no audio output

[ooohooh]

hello, I'm a VSX4 trial user.
My purpose is to edit some videos from website.
when I split video which has AC3 audio in it , there is no problem (I love VSX4 much)
but when I split video with MP3 audio, its output file has no audio.
I have tested it several times the results are consistent.
to edit videos, I have to convert their audio part to AC3 with virtualdub, it waste my time.
could anyone help me?

here is tested file information

Complete name : D:\down\avi\CD1.avi
Format : AVI
Format/Info : Audio Video Interleave
File size : 700 MiB
Duration : 2h 3mn
Overall bit rate : 794 Kbps
Writing library : VirtualDub build 0/release

Video
ID : 0
Format : MPEG-4 Visual
Codec ID : DIV3
Codec ID/Hint : DivX 3 Low
Duration : 2h 3mn
Bit rate : 653 Kbps
Width : 640 pixels
Height : 240 pixels
Display aspect ratio : 2.667
Frame rate : 23.976 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Compression mode : Lossy
Bits/(Pixel*Frame) : 0.177
Stream size : 576 MiB (82%)

Audio
ID : 1
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 3
Mode : Joint stereo
Mode extension : MS Stereo
Codec ID : 55
Codec ID/Hint : MP3
Duration : 2h 3mn
Bit rate mode : Constant
Bit rate : 128 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Compression mode : Lossy
Stream size : 113 MiB (16%)
Alignment : Aligned on interleaves
Interleave, duration : 24 ms (0.58 video frame)
Interleave, preload duration : 480 ms
Writing library : LAME3.88 (alpha)