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Subject: Re: Re[2]: LOW_WATER and high bitrates
From: Paul Suade (paul.suade_at_laposte.net)
Date: 2002-08-24


back from vacation...

----- Original Message -----
From: "Nielsen Linus (ext)" <Linus.Nielsen_at_elema.siemens.se>
To: <rockbox_at_cool.haxx.se>
Sent: Thursday, August 01, 2002 7:40 AM
Subject: RE: Re[2]: LOW_WATER and high bitrates

> > Are we reading the data from disk and sending it to the mp3
> > decoder without noticing mp3 frames or are we aware of the
> > mp3frames? (I think the first one.)
>
> Definitely the first one.
>
> > How can I find the beginning of an mp3-frame (and find the header)?
>
> You will have to search the bitstream for a frame sync word.
>
> > If that is possible, I think we should update the
> > bitrate-field of the id3tag-struct by making it the
> > average of the ones that were found by
> > now, like:
> >
> > double bitrate_sum = 0.0;
> > double frames_read = 0.0;
> >
> > void DEI3(void) {
> >
> > // reading data from disk
> >
> > // get bitrate of actually read frame
> >
> > bitrate_sum += bitrate_this_frame;
> > frames_read += 1.0;
> > mp3entry.bitrate = (int)(bitrate_sum / frames_read);
> >
> > }
> >
> > (double to prevent overflow)

use 'long long' instead of 'double'.

>
> First of all, it would take the CPU a lot of time to search that data and
> find the frame sync words. Secondly, we don't have floating point support.
> This CPU has no floating point unit. I don't think that is feasible.
>

SH1 has no floating point unit and using an fp emulation library would slow
very much.



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