please allow me to point you to a thread on Hydrogenaudio, discussing a very good idea from mf to convert Foobar2000, a complete-one-library audio player solution into a M$ DirectShow filter with the ability to play some opensource audio formats such as
without the need to make specific DShow filters for them, and also achieving all the other benfits from Foobar2000 like Equalizer, DRC, etc.  ( http://www.hydrogenaudio.org/index.php?act=ST&f=24&t=5866&s=35f3e8a7d761e1eadfb4ac1dd2dc380a ... sorry for the long link, bash Invision board for that ).
The same principle could very well be used to make gstreamer plugins from it, same is valid for BeSweet ( www.doom9.org ), the best audio encoding tool on this world. DSPguru offered many times he would give BeSweet.dll away for other interesting purposes such as a DShow or gstreamer based audio encoder. No idea what it takes to make it compile on Linux though, but if you are interested i will go asking him about it.
BeSweet is offering :
- AC3 input
- AVI input
- MP3 input
- WAV input ( AC3, MP3, PCM, etc. )
- Resampling with SSRC in either 16 Bit, 24 Bit or 32 Bit FP accuracy, including dithering )
- 2 pass normalizing
- 1 pass normalizing ( replaygain, Vorbisgain )
- 5.1 downmix to Stereo, DPL and DPL2 Stereo
- MP2/3 output ( Lame/tolame )
- Vorbis output
- WAV PCM output ( any bitdepth )
etc. ( cant list it all )
and all in one nice DLL :-) . I am convinced it would be quite useful if you got a BeSweet.rm to make a gstreamer plugin from it, please excuse me if i missed the point and was talking rubbish.