resample `from` and `to` options

[germain-gg]

I have recently started playing around with this library. I have generated a .dat file using the CLI tool with the following command

audiowaveform -i audio.mp3 -o audio.dat -z 256 -b 8

My audio file length is approximately 10 minutes. And I used the resample method to be able to draw a scaled visualisation in an HTML5 Canvas.

Reading through the documentation I noticed two options from and to that can be passed to that method in an options object. However I could not get this to work.

Check the documentation for WaveformData#resample

fetch('audio.mp3')
  .then(response => response.arrayBuffer())
  .then(buffer => {
    const waveform = WaveformData.create(buffer);
    const resampled = waveform.resample({
      width: 500,
      from: 10,
      to: 20
    });
  });

My understanding of those two attributes is that it would return a WaveFormData object from/to a specific time within the audio file (i.e. I want to get my audio sample from second 10 to second 20 and scale them so that they can be drawn on a 500px wide canvas)

After digging in the source code, I could see no reference to from or to in lib/core.js. I'm not sure whether this is still relevant?

I am wondering what would be the right approach using waveform-data.js to achieve what I'd like to do?

I'm happy to PR the documentation updates as needed.

Thank you again for open sourcing this project 💯

[chrisn]

It seems we haven't implemented those options yet. They should work in the same way as the audiowaveform --start, --end, and --width options.

I want to get my audio sample from second 10 to second 20 and scale them so that they can be drawn on a 500px wide canvas

To do this, you'll need to use resample with the scale option and calculate manually:

const timeToPixels = (waveform, time) => 
    Math.floor(time * waveform.adapter.sample_rate / waveform.adapter.scale);

const scale = Math.floor((endTime - startTime) * waveform.adapter.sample_rate / width);
const resampled = waveform.resample({ scale });

const startIndex = timeToPixels(resampled, startTime);
const endIndex = timeToPixels(resampled, endTime);

As the from and to options are not implemented, I'd accept a PR to remove them from the documentation.

We could also look at extending the API to take start, end, and width parameters. Maybe you'd be interested in helping to implement this?

[germain-gg]

Awesome!
Thanks for the code snippet. Let me play around with that

And yeah, I'll have to implement such feature for my app anyway. So I might as well build that in waveform-data.js so that everyone has access to it.

Will PR that early next week 👍