Enhance waveform rendering

[fengalin]

Displaying the waveforms on a single graph results in a clumsy representation. The first channels rendered are hidden by the last ones if they have larger amplitude.

I don't feel that the channel information is pertinent to the definition of a chapter start or end position. Drawing a mono waveform would reduce the sample buffer, which in turn would reduce the computation needed to draw the waveform and the time spent draining the buffer.

For aesthetic reasons, we could keep the information of which channel has the highest amplitude before mixing down, and draw the sample using a colour matching this channel. It might also be too clumsy though as that could result in a sort of colour patchwork.

[fengalin]

Yes indeed, it doesn't look good with multiple colours. Let's keep it simple.