I have googled this but not getting a clear answer.
As far as i understand FLV container format currently support the following audio formats
MP3, ADPCM, Linear PCM, Nellymoser, Speex, AAC, G.711 (reserved for internal use)
Speex is however outdated and has been superseded by Opus which offers all of the functionality of Speex plus additional SILK algorithm implementations etc
So Does Flash support OPUS?
It's not natively supported by the flash player according to adobe: