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[AnonymousTipster]

When using libmad through a sceAudio channel, how do you find data about the current chunk playing? The sort of data that would be needed for a visualizer, ie, current amplitude or tempo of the stream.
I've looked through the FA++1.0 source, but couldn't find anything referencing from an audio stream, except a commented out function pspAudioGetFreq(,) which is apparently deprecated now.

Any help would be much appreciated.

[ufoz]

If you mean equalizer stuff, there are techniques to do that but they are far from trivial. Google for fast fourier transform and beat detection / tempo detection.

Edit: I just realised that might not be what you asked. Looks like you need access to the decoded audio data? You can access that in your 'output' callback that you can specify in mad_decoder_init. At least according to the single source file 'documentation' that libmad provides. :)

[AnonymousTipster]

I'm currently playing the mp3 through a modified version of AhMan's iRShell MP3 player, which doesn't use mad_decoder_init, but I did see this bit of code:

[memon]

You're right, the average of the sample values does not really mean anything (well... it is lowpass filter of some sort). As suggested earlier oneway to do beat detection is to use fourier transform, but there is easier way too :)

Usually it is enough to just use set of band pass filters. That is what I used in my flower demo. Setup the set of bandpass filters at reasonable frequencies (like from 60Hz to 10kHz for example). You can use linear or logarithmic distribution. I think I used logarithmic or something like that :)

I think I used 8 bandpass filters for the flower demo (I dont have the source at hand so I cannot say for sure). I then took tha maximum of two neighbour channels so that in the end I had four values to feed to my effect.

In addition to that I calculated the first derivate of the bandpass values too, which is sometimes more interesting. I also dynamically adjust the min/max of the range, which will really help for the higher frequencies (look the usual output of a winamp and you notice that the there is a noticeable peak at the low freqs).

I can check later if I can find the flower sources. I also used libmad for playback.

[AnonymousTipster]

Thanks for the advice, I'll start looking into band pass filters.

The flower demo does exactly the sort of thing I'm looking to do, if you come across the source code, it would be very beneficial to me, and much appreciated.

[ector]

Actually, you get something very close to an FFT inherently while decoding MP3, which is why WinAMP has always had that visualisation, even back when doing just the decoding took 90% CPU. No time for a separate FFT just for viz...

Of course, not every MP3 playback library will expose this.
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[Shazz]

Obviously we use classic FFT code to go from the time domain to the frequency domain in FA++.

A.T., if you need details, just send me a pm.

Shazz/FA++
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[groepaz]

[memon]

This is how it works :)

[Raphael]

[groepaz]

[Raphael]

Still it's exactly the code, that was asked for in this thread, and is really helpful when you have no experience in audio visualization yet :)

Anyway the full code of the demo would most likely overstrain a lot of people here ;) (Apart from the fact that there only would be thousands of copy-and-paste 'yeah-I-mad'-sum-ubercool-demo' kiddys, so it really is better to keep it closed source)

[groepaz]

[AnonymousTipster]

Just saw the code posted *raises glass to memon*

Thanks a lot. ^_^

[memon]

groepaz, this is getting a bit off topic, but here's the flower thing in a nut shell:

The main stem:
1) pick 2 random numbers, the first is the lenght if a curve and the second is the curvature
2) linearly interpolate along that arc
3) if certain amount of distance has been passed, roll a dice again and based on the random number choose branch or one of petals/flowers
4) loop :)

The branches is handled the same way as the main stem, except that it is only one arc, where the main stem kind of always regenerates itself when it has finished one arc. Each "particle" has a life time whenre it first grows, then lives, and the dies. Depending on the depth of the tree the lifetime is shorter.

The real meat of the effect is how it is synced to the music imho. Basically what I do is that I vary the propability of certain items (especially the branches) based on the music, and also speed of growth (that linear interpolation) is based on the music.

There is also some great philosophical thingking behind the whole thing, but I will not bother with that today ;)

[groepaz]

i see... almost exactly what i thought :)
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