Subject: Re: [linux-audio-dev] peakfiles and EDL's
From: Josh Green (jgreen_AT_users.sourceforge.net)
Date: Sun Feb 25 2001 - 00:05:44 EET
Paul Davis wrote:
>
> Design Question Time.
>
> consider the following situation. you are using pre-generated
> peakfiles, containing the max/min amplitudes for every N samples, to
> dislay waveforms. and you're also using an EDL for editing. lets make
> N=2048 for easy thinking.
>
> a user has edited the audio data stream at a point that is 3074
> samples into one file, by inserting another file at that point. you
> now have to recompute the waveform display. You get the first value
> for the first 2048 samples. The next peak value needs to be based on
> the 1024 samples from the first file and the succeeding 1024 samples
> from the next file.
>
> But wait: the peak values are precomputed, and may represent max/min
> values that are not in the sample data that now forms the audio data
> stream (e.g. the min value for the first file's 2nd block of 2048
> might occur at sample 3786). So how can we possibly decide what
> max/min values to use for the 2nd chunk of 2048 samples in the audio
> stream ? Its presumably based on both files, but can we determine it
> without reading the actual audio data for that part of the audio
> stream ?
>
> And it gets worse: what happens if the inserted material is not
> aligned with the first sample of the second file, but is offset. Now,
> every precomputed max/min pair for this file is essentially useless
> because they are "out of phase" with the way the audio is actually
> being used.
>
> Solutions or even suggestions welcome.
>
> --p
Doesn't broadcast 2000 do a lot of this kind of stuff?? Its under the
GPL, not sure what the code looks like though. Lates..
Josh Green
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