LibAudio: Add a sample count hinting mechanism to audio encoding

Userland/Libraries/LibAudio/Encoder.h

@@ -24,6 +24,10 @@ public:
     // This method makes sure that all samples are encoded and written out.
     // This method is called in the destructor, but since this can error, you should call this function yourself before disposing of the decoder.
     virtual ErrorOr<void> finalize() = 0;
+
+    // Provides a hint about the total number of samples to the encoder, improving some encoder's performance in various aspects.
+    // Note that the hint does not have to be fully correct; wrong hints never cause errors, not even indirectly.
+    virtual void sample_count_hint([[maybe_unused]] size_t sample_count) { }
 };
 
 }

Userland/Utilities/aconv.cpp

@@ -141,6 +141,9 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
             return 1;
         }
 
+        if (writer.has_value())
+            (*writer)->sample_count_hint(input_loader->total_samples());
+
         if (output != "-"sv)
             out("Writing: \033[s");