Dual Audio Avi Playback question

[Trent]

i have one 1gb avi a 310mb AC3 audio track and anothe 90 mb AC3 track...when i mux them all together using the guide i get an oversized file (30mb+ to each of the 700mb parts)...i tried to take the second track and convert it to MP3 but for some reason i dont lose4 much of the size...i take the 90mb 96kbps AC3 file, convert it to a 50mb 48kbps VBR mp3 file and all i get is 720mb file instead of 730...how come if i reduce the audio file size to 40mb less when i mux them all together i only get 20mb less ?! (could it be the interleaving since the first AC3 track is interleaved every 64ms and the MP3 secondary track every 1 frame)...
i wouldnt like to re-encode the video, overburn the CD (since i want to add subs and more stuff) or even convert the first audio track (wouldnt like to lose the 5 channel AC3)...
does anyone have a solution to this problem ?!

[mustaneekeri]

Could u use Ogg Vorbis for the second track? its has better sound quality at low br's and smaller overhead (smaller file size when muxed)

[theReal]

check out Gknot to see how much overhead double audio tracks produce, vbr mp3 even more than AC3. On a 130 minute movie, overhead for 2xAC3 is 13MB, 1xAC3 & 1x vbr-mp3 is 16MB and 2x vbr-mp3 is 19MB...