MPEG2へのエンコードがどうも上手くいきません。
下記のようなメッセージが返されるのですが、どこが悪いのでしょうか？

Welcome to Darwin!
[p230:~] *****% pbpaste | sh
sh: /usr/bin/mpeg2enc: Permission denied
Input #0, mov, from '/Users/*****/Desktop/aaa.mov':
Stream #0.0: Video: dvvideo, 720x480, 29.97 fps
Output #0, yuv4mpegpipe, to 'pipe:':
Stream #0.0: Video: rawvideo, ??, 480x480, 29.97 fps, q=2-31, 200 kb/s
Stream mapping:
Stream #0.0 -> #0.0
Press [q] to stop encoding
YUV4MPEG stream header written. FPS is 30000
Input #0, mov, from '/Users/*****/Desktop/aaa.mov':
Stream #0.0: Video: dvvideo, 720x480, 29.97 fps
No audio or video streams available
INFO: [mplex] mplex version 2.2.1 ($Date: 2002/04/20 19:08:30 $)
**ERROR: [mplex] Unable to open file /Users/*****/Desktop/a.MPG.m2v for reading.
Encoding complete!