MPEG header error

[junior15]

I was wondering if anybody else has seen this error when trying to 
convert mpeg2 video (m2v) to mpeg1 video (m1v) on a Linux PC

**ERROR: Could not read YUV4MPEG header: bad header magic!

Here is the command that I run:
cat alias.m2v | mpeg2dec -o YUVh | mpeg2enc -s -r 24 -o alias.m1v

Also, when trying to use mplex to combine the audio and video files 
(for one MPEG2 file) I get the following error:

[daniel@w... tivo]$ mplex -f 2 -m 2 -o Murder.mpeg2 Murder.m2[av]
INFO: mplex version 2.0.2 ($Date: 2001/09/30 17:13:23 $)
INFO: File Murder.m2a looks like an MPEG Audio stream.
INFO: File Murder.m2v looks like an MPEG-1/2 Video stream.
INFO: Found 1 video streams and 1 audio streams
INFO: Selecting VCD output profile
INFO: Scanning Video stream 0 for access units information.
INFO: VIDEO STREAM: e0
INFO: Frame width : 352
INFO: Frame height : 480
INFO: Aspect ratio : 1:0.6735
INFO: Picture rate : 29.970 frames/sec
INFO: Bit rate : 1470000 bits/sec
INFO: Vbv buffer size : 229376 bytes
INFO: CSPF : 0
INFO: Scanning Audio stream for access units information.
INFO: AUDIO STREAM:
INFO: Audio version : 1.0
INFO: Layer : 3
INFO: CRC checksums : no
INFO: Bit rate : 24576 bytes/sec (192 kbit/sec)
INFO: Frequency : 32000 Hz
INFO: Mode : 0 stereo
INFO: Mode extension : 0
INFO: Copyright bit : 0 no copyright
INFO: Original/Copy : 0 copy
INFO: Emphasis : 0 none
INFO: SYSTEMS/PROGRAM stream:
INFO: rough-guess multiplexed stream data rate : 1701600
INFO: Setting best-guess data rate.
INFO: Sectors = 16 Video delay = 15923 Audio delay = 15923
INFO: New sequence commences...
INFO: Video e0: buf= 47104 frame=000000 sector=00000000
INFO: Audio c0: buf= 4096 frame=000000 sector=00000000
INFO: Padding : sector=00000000
++ WARN: Stream e0: Frame data under-run SCR=288609 DTS=288009 (data 
will arrive
too late to be useful)!
++ WARN: Video e0: buf= 34053 frame=000081 sector=00000216
++ WARN: Audio c0: buf= 2805 frame=000076 sector=00000029
++ WARN: Padding : sector=00000013

{snipped a lot of the same thing}

++ WARN: Stream e0: Frame data under-run SCR=3287160 DTS=3285003 
(data will arri
ve too late to be useful)!
++ WARN: Video e0: buf= 44799 frame=001078 sector=00002878
++ WARN: Audio c0: buf= 2076 frame=001002 sector=00000380
++ WARN: Padding : sector=00000013
**ERROR: Too many frame drops -exiting


Here is the command that I'm running: 
mplex -f 2 -m 2 -o Murder.mpeg2 Murder.m2[av]

If anybody here has seen these errors and can help me figure them 
out, I would appreciate it.

Thanks,
Daniel
junior15@m...