encoder: write audio in segments

I'll be honest, this probably makes no noticeable difference at all. It should be faster and more efficient, but whether that translates into any tangible improvement is yet to be seen.

app/codec/ffmpeg/ffmpegencoder.h

@@ -44,8 +44,7 @@ public:
 
   virtual bool WriteFrame(olive::FramePtr frame, olive::rational time) override;
 
-  virtual void WriteAudio(olive::AudioParams pcm_info,
-                          QIODevice *file) override;
+  virtual bool WriteAudio(olive::SampleBufferPtr audio) override;
 
   virtual void Close() override;
 
@@ -74,6 +73,8 @@ private:
   void FlushEncoders();
   void FlushCodecCtx(AVCodecContext* codec_ctx, AVStream *stream);
 
+  bool InitializeResampleContext(SampleBufferPtr audio);
+
   AVFormatContext* fmt_ctx_;
 
   AVStream* video_stream_;
@@ -85,6 +86,9 @@ private:
   AVStream* audio_stream_;
   AVCodecContext* audio_codec_ctx_;
   SwrContext* audio_resample_ctx_;
+  AVFrame* audio_frame_;
+  int audio_frame_offset_;
+  int audio_write_count_;
 
   bool open_;