ui/prores_aw_handler: Workaround for FFmpeg bug with ProRes in Matroska

In current FFmpeg, whenever Matroska with ProRes is demuxed it creates an atom that is just 8 bytes short of the true size necessary.

We can work around this by padding the actual packet by 8 0x00 bytes, which should result in older FFmpeg versions working fine.

An FFmpeg patch is available: http://ffmpeg.org/pipermail/ffmpeg-devel/2019-September/250724.html

source/ui/prores_aw_handler.hpp

@@ -48,6 +48,8 @@ namespace obsffmpeg {
 
 			virtual void log_options(obs_data_t* settings, const AVCodec* codec,
 			                         AVCodecContext* context) override;
+
+			virtual void process_avpacket(AVPacket& packet, const AVCodec* codec, AVCodecContext* context) override;
 		};
 	} // namespace ui
 } // namespace obsffmpeg