Codec support by Flash version.
Tech Notes
From Wikipedia
Support for audio and video compression formats in Flash Player and in Flash Video[1][9][14][16][18]Flash Player versionReleasedFile formatVideo compression formatsAudio compression formats62002SWFSorenson Spark, Screen videoMP3, ADPCM, Nellymoser72003SWF, FLVSorenson Spark, Screen videoMP3, ADPCM, Nellymoser82005SWF, FLVOn2 VP6, Sorenson Spark, Screen video, Screen video 2MP3, ADPCM, Nellymoser9.0.115.02007SWF, FLVOn2 VP6, Sorenson Spark, Screen video, Screen video 2, H.264[*]MP3, ADPCM, Nellymoser, AAC[*] SWF, F4V, ISO base media file formatH.264AAC, MP3102008SWF, FLVOn2 VP6, Sorenson Spark, Screen video, Screen video 2, H.264[*]MP3, ADPCM, Nellymoser, Speex, AAC[*] SWF, F4V, ISO base media file formatH.264AAC, MP3