Draft: improve the audio vizualiser

TODO:

• Add time axis
• Add a way to zoom in / zoom out on X axis
• Add a way to change "audio sensibility" for spectrum
• Add the display of timed lines/syl
• Make the timing Bar draggable and reflect the changes in the ASS
• Maybe add lots of rainbowish colors to the spectrum because rainbows are great

src/Lib/Audio.cc

@@ -300,7 +300,7 @@ qreal
 AudioContext::Stream::getLength() const noexcept
 {
     // The whole file duration, not individual streams.
-    return qreal(dataFormat->duration)/1000000;
+    return qreal(std::chrono::duration<qreal,std::ratio<1,1>>(std::chrono::microseconds(dataFormat->duration)).count());
 }
 
 // Get the information about the decoded state of this stream