that sux... it seems like mencoder is unable to output aac audio. i saw this on a google search result:

If they're all the same resolution and same framerate, you can use avconv or ffmpeg to output rawvideo, then cat the many outputs to one big file (in sequence) and encode that to a single video. All things being equal of course.

Audio may not be as simple as you might need to fudge a bit. 1601.6 samples per frame at 30 fps (30000/1001) at 48kHz. You'll need to account for full audio for all frames, any failure means audio sync issues.

And any variations in frame rate makes things infinitely more complex to travel that very manual road. KDENLive, lives, cinelerra, and many other more GUI orientated methods to "edit" videos to a product. Probably with a significantly smaller learning curve if you have the hardware to handle it. Since they'll do the math for you most times.

Try:

that is what I did it orginally and it does work but the size of the avi file is almost twice as large as a avi if I could leave the file mv4 it would not be so large