audio - rendering a waveform on an iphone

Question

I was wondering if anyone has any suggestions on how to go about rendering a waveform of an audio file. I wold like to enable the user to set an in and out point of an audio track and I need to have a waveform so you can see where to put the points.

Are there any libraries available for this or does it need to be a completely custom solution?

Is it even called a waveform ? Maybe there's a better word for it so I can do some more searching.

TIA !

Answer 1

I'm reposting my answer from this question, since it applies here as well:

When displaying an audio waveform, you will want to do some sort of data reduction on the original data, because there is usually more data available in an audio file than pixels on the screen. Most audio editors build a separate file (called a peak file or overview file) which stores a subset of the audio data (usually the peaks and valleys of a waveform) for use at different zoom levels. Then as you zoom in past a certain point you start referencing the raw audio data itself.

Here are some good articles on this:

Waveform Display

As far as source code goes, I would recommend looking through the Audacity source code. Audacity's waveform display is pretty good and mostly likely does a similar sort of data reduction when rendering the waveforms.