use ffmpeg for sample packing

FFmpeg has a much more optimized algorithm than we do so may as well use it.

app/audio/packedprocessor.h

@@ -0,0 +1,60 @@
+/***
+
+  Olive - Non-Linear Video Editor
+  Copyright (C) 2021 Olive Team
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#ifndef PACKEDPROCESSOR_H
+#define PACKEDPROCESSOR_H
+
+extern "C" {
+#include <libswresample/swresample.h>
+}
+
+#include "codec/samplebuffer.h"
+#include "render/audioparams.h"
+
+namespace olive {
+
+class PackedProcessor
+{
+public:
+  PackedProcessor();
+
+  ~PackedProcessor();
+
+  DISABLE_COPY_MOVE(PackedProcessor)
+
+  bool Open(const AudioParams &params);
+
+  QByteArray Convert(SampleBufferPtr planar);
+
+  void Close();
+
+  bool IsOpen() const
+  {
+    return swr_ctx_;
+  }
+
+private:
+  SwrContext *swr_ctx_;
+
+};
+
+}
+
+#endif // PACKEDPROCESSOR_H