Improve Waveform generation (speed etc.)

[DerGenaue]

This issue exists to track the suggestions made in the comments of #2029;

Especially This comment:

I've dug quite a lot through the the code in the QT app (js, py), libopenshot (C++) and libopenshot-audio to see whether I could also improve the generation of the audio samples in their reduced form.

One thing I wanted to address is the samples_per_second constant, that is stored in two places (py and js).
I would have that constant transmitted together with the data in the JSON.

Also, the waveform data is based on Max-Values (see libopenshot-audio: AuidoSampleBuffer/getMagnitude)
That library also provides RMS values (Mean) which aren't exposed by the libopenshot Frame.
I learned that it is pretty useful to see visually both max peaks and average values, therefore I would propose to also expose this in libopenshot and rewrite the get_waveform python to provide both max and average values
While doing all this, I would also suggest to consistently use waveform_data as a name and not audio_data to make obvious this has a reduced sample rate.

One of the most confusing features imo is that the audio waveform contains the volumes animated on the clip; but only if they exist while the rendering is triggered.

All together, I would suggest to change the waveform JSON data to be changed to something like this:

{
    "sample_rate": 30,
    "maxData": [0.8, 0.5, ...],
    "rmsData": [0.6, 0.2, ...],
}

Which also isn't influenced by the volume values.
They should instead be rendered separately eg. as a red line on top of the waveform.

I wasn't able to implement these changes because of the dependency on the library and because I do not have a development setup right now (literally just edited the files in the installation folder).
Maybe someone of you guys can implement these changes (they should be pretty simple if you have a dev setup)

Other considerations

For speed improvements it also would make a lot of sense in my opinion, to move the generation of the waveform data completely to C++.
It should be integrated with the Clip class and also be cached, I think
I've created another issue for this on the libopenshot-repo:
OpenShot/libopenshot#156

[DerGenaue]

Did this get implemented?
Or what is the reason for closing?

[XanderLeaDaren]

[incomplete feature]
About generation: when changing the volume, there is no immediate change to the waveform height, however when right-click > Display > Show waveform (on an already waveform clip), the wave is updated to the corresponding height.

E.g. you have sound (100%)

1. change it to 30 %.
2. Volume is changed but waveform is not.
3. right-click > Display > Show waveform
4. Waveform is updated to less taller wave.