[linux-audio-dev] peakfiles and EDL's

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Subject: [linux-audio-dev] peakfiles and EDL's
From: Paul Davis (pbd_AT_Op.Net)
Date: Sat Feb 24 2001 - 20:46:10 EET


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


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