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

@@ -298,6 +298,13 @@ AudioContext::Stream::getBitRate() const noexcept
     return codecContext->bit_rate;
 }
 
+quint64
+AudioContext::Stream::getLength() const noexcept
+{
+    // The whole file duration, not individual streams.
+    return quint64(std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::microseconds(dataFormat->duration)).count());
+}
+
 // Get the information about the decoded state of this stream
 bool
 AudioContext::Stream::isDecoded() const noexcept