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Subject: Cutting recording (was): Re: Wishful thinking
From: Martin Borus (martin_at_borus.de)
Date: 2002-11-21


rockbox_at_cool.haxx.se schrieb am 21.11.02 12:33:42:
> James Ockwell wrote:
> > Just wondering if we will be able to detect a silence and therefore be able
> > to automatically separate tracks when recording through line in?
>
> Yes, that is certainly possible.
>
> However, the accuracy may be, let's say, non-optimal. :-)
>
> It is a little tricky if we want to split at frame boundaries, but
> otherwise it should be pretty straightforward.

Is this already up for discussion or should we wait until
recording works kind-of flawless? If it is:

In my opinion it is essential to perform the cut on the frame boundaries
so that you can always correct a wrong cut later.

To detect the cut point I'd suggest:
- a minimum time for silence (example 0.5 seconds)
- a max level for silence (example -35 db)
- a minimum time since the last cut (example 120 seconds)

These three selection rules are pretty straightforward.
Another four optional pro features might make it really cool:

- maximum time since last cut (example 900 seconds - cut afterwards)
- max level gain (example 1 db)
- max level gain time (example 60 second)
- remove silence longer then (example 1.9 seconds)

After a cut now there wouldn't be any cuts for 120 seconds at all.
After that, if the sound stayed below -35db for longer then 0.5 seconds,
the frame that has the first audio above -35db would be the first of a new file.

If not cut has been make after 120 + 60 seconds the "max level gain" would hit.
After each "max level gain time" the max level for silence would go up (making a cut
more likely). No matter what happens, after 900 seconds there will be a cut.
The "remove silence longer then" option would be used to make shure unwanted
silence does not get recorded.

Which this set of rules it should be possible to get a right cut point for most
recording situations.

What do you think?

In my opinion this is something for a future version 2.1 rather than 2.0.
I'd love to have it in the end though, because it would be really convenient
to record streaming (satellite/radio) music and CDs this way.

Martin

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