Without testing, how about something like this...
This is how I pull values from the compression field..
ifelse(isequal([Compression], DTS-HD MA, 8), DTS-HD MA, isequal([Compression], DTS-HD, 8), DTS-HD, isequal([Compression], MP2, 8),MP2, isequal([Compression], pcm_dvd, 8), PCM, isequal([Compression], AAC, 8), AAC, isequal([Compression], DTS-ES, 8), DTS-ES, isequal([Compression], DTS, 8), DTS, isequal([Compression], TRUEHD, 8), Dolby TrueHD, isequal([Compression], AC3, 8), DD, isequal([Compression], Dolby TrueHD, 8), Dolby TrueHD, isequal([Compression],mp3, 8), MP3, isequal([Compression], FLAC, 8), Flac, isequal([Compression], AAC, 8), AAC, isequal([Compression], LPCM, 8), LPCM, isequal([Compression], MPEG-2, 8), MPEG-2, isequal([Compression], WMA 10, 8), WMA 10, 1, NO)