when joining 2x700mb .avi files with ffmpegx the result is 1.37gb

[isaachunt]

When i use ffmpegx to join 2 .avi files of 700mb or more,( with the aim of converting as one to a VIDEO_TS file) the result is always 1.37gb with 30mb or more missing from the end, which means 20, 30 mins or more missing, i could convert the individual .avi's to ffmpegDVD and they will burn to disc, but i can't put them both on one disc to play as one movie, am i missing something?

[j4gg3rr]

1.37G x 1024MB(1G) = 1402.88MB

[isaachunt]

1.37G x 1024MB(1G) = 1402.88MB

ok, now i feel even less computer literate than i did yesterday, but there is still a chunk missing from the end of the movie that is there on the original .avi file, now i'm even more confused, any clues as to why it does this?