern of some sort somewhere I can scan for?

How To Detect Mp3pro Bitstream (vs Regular Mp3) ?

Reply #1 –
Scan for where? You mean on some P2P network? If you're listening to an MP3Pro web-cast such as this one via  Winamp, and if your Winamp is equiped with the MP3Pro plug-in, there'll be an MP3Pro tag after the stream name.

Other than that, "MP3Pro" (the words) would have to be in the external name of the file if you're scanning P2P networks for MP3Pro files.
...:: Kas ::...

How To Detect Mp3pro Bitstream (vs Regular Mp3) ?

Reply #2 –
In the file itself. Does the structure of the MPEG audio frames (or something else) differ in some characteristic way such that I can detect that a mp3 file is actually mp3PRO. Obviously it must differ in some way - mp3PRO-enabled players can tell the difference... So what/where is the difference?

How To Detect Mp3pro Bitstream (vs Regular Mp3) ?

Reply #4 –
It doesn't really identify them. It identifies them as MP3Enc or L3Enc (I forget) MP3's, of which there still are some floating around the net.

How To Detect Mp3pro Bitstream (vs Regular Mp3) ?

Reply #5 –
The one produced by the Thomson demo encoder have an identifiable string.

Otherwise, the criterion would be to look at the ammount of ancillary data. Mp3pro should have more ancillary data (around 4-10kbps)  than regular mp3.

How To Detect Mp3pro Bitstream (vs Regular Mp3) ?

Reply #6 –
What (and where) is the "identifiable string" that the Thompson encoder produces?

But more importantly, please explain what you mean by anciliary data?

How To Detect Mp3pro Bitstream (vs Regular Mp3) ?

Reply #7 –
The major difference in the mp3PRO format is the use of Spectral Band Replication technology.  Unfortunately, most of what I've read about SBR and mp3PRO from Coding Technologies (the developers of SBR) and Thomson Multimedia has been heavy on hype and light on technical detail.  This article in EE Times from a CT marketing  VP actually does the best job of anything I've seen. 


A small example:

"At this point, SBR technology comes into play. SBR uses a hybrid waveform/parametric coding method. It is based on the fact that in most cases there are dependencies between the lower and higher frequency components of an audio signal. Therefore, the high frequency part of an audio signal can be reconstructed from the low frequency part. Transmission of the high frequency part is therefore not necessary. Only a small amount of SBR control data needs to be carried in the bit stream to guarantee an accurate reconstruction of the high frequencies."

While I don't necessarily agree with the leap from "in most cases there are dependencies..." to "Transmission of the high frequency part is therefore not necessary," the description is decent and gets better

The short answer to your questions:

1.  The ancillary data Gabriel refers to is that "small amount of SBR control data needs to be carried in the bit stream to guarantee an accurate reconstruction of the high frequencies."  So, the mp3pro bitstream is split into two pieces:  the mp3 data and the ancillary SBR data.

2.  The easiest way for a layman like me to tell an mp3PRO file is play it in winamp with the mp3pro plugin enabled - the display will say if the file is mp3pro

The next easiest way is to decode the file with an mp3 decoder and then with an mp3pro decoder and compare spectrograms of the two files.  If an mp3pro file is decoded with standard mp3 decoder, you will see that a lowpass filter has cutoff all frequencies above 8-10 kHz (depending on what bitrate you encode) while the mp3pro decoded file will show high frequencies up to 16-22kHz. 

Hope this helps.
Yeah, when you call my name
I salivate like a Pavlov dog...
 

How To Detect Mp3pro Bitstream (vs Regular Mp3) ?

Reply #8 –
Quote
The ancillary data Gabriel refers to is that "small amount of SBR control data needs to be carried in the bit stream to guarantee an accurate reconstruction of the high frequencies." So, the mp3pro bitstream is split into two pieces: the mp3 data and the ancillary SBR data.
But... (the perpetual question) what does this data look like? How does it fit into the audio stream? Is it an integral part of the audio data, or is it stuffed inside some kind of malformed audio frame, à la ID3v2?