The following list gives an overview of parts in ffdshow that are multithreaded and thus show an improvement when run on a multi-core CPU:
libavcodec's MPEG1, MPEG2, and H.264 decoders are multithreaded. The number of cores is automatically detected during ffdshow setup but can be configured under “Decoder options” → “Number of decoding threads”. This setting has no effect on Pentium 4 HT CPUs.
ffmpeg-mt is the multithreaded version of libavcodec and can be used for H.264 decoding.
Xvid, x264, and libavcodec's MPEG1/MPEG2/MPEG4 encoders are multithreaded.
Yadif deinterlacer is multithreaded. No configuration is needed.
The resize filter is fully multithreaded. No configuration is needed.
High quality RGB conversion is multithreaded. No configuration is needed.
With “Queue & misc” → “Queue output samples” checked, acceleration using multithreading is enabled. You may see some benefit even on a single-core CPU.
Rendering of subtitles' glyph is processed by a background thread.